On the Photophysics of Polyenes. 1. Bathochromic Shifts in Their 1Ag → 1Bu Electronic Transitions Caused by the Polarizability of the Medium
Identifieur interne : 000E57 ( Istex/Corpus ); précédent : 000E56; suivant : 000E58On the Photophysics of Polyenes. 1. Bathochromic Shifts in Their 1Ag → 1Bu Electronic Transitions Caused by the Polarizability of the Medium
Auteurs : Javier Catala N ; Henning Hopf ; Dagmar Klein ; Meinrad MartusSource :
- The Journal of Physical Chemistry A [ 1089-5639 ] ; 2008.
Abstract
As shown in this study, the solvatochromic behavior of polyenes depends exclusively on the polarizability of the medium and, even more interestingly, their solvatochromism increases markedly with increasing length of the polyene chain. By virtue of the electronic nature of the interaction of polyenes with the medium, their solvatochromic response to a polarizability change is instantaneous, making these compounds extremely effective polarizability probes for molecular environments. The extreme sensitivity of polyenes to the polarizability of their environment is consistent with the fact that changes in molecular architecture such as those occurring in photosynthetic systems can give rise to polarizability gradients resulting in red shifts in the 1Ag → 1Bu transition, thereby opening up new channels directing the energy transfer involved to energy trapping sites in such systems.
Url:
DOI: 10.1021/jp712068f
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<record><TEI wicri:istexFullTextTei="biblStruct"><teiHeader><fileDesc><titleStmt><title>On the Photophysics of Polyenes. 1. Bathochromic Shifts in Their 1Ag → 1Bu Electronic Transitions Caused by the Polarizability of the Medium</title><author><name sortKey="Catala N, Javier" sort="Catala N, Javier" uniqKey="Catala N J" first="Javier" last="Catala N">Javier Catala N</name><affiliation><mods:affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: javier.catalan@uam.es</mods:affiliation></affiliation></author><author><name sortKey="Hopf, Henning" sort="Hopf, Henning" uniqKey="Hopf H" first="Henning" last="Hopf">Henning Hopf</name><affiliation><mods:affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</mods:affiliation></affiliation></author><author><name sortKey="Klein, Dagmar" sort="Klein, Dagmar" uniqKey="Klein D" first="Dagmar" last="Klein">Dagmar Klein</name><affiliation><mods:affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</mods:affiliation></affiliation></author><author><name sortKey="Martus, Meinrad" sort="Martus, Meinrad" uniqKey="Martus M" first="Meinrad" last="Martus">Meinrad Martus</name><affiliation><mods:affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</mods:affiliation></affiliation></author></titleStmt><publicationStmt><idno type="wicri:source">ISTEX</idno><idno type="RBID">ISTEX:FC3122FD255311FC236EDDE88A53120D5A5BC332</idno><date when="2008" year="2008">2008</date><idno type="doi">10.1021/jp712068f</idno><idno type="url">https://api.istex.fr/ark:/67375/TPS-8697FC7D-6/fulltext.pdf</idno><idno type="wicri:Area/Istex/Corpus">000E57</idno><idno type="wicri:explorRef" wicri:stream="Istex" wicri:step="Corpus" wicri:corpus="ISTEX">000E57</idno></publicationStmt><sourceDesc><biblStruct><analytic><title level="a" type="main" xml:lang="en">On the Photophysics of Polyenes. 1. Bathochromic Shifts in Their 1Ag → 1Bu Electronic Transitions Caused by the Polarizability of the Medium</title><author><name sortKey="Catala N, Javier" sort="Catala N, Javier" uniqKey="Catala N J" first="Javier" last="Catala N">Javier Catala N</name><affiliation><mods:affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: javier.catalan@uam.es</mods:affiliation></affiliation></author><author><name sortKey="Hopf, Henning" sort="Hopf, Henning" uniqKey="Hopf H" first="Henning" last="Hopf">Henning Hopf</name><affiliation><mods:affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</mods:affiliation></affiliation></author><author><name sortKey="Klein, Dagmar" sort="Klein, Dagmar" uniqKey="Klein D" first="Dagmar" last="Klein">Dagmar Klein</name><affiliation><mods:affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</mods:affiliation></affiliation></author><author><name sortKey="Martus, Meinrad" sort="Martus, Meinrad" uniqKey="Martus M" first="Meinrad" last="Martus">Meinrad Martus</name><affiliation><mods:affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</mods:affiliation></affiliation></author></analytic><monogr></monogr><series><title level="j" type="main">The Journal of Physical Chemistry A</title><title level="j" type="abbrev">J. Phys. Chem. A</title><idno type="ISSN">1089-5639</idno><idno type="eISSN">1520-5215</idno><imprint><publisher>American Chemical Society</publisher><date type="e-published" when="2008-05-30">2008</date><date when="2008-06-26">2008</date><biblScope unit="vol">112</biblScope><biblScope unit="issue">25</biblScope><biblScope unit="page" from="5653">5653</biblScope><biblScope unit="page" to="5657">5657</biblScope></imprint><idno type="ISSN">1089-5639</idno></series></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">1089-5639</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract">As shown in this study, the solvatochromic behavior of polyenes depends exclusively on the polarizability of the medium and, even more interestingly, their solvatochromism increases markedly with increasing length of the polyene chain. By virtue of the electronic nature of the interaction of polyenes with the medium, their solvatochromic response to a polarizability change is instantaneous, making these compounds extremely effective polarizability probes for molecular environments. The extreme sensitivity of polyenes to the polarizability of their environment is consistent with the fact that changes in molecular architecture such as those occurring in photosynthetic systems can give rise to polarizability gradients resulting in red shifts in the 1Ag → 1Bu transition, thereby opening up new channels directing the energy transfer involved to energy trapping sites in such systems.</div></front></TEI><istex><corpusName>acs</corpusName><keywords><teeft><json:string>polarizability</json:string><json:string>polyenes</json:string><json:string>polyene</json:string><json:string>chem</json:string><json:string>solvatochromic</json:string><json:string>octatetraene</json:string><json:string>ttbpn</json:string><json:string>double bond</json:string><json:string>phys</json:string><json:string>solvatochromism</json:string><json:string>polyene chain</json:string><json:string>solvatochromic behavior</json:string><json:string>electronic transition</json:string><json:string>solvent polarizability</json:string><json:string>chain length</json:string><json:string>ttbp3</json:string><json:string>spectral envelope</json:string><json:string>electronic state</json:string><json:string>different solvent</json:string><json:string>medium increase</json:string><json:string>first electronic transition</json:string><json:string>first absorption band</json:string><json:string>solid line</json:string><json:string>dash line</json:string><json:string>wide range</json:string><json:string>ttbpn compound</json:string><json:string>solvatochromic slope</json:string><json:string>solvent</json:string></teeft></keywords><author><json:item><name>CATALÁN Javier</name><affiliations><json:string>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</json:string><json:string>E-mail: javier.catalan@uam.es</json:string></affiliations></json:item><json:item><name>HOPF