The Benzophenone S1(n,*) T1(n,
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- 作者：Sté ; phane Aloï ; se ; Cyril Ruckebusch ; Lionel Blanchet ; Julien Ré ; hault ; Guy Buntinx ; Jean-Pierre Huvenne
- 刊名：Journal of Physical Chemistry A
- 出版年：2008
- 出版时间：January 17, 2008
- 年：2008
- 卷：112
- 期：2
- 页码：224 - 231
- 全文大小：438K
- 年卷期：v.112,no.2(January 17, 2008)
- ISSN：1520-5215
文摘
The well-known benzophenone intersystem crossing from S1(n,
*) to T1(n,*) states, for which direct transitionis forbidden by El-Sayed rules, is reinvestigated by subpicosecond time-resolved absorption spectroscopyand effective data analysis for various excitation wavelengths and solvents. Multivariate curve resolutionalternating least-squares analysis is used to perform bilinear decomposition of the time-resolved spectra intopure spectra of overlapping transient species and their associated time-dependent concentrations. The resultssuggest the implication of an intermediate (IS) in the relaxation process of the S1 state. Therefore, a two stepkinetic model, S1 
IS T1, is successfully implemented as an additional constraint in the soft-modelingalgorithm. Although this intermediate, which has a spectrum similar to the one of T1(n,*) state, could beartificially induced by vibrational relaxation, it is tentatively assigned to a hot T1(n,*) triplet state. Twocharacteristic times are reported for the transition S1 IS and IS T1, ~6.5 ps and ~10 ps respectively,without any influence of the solvent. Moreover, an excitation wavelength effect is discovered suggesting theparticipation of unrelaxed singlet states in the overall process. To go further discussing the spectroscopicrelevancy of IS and to rationalize the expected involvement of the T2(,*) state, we also investigate4-methoxybenzophenone. For this neighboring molecule, triplet energy level is tunable through solvent polarityand a clear correlation is established between the intermediate resolved by multivariate data analysis and thepresence of a T2(,*) above the T1(n,*) triplet. It is therefore proposed that the benzophenone intermediatespecies is a T1(n,*) high vibrational level in interaction with T2(,*) state.
*) to T1(n,*) states, for which direct transitionis forbidden by El-Sayed rules, is reinvestigated by subpicosecond time-resolved absorption spectroscopyand effective data analysis for various excitation wavelengths and solvents. Multivariate curve resolutionalternating least-squares analysis is used to perform bilinear decomposition of the time-resolved spectra intopure spectra of overlapping transient species and their associated time-dependent concentrations. The resultssuggest the implication of an intermediate (IS) in the relaxation process of the S1 state. Therefore, a two stepkinetic model, S1 IS T1, is successfully implemented as an additional constraint in the soft-modelingalgorithm. Although this intermediate, which has a spectrum similar to the one of T1(n,*) state, could beartificially induced by vibrational relaxation, it is tentatively assigned to a hot T1(n,*) triplet state. Twocharacteristic times are reported for the transition S1 IS and IS T1, ~6.5 ps and ~10 ps respectively,without any influence of the solvent. Moreover, an excitation wavelength effect is discovered suggesting theparticipation of unrelaxed singlet states in the overall process. To go further discussing the spectroscopicrelevancy of IS and to rationalize the expected involvement of the T2(,*) state, we also investigate4-methoxybenzophenone. For this neighboring molecule, triplet energy level is tunable through solvent polarityand a clear correlation is established between the intermediate resolved by multivariate data analysis and thepresence of a T2(,*) above the T1(n,*) triplet. It is therefore proposed that the benzophenone intermediatespecies is a T1(n,*) high vibrational level in interaction with T2(,*) state.