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Titolo:
SINGLET-STATE CIS,TRANS PHOTOISOMERIZATION AND INTERSYSTEM CROSSING OF 1-ARYLPROPENES
Autore:
LEWIS FD; BASSANI DM; CALDWELL RA; UNETT DJ;
Indirizzi:
NORTHWESTERN UNIV,DEPT CHEM EVANSTON IL 60208 UNIV TEXAS,DEPT CHEM RICHARDSON TX 75083
Titolo Testata:
Journal of the American Chemical Society
fascicolo: 23, volume: 116, anno: 1994,
pagine: 10477 - 10485
SICI:
0002-7863(1994)116:23<10477:SCPAIC>2.0.ZU;2-H
Fonte:
ISI
Lingua:
ENG
Soggetto:
TRANSITION-METAL COMPLEXES; JET-COOLED STYRENE; PHOTOACOUSTIC CALORIMETRY; INTERMEDIATE NEGLECT; AROMATIC ALKENES; ISOMERIZATION; FLUORESCENCE; DYNAMICS; STILBENE; SPECTRA;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
43
Recensione:
Indirizzi per estratti:
Citazione:
F.D. Lewis et al., "SINGLET-STATE CIS,TRANS PHOTOISOMERIZATION AND INTERSYSTEM CROSSING OF 1-ARYLPROPENES", Journal of the American Chemical Society, 116(23), 1994, pp. 10477-10485

Abstract

The temperature dependence of the singlet state lifetime and photoisomerization and fluorescence quantum yields for trans- and cis-1-phenylpropene have been determined in hexane solution. Calculated barriers for twisting about the double bond on the singlet potential energy surface are 8.8 and 4.6 kcal/mol for the trans and cis isomer, respectively. The barrier for the trans isomer is sufficiently high to prevent isomerization on the singlet state surface at or below room temperature. However, isomerization occurs at low temperatures as a consequence ofintersystem crossing to the triplet state, which undergoes barrierless isomerization. The quantum yield for intersystem crossing, as determined by time-resolved photoacoustic calorimetry, is 0.60 +/- 0.03 and the rate constant for intersystem crossing is 4.7 x 10(7) s(-1). Whileinternal conversion is not significant at or below room temperature, thermally activated internal conversion competes with singlet isomerization at high temperatures. The cis isomer undergoes isomerization predominantly via the singlet state at room temperature. Both electron-donating (p-methoxy) and electron-withdrawing (m- and p-cyano, p-carbomethoxy, and p-trifluormethyl) aromatic substituents are found to lower the barrier for singlet state isomerization. Increased solvent polarity (acetonitrile vs hexane) results in variable decreases in the barrier for singlet state isomerization. Photoisomerization of the p-cyano derivative at room temperature occurs predominantly via the triplet state in hexane solution and via the singlet state in acetonitrile solution. The effects of substituents and solvent are better correlated withthe magnitude of the S-2-S-1 energy gap than the stability of either zwitterionic or biradical intermediates. Rate constants for intersystem crossing are, in most cases, not highly dependent upon aromatic substitution or solvent polarity.

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Documento generato il 02/12/20 alle ore 14:01:08