Henning</name><affiliations><json:string>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</json:string></affiliations></json:item><json:item><name>KLEIN Dagmar</name><affiliations><json:string>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</json:string></affiliations></json:item><json:item><name>MARTUS Meinrad</name><affiliations><json:string>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</json:string></affiliations></json:item></author><arkIstex>ark:/67375/TPS-8697FC7D-6</arkIstex><language><json:string>unknown</json:string></language><originalGenre><json:string>Article</json:string></originalGenre><abstract>As shown in this study, the solvatochromic behavior of polyenes depends exclusively on the polarizability of the medium and, even more interestingly, their solvatochromism increases markedly with increasing length of the polyene chain. By virtue of the electronic nature of the interaction of polyenes with the medium, their solvatochromic response to a polarizability change is instantaneous, making these compounds extremely effective polarizability probes for molecular environments. The extreme sensitivity of polyenes to the polarizability of their environment is consistent with the fact that changes in molecular architecture such as those occurring in photosynthetic systems can give rise to polarizability gradients resulting in red shifts in the 1Ag → 1Bu transition, thereby opening up new channels directing the energy transfer involved to energy trapping sites in such systems.</abstract><qualityIndicators><score>6.727</score><pdfWordCount>3203</pdfWordCount><pdfCharCount>19982</pdfCharCount><pdfVersion>1.3</pdfVersion><pdfPageCount>5</pdfPageCount><pdfPageSize>589 x 783 pts</pdfPageSize><pdfWordsPerPage>641</pdfWordsPerPage><pdfText>true</pdfText><refBibsNative>true</refBibsNative><abstractWordCount>127</abstractWordCount><abstractCharCount>890</abstractCharCount><keywordCount>0</keywordCount></qualityIndicators><title>On the Photophysics of Polyenes. 1. 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Bathochromic Shifts in Their 1Ag → 1Bu Electronic Transitions Caused by the Polarizability of the Medium</title></titleStmt><publicationStmt><authority>ISTEX</authority><publisher>American Chemical Society</publisher><availability><licence>Copyright © 2008 American Chemical Society</licence><p>American Chemical Society</p></availability><date type="e-published" when="2008-05-30">2008</date><date when="2008-06-26">2008</date><date type="Copyright" when="2008">2008</date></publicationStmt><notesStmt><note type="content-type" source="article" scheme="https://content-type.data.istex.fr/ark:/67375/XTP-6N5SZHKN-D">article</note><note type="publication-type" scheme="https://publication-type.data.istex.fr/ark:/67375/JMC-0GLKJH51-B">journal</note></notesStmt><sourceDesc><biblStruct><analytic><title level="a" type="main" xml:lang="en">On the Photophysics of Polyenes. 1. Bathochromic Shifts in Their 1Ag → 1Bu Electronic Transitions Caused by the Polarizability of the Medium</title><title level="a" type="short">Photophysics of Polyenes</title><author xml:id="author-0000" role="corresp"><persName><surname>Catalán</surname><forename type="first">Javier</forename></persName><affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</affiliation><email>javier.catalan@uam.es</email></author><author xml:id="author-0001"><persName><surname>Hopf</surname><forename type="first">Henning</forename></persName><affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</affiliation></author><author xml:id="author-0002"><persName><surname>Klein</surname><forename type="first">Dagmar</forename></persName><affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</affiliation></author><author xml:id="author-0003"><persName><surname>Martus</surname><forename type="first">Meinrad</forename></persName><affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</affiliation></author><idno type="istex">FC3122FD255311FC236EDDE88A53120D5A5BC332</idno><idno type="ark">ark:/67375/TPS-8697FC7D-6</idno><idno type="DOI">10.1021/jp712068f</idno></analytic><monogr><title level="j" type="main">The Journal of Physical Chemistry A</title><title level="j" type="abbrev">J. Phys. Chem. A</title><idno type="acspubs">jx</idno><idno type="coden">jpcafh</idno><idno type="pISSN">1089-5639</idno><idno type="eISSN">1520-5215</idno><imprint><publisher>American Chemical Society</publisher><date type="e-published" when="2008-05-30">2008</date><date when="2008-06-26">2008</date><biblScope unit="vol">112</biblScope><biblScope unit="issue">25</biblScope><biblScope unit="page" from="5653">5653</biblScope><biblScope unit="page" to="5657">5657</biblScope></imprint></monogr></biblStruct></sourceDesc></fileDesc><profileDesc><abstract><p>As shown in this study, the solvatochromic behavior of polyenes depends exclusively on the polarizability of the medium and, even more interestingly, their solvatochromism increases markedly with increasing length of the polyene chain. By virtue of the electronic nature of the interaction of polyenes with the medium, their solvatochromic response to a polarizability change is instantaneous, making these compounds extremely effective polarizability probes for molecular environments. The extreme sensitivity of polyenes to the polarizability of their environment is consistent with the fact that changes in molecular architecture such as those occurring in photosynthetic systems can give rise to polarizability gradients resulting in red shifts in the 1Ag → 1Bu transition, thereby opening up new channels directing the energy transfer involved to energy trapping sites in such systems.</p></abstract><textClass ana="subject"><keywords scheme="document-type-name"><term>Article</term></keywords><keywords scheme="document-subtype-name"><term>A: Kinetics, Spectroscopy</term></keywords></textClass><langUsage><language ident="zxx"></language></langUsage></profileDesc></teiHeader></istex:fulltextTEI></fulltext><metadata><istex:metadataXml wicri:clean="corpus acs not found" wicri:toSee="no header"><istex:xmlDeclaration>version="1.0" encoding="UTF-8"</istex:xmlDeclaration><istex:document><article specific-use="acs2jats-1.1.23" dtd-version="1.1d1"><front><journal-meta><journal-id journal-id-type="acspubs">jx</journal-id><journal-id journal-id-type="coden">jpcafh</journal-id><journal-title-group><journal-title>The Journal of Physical Chemistry A</journal-title><abbrev-journal-title>J. Phys. Chem. A</abbrev-journal-title></journal-title-group><issn pub-type="ppub">1089-5639</issn><issn pub-type="epub">1520-5215</issn><publisher><publisher-name>American Chemical Society</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.1021/jp712068f</article-id><article-categories><subj-group subj-group-type="document-type-name"><subject>Article</subject></subj-group><subj-group subj-group-type="document-subtype-name"><subject>A: Kinetics, Spectroscopy</subject></subj-group></article-categories><title-group><article-title>On the Photophysics of Polyenes. 1. Bathochromic Shifts in Their 1Ag → 1Bu Electronic Transitions Caused by the Polarizability of the Medium</article-title><alt-title alt-title-type="short">Photophysics of Polyenes</alt-title></title-group><contrib-group><contrib contrib-type="author" corresp="yes" id="ath1"><name name-style="western"><surname>Catalán</surname><given-names>Javier</given-names></name><xref rid="cor1"></xref></contrib><contrib contrib-type="author" id="ath2"><name name-style="western"><surname>Hopf</surname><given-names>Henning</given-names></name></contrib><contrib contrib-type="author" id="ath3"><name name-style="western"><surname>Klein</surname><given-names>Dagmar</given-names></name></contrib><contrib contrib-type="author" id="ath4"><name name-style="western"><surname>Martus</surname><given-names>Meinrad</given-names></name></contrib><aff>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</aff></contrib-group><author-notes><corresp id="cor1"><label>*</label>
Corresponding author. E-mail: <email>javier.catalan@uam.es</email>.</corresp></author-notes><pub-date pub-type="epub"><day>30</day><month>05</month><year>2008</year></pub-date><pub-date pub-type="ppub"><day>26</day><month>06</month><year>2008</year></pub-date><volume>112</volume><issue>25</issue><fpage>5653</fpage><lpage>5657</lpage><history><date date-type="issue-pub"><day>26</day><month>06</month><year>2008</year></date><date date-type="asap"><day>30</day><month>05</month><year>2008</year></date><date date-type="received"><day>25</day><month>12</month><year>2007</year></date><date date-type="rev-recd"><day>19</day><month>02</month><year>2008</year></date></history><permissions><copyright-statement>Copyright © 2008 American Chemical Society</copyright-statement><copyright-year>2008</copyright-year><copyright-holder>American Chemical Society</copyright-holder></permissions><abstract><p>As shown in this study, the solvatochromic behavior of polyenes depends exclusively on the polarizability of the medium and, even more interestingly, their solvatochromism increases markedly with increasing length of the polyene chain. By virtue of the electronic nature of the interaction of polyenes with the medium, their solvatochromic response to a polarizability change is instantaneous, making these compounds extremely effective polarizability probes for molecular environments. The extreme sensitivity of polyenes to the polarizability of their environment is consistent with the fact that changes in molecular architecture such as those occurring in photosynthetic systems can give rise to polarizability gradients resulting in red shifts in the 1Ag → 1Bu transition, thereby opening up new channels directing the energy transfer involved to energy trapping sites in such systems.</p></abstract><custom-meta-group><custom-meta><meta-name>document-id-old-9</meta-name><meta-value>jp712068f</meta-value></custom-meta><custom-meta><meta-name>document-id-new-14</meta-name><meta-value>jp-2007-12068f</meta-value></custom-meta><custom-meta><meta-name>ccc-price</meta-name><meta-value>40.75</meta-value></custom-meta></custom-meta-group></article-meta></front><body><sec id="sec1"><title>Introduction</title><p>Unraveling the photophysical behavior of such biochemically significant structures such as the visual pigments<xref rid="ref1" ref-type="bibr"></xref> and the carotinoid antennae of photophynthesis<named-content content-type="bibref-group"><xref rid="ref2" ref-type="bibr"></xref>,<xref rid="ref3" ref-type="bibr"></xref></named-content> inevitably entails elucidating the photophysics of their polyenic chromophores. The highly dipole-allowed 1Ag → 1Bu transition in such chromophores plays a central role in the detection of visible light and the transfer of the resulting electronic excitation in these systems. As shown long ago by Hausser et al.,<xref rid="ref4" ref-type="bibr"></xref> the most salient photophysical feature of polyenes is their strong first absorption band, the envelope of which exhibits a sharp 0−0 component that can thus be precisely measured. Also, the energy of this absorption band is extremely sensitive to the polarizability of the medium;<named-content content-type="bibref-group"><xref rid="ref5" ref-type="bibr"></xref>–<xref rid="ref6" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ref7" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ref8" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ref9" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ref10" ref-type="bibr"></xref></named-content> even more interesting, however, in relation to the solvatochromic behavior of this electronic transition in polyenes is the fact that both the position and structure of the band are absolutely independent of the polarity and acid−base properties of the medium.<xref rid="ref9" ref-type="bibr"></xref> In summary, the behavior of the 1Ag → 1Bu transition in these compounds has facilitated the establishment of an empirical polarizability scale for molecular environments<xref rid="ref9" ref-type="bibr"></xref> and also the theory of color in organic chemistry.<xref rid="ref11" ref-type="bibr"></xref></p><p>The polarizability features of polyenes have aroused interest among researchers for a long time. Thus, in 1952, Davies<xref rid="ref12" ref-type="bibr"></xref> established a theoretical relationship between the polarizability of an <italic toggle="yes">all</italic>-<italic toggle="yes">trans</italic>-polyene chain containing 1−20 double bonds to the chain length cubed (i.e., he found the polarizability of <italic toggle="yes">all</italic>-<italic toggle="yes">trans</italic> -polyenes to increase more markedly than it would in a simply additive manner with increase in chain length). In 1960, Bramley and Le Fébre<xref rid="ref13" ref-type="bibr"></xref> determined the polarizability of α,ω-diphenylpolyenes with 1−4 double bonds and found it to grow to a greater-than-additive extent. In 2003, one of the authors<xref rid="ref14" ref-type="bibr"></xref> showed in theoretical terms that this polarizability trend is shared by α,ω-diphenylpolyenes with 1−7 double bonds in the chain.</p><p>In 1983, Ponder and Mathies<xref rid="ref15" ref-type="bibr"></xref> examined changes in the absorption spectra for α,ω-diphenylpolyenes with 2−5 double bonds induced by the presence of an electric field and found their polarizability in the ground and first excited electronic states to increase with increasing chain length, the increase growing with the size of the chain to a greater extent in the excited state than in the ground state. The increased polarizability observed in various electronically excited α,ω-diphenylpolyenes (viz. DPB, DPH, DPO and DPD) by Ponder and Mathies<xref rid="ref15" ref-type="bibr"></xref> was confirmed by theoretical computations at the TDDFT level performed by Grozema et al.<xref rid="ref16" ref-type="bibr"></xref> and Ye et al.<xref rid="ref17" ref-type="bibr"></xref></p><p>Because unsubstituted and symmetrically substituted all-<italic toggle="yes">trans</italic>-polyenes are centrosymmetric structures, their electronic states are nonpolar, so any transitions between them will be exclusively influenced by dispersive interactions of the states involved with their environment. As a result, their absorption bands retain their spectral envelope and only change in terms of energy, in a way depending on the balance of the interaction of the polarizability of the electronic states concerned with that of the surrounding molecular environment. Because the polarizability in the 1Bu excited electronic state is higher than that in the ground electronic state, 1Ag, the 1Ag → 1Bu transition will undergo a red shift as the polarizability of the medium increases.</p><p>Therefore, the solvatochromism of a polyene must be proportional to the polarizability difference between the states involved in the electronic transition, which, based on the results of Ponder and Mathies,<xref rid="ref15" ref-type="bibr"></xref> should increase with increasing length of the polyene chain. However, reported results have led to a somewhat confusing situation. Thus, in 1977, Sklar et al.<xref rid="ref6" ref-type="bibr"></xref> studied the solvatochromic behavior of α,ω-diphenylpolyenes with 1, 2, 3, 4, 5, 6 and 8 double bonds in the polyene chain and obtained the following solvatochromic slopes: −6700 ± 300,−9700 ± 500, −10600 ± 500, −10900 ± 500, −9000 ± 900, −9300 ± 700 and −9700 ± 1200 cm<sup>−1</sup>. Thus, the slope increases with the increasing number of double bonds up to four, but then it seems to keep constant for the molecules containing 5, 6 and 8 doubles bonds in the polyene structure. In 1978, Gavin et al.<xref rid="ref5" ref-type="bibr"></xref> studied the solvatochromism of octatetraene in ten different solvents (methanol, pentane, hexane, heptane, isooctane, hexadecane, chloroform, tetrachloromethane, benzene and <italic toggle="yes">o</italic>-dichlorobenzene) and found a good linear relationship between the 0−0 component of the 1Ag → 1Bu transition in octatetraene and the polarizability of the solvent, with a slope of −10 909 ± 1000 cm<sup>−1</sup>. In 1980, D’Amico et al.<xref rid="ref7" ref-type="bibr"></xref> conducted a similar study on decapentaene and decahexaene in five different solvents (methanol, hexane, isooctane, chloroform and benzene) and obtained a slope of −9640 ± 1290 cm<sup>−1</sup> for the former polyene and −9260 ± 1140 cm<sup>−1</sup> for the latter (i.e., the slope seemingly decreased with increasing chain length if compared with the previous result for octatetraene). In 1985, Snyder et al.<xref rid="ref8" ref-type="bibr"></xref> studied tetradecaheptaene in four different solvents (<italic toggle="yes">n</italic>-pentane, <italic toggle="yes">n</italic>-hexane, <italic toggle="yes">n</italic>-hexadecane and benzene) and obtained a slope of −12110 ± 600 cm<sup>−1</sup>, which was thus substantially greater than the previous ones. In summary, available results do not allow one to unambiguously state that the solvatochromism of polyenes increases monotonically with increasing chain length as one would expect.</p><p>In this paper, we revisit the solvatochromism of polyenes by studying ttbPn (3,8-di-<italic toggle="yes">tert</italic>-butyl-2,2,9,9-tetramethyl-3,5,7-decatriene, 3,10-di-<italic toggle="yes">tert</italic>-butyl-2,2,11,11-tetramethyl-3,5,7,9-dodecatetraene, 3,12-di-<italic toggle="yes">tert</italic>-butyl-2,2,13,13-tetramethyl-3,5,7,9,11-tetradecapentaene, 3,14-di-<italic toggle="yes">tert</italic>-butyl-2,2,15,15-tetramethyl-3,5,7,9,11,13-hexadecahexaene, 3,16-di-<italic toggle="yes">tert</italic>-butyl-2,2,17,17-tetramethyl-3,5,7,9,11,13,15-octadecaheptaene, 3,18-di-<italic toggle="yes">tert</italic>-butyl-2,2,19,19-tetramethyl-3,5,7,9,11,13,17-icosaoctaene, 3,20-di-<italic toggle="yes">tert</italic>-butyl-2,2,21,21-tetramethyl-3,5,7,9,11,13,15,17,19-docosanonaene) with <italic toggle="yes">n</italic> = 3−9 double bonds (Scheme <xref rid="sch1"></xref>) to demonstrate that the spectral envelope of the first absorption band for these compounds is insensitive to the natural order of the solvent and that shifts in this band are consistent with changes in the polarizability of the medium. Also, we discuss a potential relationship between solvatochromic shifts in these compounds and the length of their polyene chain.</p><fig id="sch1" position="float" fig-type="scheme" orientation="portrait"><label>1</label><graphic id="gs1" xlink:href="jp-2007-12068f_0003.tif" position="float" orientation="portrait"></graphic></fig></sec><sec id="sec2"><title>Experimental Section</title><p>The polyenes ttbPn with <italic toggle="yes">n</italic> = 3−9 were prepared by McMurry coupling of the corresponding unsaturated aldehydes (uneven number of double bonds) and by Witting olefination of appropriate aldehydes with the respective ylides (even number of double bonds) and chromatographed and recrystallized several times prior to use. On the basis of spectroscopic and chromatographic evidence, the products thus obtained contained no impurities. The synthesis and spectroscopic properties of these compounds, and the preparation of polyenes with up to 13 consecutive double bonds, will be described in a future paper.</p><p>UV−visible spectra were recorded on a Cary-5 spectrophotometer using Suprasil quartz cells of 1 cm light path for dissolved samples at 293 K and 10 cm for gaseous samples at 353 K. Both temperatures were controlled to within ±0.1 °C by means of a Fisons Haake D8 GH thermostat. The solvents used, all in a high purity, were carefully chosen to span a wide range of polarizability (SP)<xref rid="ref9" ref-type="bibr"></xref> and included <italic toggle="yes">n</italic>-hexane (nHex), <italic toggle="yes">n</italic>-heptane (nHep), tetrachloromethane (CCl<sub>4</sub>), chloroform (CHCl<sub>3</sub>), 2-methylbutane (2MB), methanol (MeOH), benzene (ph) and dimethyl sulfoxide (DMSO), all Merck Uvasol-grade, in addition to perfluoro-<italic toggle="yes">n</italic>-hexane (pFnH), 1,2-dichlorobenzene (1,2Clph) and squalane (SQ), all Aldrich and over 99% pure. Squalane was passed through an SiO<sub>2</sub> column prior to use. All solvents were previously checked to contain no substances potentially interfering with the spectra for the ttbPn compounds.</p></sec><sec id="sec3"><title>Results and Discussion</title><p>We shall first confirm that the studied polyenes are only affected by the polarizability of the medium, so they retain the envelope of their first absorption band from solvent to solvent, and then examine the solvatochromic behavior of these polyenes containing 3−9 double bonds to ascertain whether, as expected, it depends on the length of the chain.</p><sec id="sec3.1"><title>Spectral Envelope of the 1Ag → 1Bu Transition in ttbPn</title><p>Figures <xref rid="fig1"></xref><xref rid="fig2" specific-use="suppress-in-print"></xref>–<xref rid="fig3"></xref> show the spectral envelopes for the 1Ag → 1Bu transition of ttbP3 in 2MB, Cl<sub>3</sub>CH and ph; ttbP6 in nHex, CCl<sub>4</sub> and pFHex; and ttbP9 in MeOH, SQ and 1,2Clph; all as normalized with respect to the 0−0 component. As can be seen, the envelope for each polyene changes little with the nature of the solvent. Figure 1 in ref <xref specific-use="ref-style=base-text" rid="ref9" ref-type="bibr"></xref> shows the spectral envelopes for the 1Ag → 1Bu transition of ttbP9 in perfluorohexane, carbon disulfide, hexafluorobenzene, aniline, 2MB, DMSO, acetic acid and tetramethylguanidine. Taking into account that the envelope for ttbP9 is virtually identical in solvents despite the high basicity of tetramethylguanidine, high polarity of DMSO or high acidity of acetic acid, for example, one can conclude that the polyenes respond to perturbations of their polarizability but are completely insensitive to the dipolarity, acidity and basicity of the medium.</p><fig id="fig1" position="float" orientation="portrait"><label>1</label><caption><p>First electronic transition of ttbP3 in chloroform (solid line), benzene (dash line) and 2-methylbutane (dot line), all at 293 K.</p></caption><graphic id="gr3" xlink:href="jp-2007-12068f_0004.tif" position="float" orientation="portrait"></graphic></fig><fig id="fig2" position="float" orientation="portrait"><label>2</label><caption><p>First electronic transition of ttbP6 in terachloromethane (solid line), <italic toggle="yes">n</italic>-hexane (dash line) and <italic toggle="yes">n</italic>-perfluorohexane (dot line), all at 293 K .</p></caption><graphic id="gr4" xlink:href="jp-2007-12068f_0005.tif" position="float" orientation="portrait"></graphic></fig><fig id="fig3" position="float" orientation="portrait"><label>3</label><caption><p>First electronic transition of ttbP9 in 1,2-dichlorobenzene (solid line), squalane (dash line) and methanol (dot line), all at 293 K.</p></caption><graphic id="gr5" xlink:href="jp-2007-12068f_0006.tif" position="float" orientation="portrait"></graphic></fig></sec><sec id="sec3.2"><title>Solvatochromism of ttbPn</title><p>The facts that polarizability is significantly higher in the 1Bu state than in the ground state (1Ag), i.e., that Δα > 0, and that the difference between the two increases with increasing length of the polyene chain,<named-content content-type="bibref-group"><xref rid="ref10" ref-type="bibr"></xref>,<xref rid="ref14" ref-type="bibr"></xref>–<xref rid="ref15" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ref16" ref-type="bibr"></xref></named-content> are quite consistent with the first absorption band for ttbPn compounds undergoing a red shift as the polarizability of the medium increases, but not with the above-described behavior of unsubstituted <italic toggle="yes">all</italic>-<italic toggle="yes">trans</italic>-polyenes<named-content content-type="bibref-group"><xref rid="ref5" ref-type="bibr"></xref>,<xref rid="ref7" ref-type="bibr"></xref>,<xref rid="ref8" ref-type="bibr"></xref></named-content> and α,ω-diphenylpolyenes.<xref rid="ref6" ref-type="bibr"></xref> To our minds, this inconsistency has no easy explanation. For this reason, in this work we examined the solvatochromic behavior of a wide range of <italic toggle="yes">all</italic>-<italic toggle="yes">trans</italic>-ttbPn compounds in 11 solvents spanning an also wide range of polarizability, as formerly done with octatetraene by Gavin et al.<xref rid="ref5" ref-type="bibr"></xref> The solvents used to this end were as follows, arranged according to polarizability: pFHex (SP = 0.3388), 2MB (SP = 0.5813), MeOH (0.6079), <italic toggle="yes">n</italic>-Hex (SP = 0.6164), <italic toggle="yes">n</italic>-Hept (SP = 0.6354), SQ (SP = 0.7139), Cl<sub>4</sub>C (SP = 0.7677), Cl<sub>3</sub>CH (SP= 0.7833), ph (SP = 0.7929), DMSO (SP = 0.8295) and 12Clph (SP = 0.8686). The wavelengths for the 0−0 components of the ttbPn molecules in eleven solvents are gathered in Table <xref rid="tbl1"></xref>.</p><table-wrap id="tbl1" position="float" orientation="portrait"><label>1</label><caption><title>Wavelengths for the 0−0 Component Corresponding to the Transition 1Ag → 1Bu of the ttbPn in Eleven Solvents at 20 C</title></caption><oasis:table><oasis:tgroup cols="8"><oasis:colspec align="left" colname="col1"></oasis:colspec><oasis:colspec align="char" char="." colname="col2"></oasis:colspec><oasis:colspec align="char" char="." colname="col3"></oasis:colspec><oasis:colspec align="char" char="." colname="col4"></oasis:colspec><oasis:colspec align="char" char="." colname="col5"></oasis:colspec><oasis:colspec align="char" char="." colname="col6"></oasis:colspec><oasis:colspec align="char" char="." colname="col7"></oasis:colspec><oasis:colspec align="char" char="." colname="col8"></oasis:colspec><oasis:thead><oasis:row><oasis:entry align="center">solvent</oasis:entry><oasis:entry align="center">ttbP3</oasis:entry><oasis:entry align="center">ttbP4</oasis:entry><oasis:entry align="center">ttbP5</oasis:entry><oasis:entry align="center">ttbP6</oasis:entry><oasis:entry align="center">ttbP7</oasis:entry><oasis:entry align="center">ttbP8</oasis:entry><oasis:entry align="center">ttbP9</oasis:entry></oasis:row></oasis:thead><oasis:tbody><oasis:row><oasis:entry>pFHex</oasis:entry><oasis:entry>301.0</oasis:entry><oasis:entry>332.4</oasis:entry><oasis:entry>359.6</oasis:entry><oasis:entry>383.4</oasis:entry><oasis:entry>404.9</oasis:entry><oasis:entry>422.1</oasis:entry><oasis:entry>439.3</oasis:entry></oasis:row><oasis:row><oasis:entry>2MB</oasis:entry><oasis:entry>306.0</oasis:entry><oasis:entry>339.2</oasis:entry><oasis:entry>367.4</oasis:entry><oasis:entry>394.3</oasis:entry><oasis:entry>417.0</oasis:entry><oasis:entry>436.4</oasis:entry><oasis:entry>456.1</oasis:entry></oasis:row><oasis:row><oasis:entry>MeOH</oasis:entry><oasis:entry>306.0</oasis:entry><oasis:entry>339.7</oasis:entry><oasis:entry>369.2</oasis:entry><oasis:entry>395.6</oasis:entry><oasis:entry>418.8</oasis:entry><oasis:entry>437.5</oasis:entry><oasis:entry>458.1</oasis:entry></oasis:row><oasis:row><oasis:entry>n-Hex</oasis:entry><oasis:entry>306.3</oasis:entry><oasis:entry>340.0</oasis:entry><oasis:entry>369.4</oasis:entry><oasis:entry>395.6</oasis:entry><oasis:entry>419.4</oasis:entry><oasis:entry>437.9</oasis:entry><oasis:entry>458.8</oasis:entry></oasis:row><oasis:row><oasis:entry>n-Hept</oasis:entry><oasis:entry>306.7</oasis:entry><oasis:entry>340.5</oasis:entry><oasis:entry>370.1</oasis:entry><oasis:entry>396.6</oasis:entry><oasis:entry>419.9</oasis:entry><oasis:entry>439.1</oasis:entry><oasis:entry>460.1</oasis:entry></oasis:row><oasis:row><oasis:entry>SQ</oasis:entry><oasis:entry>308.1</oasis:entry><oasis:entry>342.4</oasis:entry><oasis:entry>373.1</oasis:entry><oasis:entry>399.9</oasis:entry><oasis:entry>424.8</oasis:entry><oasis:entry>444.8</oasis:entry><oasis:entry>466.1</oasis:entry></oasis:row><oasis:row><oasis:entry>Cl<sub>4</sub>C</oasis:entry><oasis:entry>310.6</oasis:entry><oasis:entry>345.2</oasis:entry><oasis:entry>376.4</oasis:entry><oasis:entry>403.9</oasis:entry><oasis:entry>428.2</oasis:entry><oasis:entry>448.4</oasis:entry><oasis:entry>470.2</oasis:entry></oasis:row><oasis:row><oasis:entry>Cl<sub>3</sub>CH</oasis:entry><oasis:entry>310.2</oasis:entry><oasis:entry>345.9</oasis:entry><oasis:entry>376.5</oasis:entry><oasis:entry>403.9</oasis:entry><oasis:entry>429.3</oasis:entry><oasis:entry>449.7</oasis:entry><oasis:entry>471.4</oasis:entry></oasis:row><oasis:row><oasis:entry>Ph</oasis:entry><oasis:entry>310.9</oasis:entry><oasis:entry>345.5</oasis:entry><oasis:entry>376.8</oasis:entry><oasis:entry>404.6</oasis:entry><oasis:entry>429.5</oasis:entry><oasis:entry>449.8</oasis:entry><oasis:entry>472.2</oasis:entry></oasis:row><oasis:row><oasis:entry>DMSO</oasis:entry><oasis:entry>311.6</oasis:entry><oasis:entry>346.3</oasis:entry><oasis:entry>377.2</oasis:entry><oasis:entry>406.0</oasis:entry><oasis:entry>431.2</oasis:entry><oasis:entry>452.0</oasis:entry><oasis:entry>475.9</oasis:entry></oasis:row><oasis:row><oasis:entry>12Clph</oasis:entry><oasis:entry>312.5</oasis:entry><oasis:entry>348.0</oasis:entry><oasis:entry>379.7</oasis:entry><oasis:entry>408.7</oasis:entry><oasis:entry>434.2</oasis:entry><oasis:entry>455.2</oasis:entry><oasis:entry>478.3</oasis:entry></oasis:row></oasis:tbody></oasis:tgroup></oasis:table></table-wrap><p>Figure <xref rid="fig4"></xref> illustrates the solvatochromic behavior of the studied compounds by a plot of the frequency of the 0−0 component for the 1Ag → 1Bu transition against the solvent polarizability expressed in terms of SP.<xref rid="ref9" ref-type="bibr"></xref> As expected, lengthening the polyene chain (i.e., expanding the molecular box) decreases the energy of the transition; as a result, the distance between the curves describing the solvatochromism of consecutive polyenes decreases with increasing chain length.</p><fig id="fig4" position="float" orientation="portrait"><label>4</label><caption><p>Solvatochromic behavior of ttbPn with <italic toggle="yes">n</italic> = 3−9 as established by plotting the 0−0 component for their 1Ag → 1Bu transition against the empirical polarizability<xref rid="ref9" ref-type="bibr"></xref> of the following solvents: pFHex (SP = 0.3388), 2MB (SP = 0.5813), MeOH (SP = 0.6079), <italic toggle="yes">n</italic>-Hex (SP = 0.6164), <italic toggle="yes">n</italic>-Hept (SP = 0.6354), SQ (SP = 0.7139), Cl<sub>4</sub>C (SP = 0.7677), Cl<sub>3</sub>CH (SP = 0.7833), ph (SP = 0.7929), DMSO (SP = 0.8295) and 12Clph (SP = 0.8686).</p></caption><graphic id="gr6" xlink:href="jp-2007-12068f_0007.tif" position="float" orientation="portrait"></graphic></fig><p>As can be seen from Table <xref rid="tbl2"></xref>, all curves were fitted with coefficients better than 0.99 and small standard deviations, less than 45 cm<sup>−1</sup>. It should be noted that the zero polarizability value in each fitted curve would correspond to the 0−0 component of the transition as measured in the absence of solvent (i.e., in the gas phase). Interestingly, the solvatochromically calculated 0−0 component for ttbP3 was 34 072 ± 66 cm<sup>−1</sup>, which is quite consistent with the measured value in the gas phase at 353 K (see Figure <xref rid="fig5"></xref>): 34100 cm<sup>−1</sup>. The corresponding value for ttbP4, 30976 ± 51 cm<sup>−1</sup>, is also consistent with that in the gas phase at 353 K: 31104 cm<sup>−1</sup>.<xref rid="ref18" ref-type="bibr"></xref></p><table-wrap id="tbl2" position="float" orientation="portrait"><label>2</label><caption><title>Statistical Correlations for the <italic toggle="yes">v</italic><sup>0−0</sup> of the Electronic Transition 1Ag → 1Bu vs the Empirical Solvent Polarizability (SP)[9] or vs the Polarizability Equation (<italic toggle="yes">n</italic><sup>2</sup> − 1)/(<italic toggle="yes">n</italic><sup>2</sup> + 2)(α) for the Eleven Solvents Employed</title></caption><oasis:table><oasis:tgroup cols="6"><oasis:colspec align="left" colname="col1"></oasis:colspec><oasis:colspec align="left" colname="col2"></oasis:colspec><oasis:colspec align="char" char=" " colname="col3"></oasis:colspec><oasis:colspec align="char" char=" " colname="col4"></oasis:colspec><oasis:colspec align="char" char="." colname="col5"></oasis:colspec><oasis:colspec align="char" char="." colname="col6"></oasis:colspec><oasis:thead><oasis:row><oasis:entry align="center" valign="bottom">compound</oasis:entry><oasis:entry align="center" valign="bottom">polarizability</oasis:entry><oasis:entry align="center" valign="bottom">slope (cm<sup>−1</sup>)</oasis:entry><oasis:entry align="center" valign="bottom">intercept(cm<sup>−1</sup>)</oasis:entry><oasis:entry align="center" valign="bottom"><italic toggle="yes">r</italic></oasis:entry><oasis:entry align="center" valign="bottom">sd(cm<sup>−1</sup>)</oasis:entry></oasis:row></oasis:thead><oasis:tbody><oasis:row><oasis:entry>ttbP3</oasis:entry><oasis:entry>SP</oasis:entry><oasis:entry>−2364 ± 94</oasis:entry><oasis:entry>34072 ± 66</oasis:entry><oasis:entry>0.993</oasis:entry><oasis:entry>45</oasis:entry></oasis:row><oasis:row><oasis:entry></oasis:entry><oasis:entry>α</oasis:entry><oasis:entry>−7553 ± 654</oasis:entry><oasis:entry>34341 ± 166</oasis:entry><oasis:entry>0.968</oasis:entry><oasis:entry>95</oasis:entry></oasis:row><oasis:row><oasis:entry>ttbP4</oasis:entry><oasis:entry>SP</oasis:entry><oasis:entry>−2564 ± 73</oasis:entry><oasis:entry>30976 ± 51</oasis:entry><oasis:entry>0.996</oasis:entry><oasis:entry>35</oasis:entry></oasis:row><oasis:row><oasis:entry></oasis:entry><oasis:entry>α</oasis:entry><oasis:entry>−8106 ± 781</oasis:entry><oasis:entry>31245 ± 190</oasis:entry><oasis:entry>0.961</oasis:entry><oasis:entry>113</oasis:entry></oasis:row><oasis:row><oasis:entry>ttbP5</oasis:entry><oasis:entry>SP</oasis:entry><oasis:entry>−2822 ± 55</oasis:entry><oasis:entry>28787 ± 39</oasis:entry><oasis:entry>0.998</oasis:entry><oasis:entry>26</oasis:entry></oasis:row><oasis:row><oasis:entry></oasis:entry><oasis:entry>α</oasis:entry><oasis:entry>−8902 ± 914</oasis:entry><oasis:entry>29071 ± 231</oasis:entry><oasis:entry>0.956</oasis:entry><oasis:entry>132</oasis:entry></oasis:row><oasis:row><oasis:entry>ttbP6</oasis:entry><oasis:entry>SP</oasis:entry><oasis:entry>−3023 ± 53</oasis:entry><oasis:entry>27122 ± 37</oasis:entry><oasis:entry>0.999</oasis:entry><oasis:entry>25</oasis:entry></oasis:row><oasis:row><oasis:entry></oasis:entry><oasis:entry>α</oasis:entry><oasis:entry>−9595 ± 844</oasis:entry><oasis:entry>27449 ± 214</oasis:entry><oasis:entry>0.967</oasis:entry><oasis:entry>123</oasis:entry></oasis:row><oasis:row><oasis:entry>ttbP7</oasis:entry><oasis:entry>SP</oasis:entry><oasis:entry>−3155 ± 41</oasis:entry><oasis:entry>25790 ± 28</oasis:entry><oasis:entry>0.999</oasis:entry><oasis:entry>20</oasis:entry></oasis:row><oasis:row><oasis:entry></oasis:entry><oasis:entry>α</oasis:entry><oasis:entry>−9963 ± 1000</oasis:entry><oasis:entry>26110 ± 253</oasis:entry><oasis:entry>0.957</oasis:entry><oasis:entry>145</oasis:entry></oasis:row><oasis:row><oasis:entry>ttbP8</oasis:entry><oasis:entry>SP</oasis:entry><oasis:entry>−3279 ± 44</oasis:entry><oasis:entry>24824 ± 31</oasis:entry><oasis:entry>0.999</oasis:entry><oasis:entry>21</oasis:entry></oasis:row><oasis:row><oasis:entry></oasis:entry><oasis:entry>α</oasis:entry><oasis:entry>−10395 ± 884</oasis:entry><oasis:entry>25182 ± 224</oasis:entry><oasis:entry>0.969</oasis:entry><oasis:entry>129</oasis:entry></oasis:row><oasis:row><oasis:entry>ttbP9</oasis:entry><oasis:entry>SP</oasis:entry><oasis:entry>−3527 ± 25</oasis:entry><oasis:entry>23968 ± 17</oasis:entry><oasis:entry>0.999</oasis:entry><oasis:entry>12</oasis:entry></oasis:row><oasis:row><oasis:entry></oasis:entry><oasis:entry>α</oasis:entry><oasis:entry>−11110 ± 1006</oasis:entry><oasis:entry>24344 ± 255</oasis:entry><oasis:entry>0.965</oasis:entry><oasis:entry>146</oasis:entry></oasis:row></oasis:tbody></oasis:tgroup></oasis:table></table-wrap><fig id="fig5" position="float" orientation="portrait"><label>5</label><caption><p>1Ag → 1Bu electronic transition for ttbP3 in the gas phase at 353 K.</p></caption><graphic id="gr7" xlink:href="jp-2007-12068f_0008.tif" position="float" orientation="portrait"></graphic></fig><p>The consistency of the solvatochromically predicted 0−0 components for the 1Ag ± 1Bu electronic transition with available measured data in the gas phase (see Table <xref rid="tbl2"></xref>) allows one to adopt these solvatochromic predictions for longer ttbPn compounds, where obtaining a measurable sample by raising the temperature in the gas phase is impossible. Determining the corresponding 0−0 components enables a deeper analysis of these compounds in light of the one-dimensional box model. As shown by available XRD data,<xref rid="ref19" ref-type="bibr"></xref> <italic toggle="yes">all</italic>-<italic toggle="yes">trans</italic>-ttbP compounds are elongated molecules resembling a one-dimensional box; this can facilitate rationalization of their spectral behavior in terms of this quantum model. The treatment involved implicitly considers all π electrons in the compound and assumes the box length to coincide with the distance between the terminal carbon in the polyene chain and be <italic toggle="yes">L</italic> = <italic toggle="yes">r</italic>(<italic toggle="yes">C</italic><sub>1</sub> − <italic toggle="yes">C′</italic><sub>1</sub>) as inferred from X-ray data.<xref rid="ref19" ref-type="bibr"></xref></p><p>The energy levels available within a one-dimensional box can be quantified as
<disp-formula id="eq1"><label>1</label><alternatives><graphic xlink:href="jp-2007-12068f_m001.gif" orientation="portrait" position="float"></graphic><mml:math display="block" overflow="scroll"><mml:mrow><mml:mi>E</mml:mi><mml:mo>=</mml:mo><mml:msup><mml:mrow><mml:mtext mathvariant="italic">h</mml:mtext></mml:mrow><mml:mrow><mml:mtext>2</mml:mtext></mml:mrow></mml:msup><mml:msup><mml:mrow><mml:mi>n</mml:mi></mml:mrow><mml:mrow><mml:mtext>2</mml:mtext></mml:mrow></mml:msup><mml:mtext>/8</mml:mtext><mml:mtext mathvariant="italic">m</mml:mtext><mml:msup><mml:mrow><mml:mi>L</mml:mi></mml:mrow><mml:mrow><mml:mtext>2</mml:mtext></mml:mrow></mml:msup></mml:mrow></mml:math></alternatives></disp-formula>
where <italic toggle="yes">h</italic> is the Planck constant, <italic toggle="yes">m</italic> is the mass of the particle held in the box, <italic toggle="yes">L</italic> is the box length and <bold><italic toggle="yes">n</italic></bold> is an integer (1, 2, 3, ...).</p><p>The first electronic transition of interest to this study on ttbPn is 1Ag → 1Bu, known to involve an electronic transition between the HOMO and LUMO (i.e., between levels <italic toggle="yes">n</italic> and <italic toggle="yes">n</italic> + 1 in the box, <italic toggle="yes">n</italic> coinciding with the number of double bonds in the compound). Let us evaluate the energy of this <italic toggle="yes">n</italic> → <italic toggle="yes">n</italic> + 1 transition from the energy levels available for a particle in a box:</p><p><disp-formula id="eq2"><label>2</label><alternatives><graphic xlink:href="jp-2007-12068f_m002.gif" orientation="portrait" position="float"></graphic><mml:math display="block" overflow="scroll"><mml:mrow><mml:mi mathvariant="normal">Δ</mml:mi><mml:msub><mml:mrow><mml:mi>E</mml:mi></mml:mrow><mml:mrow><mml:mtext>(</mml:mtext><mml:mtext mathvariant="italic">n</mml:mtext><mml:mo>→</mml:mo><mml:mtext></mml:mtext><mml:mtext mathvariant="italic">n</mml:mtext><mml:mtext>+1)</mml:mtext></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:msup><mml:mrow><mml:mtext mathvariant="italic">h</mml:mtext></mml:mrow><mml:mrow><mml:mtext>2</mml:mtext></mml:mrow></mml:msup><mml:mtext>/8</mml:mtext><mml:mi>m</mml:mi><mml:mo>)</mml:mo></mml:mrow><mml:mo stretchy="false">(</mml:mo><mml:mtext>2</mml:mtext><mml:mi>n</mml:mi><mml:mo>+</mml:mo><mml:mtext>1</mml:mtext><mml:mo stretchy="false">)</mml:mo><mml:mtext>/</mml:mtext><mml:msup><mml:mrow><mml:mi>L</mml:mi></mml:mrow><mml:mrow><mml:mtext>2</mml:mtext></mml:mrow></mml:msup></mml:mrow></mml:math></alternatives></disp-formula>
which can be rewritten as</p><p><disp-formula id="eq3"><label>3</label><alternatives><graphic xlink:href="jp-2007-12068f_m003.gif" orientation="portrait" position="float"></graphic><mml:math display="block" overflow="scroll"><mml:mrow><mml:msub><mml:mrow><mml:mtext>λ</mml:mtext></mml:mrow><mml:mrow><mml:mtext>(</mml:mtext><mml:mtext mathvariant="italic">n</mml:mtext><mml:mo>→</mml:mo><mml:mtext mathvariant="italic">n</mml:mtext><mml:mtext>+1)</mml:mtext></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mo stretchy="false">(</mml:mo><mml:mtext>8</mml:mtext><mml:mi>c</mml:mi><mml:mi>m</mml:mi><mml:mtext>/</mml:mtext><mml:mtext mathvariant="italic">h</mml:mtext><mml:mo stretchy="false">)</mml:mo><mml:mrow><mml:mo>[</mml:mo><mml:msup><mml:mrow><mml:mi>L</mml:mi></mml:mrow><mml:mrow><mml:mtext>2</mml:mtext></mml:mrow></mml:msup><mml:mtext>/</mml:mtext><mml:mo stretchy="false">(</mml:mo><mml:mtext>2</mml:mtext><mml:mi>n</mml:mi><mml:mo>+</mml:mo><mml:mtext>1</mml:mtext><mml:mo stretchy="false">)</mml:mo><mml:mo>]</mml:mo></mml:mrow></mml:mrow></mml:math></alternatives></disp-formula>
Based on eq <xref rid="eq3"></xref>, the wavelength of the electronic transition must change linearly with <italic toggle="yes">L</italic><sup>2</sup>/(2<italic toggle="yes">n</italic> + 1) in these compounds. Figure <xref rid="fig6"></xref> illustrates the excellent correlation between the transition wavelength as evaluated solvatochromically (see Table <xref rid="tbl2"></xref>) and the term <italic toggle="yes">L</italic><sup>2</sup>/(2<italic toggle="yes">n</italic> + 1) in all studied compounds.</p><fig id="fig6" position="float" orientation="portrait"><label>6</label><caption><p>Variation of the wavelength of the 0−0 component for the ttbP compounds studied with the term <italic toggle="yes">L</italic><sup>2</sup>/(2<italic toggle="yes">n</italic> + 1), which is assigned to the one-dimensional model for a particle in a potential energy box (see text).</p></caption><graphic id="gr8" xlink:href="jp-2007-12068f_0009.tif" position="float" orientation="portrait"></graphic></fig><p>Worth special note is the fact that the slopes of the fitted solvatochromic curves increase significantly with increasing chain length (see Table <xref rid="tbl2"></xref> and Figure <xref rid="fig7"></xref>). As can clearly be seen from Figure <xref rid="fig7"></xref>, the solvatochromism of the studied polyenes increases linearly with the increasing length of their chain, as expected.</p><fig id="fig7" position="float" orientation="portrait"><label>7</label><caption><p>Variation of the solvatochromic sensitivity of ttbPn (see Table <xref rid="tbl2"></xref>) with the length of the polyene chain.</p></caption><graphic id="gr9" xlink:href="jp-2007-12068f_0001.tif" position="float" orientation="portrait"></graphic></fig><p>Essentially identical conclusions can be drawn by expressing the solvent polarizability in terms of (<italic toggle="yes">n</italic><sup>2</sup> − 1)/(<italic toggle="yes">n</italic><sup>2</sup> + 2) instead of the empirical SP values used. Table <xref rid="tbl2"></xref> shows the results for the corresponding fitted curves. The sole difference from the previous ones is that the fitting was somewhat poorer than with SP. Thus, <italic toggle="yes">r</italic> was in the region of 0.96 and the errors significantly greater. On the other hand, the predictions for the gas phase were quite good but subject to higher uncertainty for ttbP3 (34341 ± 166 cm<sup>−1</sup>) and ttbP4 (31245 ± 190 cm<sup>−1</sup>). The solvatochromic slopes also increased with increasing chain length (see Table <xref rid="tbl2"></xref>). Such slopes were considerably smaller than those for unsubstituted polyenes. At this point, one may wonder whether the sensitivity of the different polyenes to the solvent polarizability is shared by the polyene structure, in which case, the slopes of the corresponding <italic toggle="yes">v</italic> versus polarizability plots should be identical for all polyene derivatives; otherwise, they would reflect the intrinsic variation of polarizability with electronic excitation, Δα,<xref rid="ref10" ref-type="bibr"></xref> and be proportional to Δα for the polyene type. One further question is whether the solvatochromic slope may also be influenced by some interaction between the substituent and solvent.</p><p>By way of example, let us focus on the solvatochromic behavior of octatetraenes. In 1977, Sklar et al.<xref rid="ref6" ref-type="bibr"></xref> found the absorption maximum for the 1Ag → 1Bu transition in α,ω-diphenyloctatetraene to vary linearly as a function of the solvent polarizability, with a slope of −10900 ± 1000 cm<sup>−1</sup>. In 1978, Gavin et al.<xref rid="ref5" ref-type="bibr"></xref> showed that the 0−0 component for the 1Ag → 1Bu transition in octatetraene in ten different solvents also varied linearly with solvent polarizability, with a slope of −10909 ± 1000 cm<sup>−1</sup>. These results suggest that the slope is insensitive to the polarizability change in the octatetraene and hence that the slope for the phenylated octatetraene should be greater than that for unsubstituted octatetraene. However, in 1978, Andrews <xref rid="ref20" ref-type="bibr"></xref> showed α,ω-dimethyloctatetraene to exhibit a slope of −10150 ± 150 cm<sup>−1</sup> against the solvent polarizability. At most, such a slope can be assimilated to that for unsubstituted octatetraene; more probably, however, it is smaller because, on the basis of its Δα value, it should exceed that for octatetraene. Recently, our group measured the solvatochromism of ttbP4,<xref rid="ref17" ref-type="bibr"></xref> which has a Δα value between those for octatetraene and α,ω-diphenyloctatetraene, and found a slope of only −8049 ± 772 cm<sup>−1</sup>, which is markedly smaller than even that for octatetraene. These results can be ascribed to alkyl substituents, hindering access of solvent molecules to the polyene system and reducing its solvatochromism via the solvent polarizability as a result. Also, they warrant further investigation, which, however, should be conducted by the same group, using an appropriate body of methyl and <italic toggle="yes">tert</italic>-butyl derivatives of the same polyene structure.</p></sec></sec><sec id="sec4"><title>Conclusions</title><p><italic toggle="yes">All</italic>-<italic toggle="yes">trans</italic>-polyenes exhibit a strong absorption band for their 1Ag → 1Bu transition that is red-shifted as the polarizability of the medium increases. The transition, however, is insensitive to other properties of the medium such as dipolarity, acidity of basicity. The sensitivity of the transition to the polarizability of the medium increases linearly with increasing length of the polyene chain.</p></sec></body><back><ack><title>Acknowledgments</title><p>J.C. is grateful to Spain’s DGICyT for funding this work through Project CTQ2005-03053.</p></ack><ref-list><title>References</title><ref id="ref1"><mixed-citation publication-type="book" id="cit1"><person-group person-group-type="allauthors"><name name-style="western"><surname>Abrahamson</surname><given-names>W.</given-names></name>, <name name-style="western"><surname>Ostroy</surname><given-names>S. E.</given-names></name></person-group> The photochemical macromolecular aspects of vision. In <source>Progress in Biophysics and Molecular Biology</source>; <person-group person-group-type="editor"><name name-style="western"><surname>Butler</surname><given-names>J. A.</given-names></name>, <name name-style="western"><surname>Huxley</surname><given-names>H. 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Jones (Technical University of Braunschweig) and will be reprted in detail in our full paper on the preparation of these hydrocarbons; ref <xref specific-use="ref-style=base-text" rid="ref10" ref-type="bibr"></xref></comment>.</mixed-citation></ref><ref id="ref20"><mixed-citation id="cit20"><person-group person-group-type="author"><name name-style="western"><surname>Andrews</surname><given-names>J.</given-names></name></person-group> <comment>Thesis, Stanford University, Stanford, California</comment>, <year>1978</year>.</mixed-citation></ref></ref-list></back></article></istex:document></istex:metadataXml><mods version="3.6"><titleInfo><title>On the Photophysics of Polyenes. 1. Bathochromic Shifts in Their 1Ag → 1Bu Electronic Transitions Caused by the Polarizability of the Medium</title></titleInfo><titleInfo type="abbreviated"><title>Photophysics of Polyenes</title></titleInfo><name type="personal" displayLabel="corresp"><namePart type="family">CATALÁN</namePart><namePart type="given">Javier</namePart><affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</affiliation><affiliation>E-mail: javier.catalan@uam.es</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="family">HOPF</namePart><namePart type="given">Henning</namePart><affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="family">KLEIN</namePart><namePart type="given">Dagmar</namePart><affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="family">MARTUS</namePart><namePart type="given">Meinrad</namePart><affiliation>Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain, and Institut für Organische Chemie, Technische Universität, D-38106 Braunschweig, Germany</affiliation><role><roleTerm type="text">author</roleTerm></role></name><typeOfResource>text</typeOfResource><genre type="research-article" displayLabel="Article" authority="ISTEX" authorityURI="https://content-type.data.istex.fr" valueURI="https://content-type.data.istex.fr/ark:/67375/XTP-1JC4F85T-7">research-article</genre><originInfo><publisher>American Chemical Society</publisher><dateCreated encoding="w3cdtf">2008-05-30</dateCreated><dateIssued encoding="w3cdtf">2008-06-26</dateIssued><copyrightDate encoding="w3cdtf">2008</copyrightDate></originInfo><abstract>As shown in this study, the solvatochromic behavior of polyenes depends exclusively on the polarizability of the medium and, even more interestingly, their solvatochromism increases markedly with increasing length of the polyene chain. By virtue of the electronic nature of the interaction of polyenes with the medium, their solvatochromic response to a polarizability change is instantaneous, making these compounds extremely effective polarizability probes for molecular environments. The extreme sensitivity of polyenes to the polarizability of their environment is consistent with the fact that changes in molecular architecture such as those occurring in photosynthetic systems can give rise to polarizability gradients resulting in red shifts in the 1Ag → 1Bu transition, thereby opening up new channels directing the energy transfer involved to energy trapping sites in such systems.</abstract><relatedItem type="host"><titleInfo><title>The Journal of Physical Chemistry A</title></titleInfo><titleInfo type="abbreviated"><title>J. Phys. Chem. A</title></titleInfo><genre type="journal" authority="ISTEX" authorityURI="https://publication-type.data.istex.fr" valueURI="https://publication-type.data.istex.fr/ark:/67375/JMC-0GLKJH51-B">journal</genre><identifier type="ISSN">1089-5639</identifier><identifier type="eISSN">1520-5215</identifier><identifier type="acspubs">jx</identifier><identifier type="coden">JPCAFH</identifier><part><date>2008</date><detail type="volume"><caption>vol.</caption><number>112</number></detail><detail type="issue"><caption>no.</caption><number>25</number></detail><extent unit="pages"><start>5653</start><end>5657</end></extent></part></relatedItem><identifier type="istex">FC3122FD255311FC236EDDE88A53120D5A5BC332</identifier><identifier type="ark">ark:/67375/TPS-8697FC7D-6</identifier><identifier type="DOI">10.1021/jp712068f</identifier><accessCondition type="use and reproduction" contentType="restricted">Copyright © 2008 American Chemical Society</accessCondition><recordInfo><recordContentSource authority="ISTEX" authorityURI="https://loaded-corpus.data.istex.fr" valueURI="https://loaded-corpus.data.istex.fr/ark:/67375/XBH-X5HBJWF8-J">ACS</recordContentSource><recordOrigin>Copyright © 2008 American Chemical Society</recordOrigin></recordInfo></mods><json:item><extension>json</extension><original>false</original><mimetype>application/json</mimetype><uri>https://api.istex.fr/ark:/67375/TPS-8697FC7D-6/record.json</uri></json:item></metadata><annexes><json:item><extension>tiff</extension><original>true</original><mimetype>image/tiff</mimetype><uri>https://api.istex.fr/document/FC3122FD255311FC236EDDE88A53120D5A5BC332/annexes/tiff</uri></json:item></annexes><serie></serie></istex></record>Pour manipuler ce document sous Unix (Dilib)
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