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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Control of the Photophysical Properties of Polyatomic Molecules by Substitution and Solvation: The Second Excited Singlet State of Azulene
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Control of the Photophysical Properties of Polyatomic Molecules by Substitution and Solvation: The Second Excited Singlet State of Azulene

机译：通过取代和溶剂化控制多原子分子的光物理性质：Azulene的第二个激发单重态

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摘要

The UV-visible-near-IR absorption spectra, S_2 -> S_0 fluorescence quantum yields and S_2 fluorescence lifetimes of 1-fluoroazulene, 1,3-difluoroazulene, and several of their alkyl-substituted derivatives have been measured at room temperature in up to six solvents, benzene, dichloromethane, ethanol, acetonitrile, n-hexane, and perfluoro-n-hexane. The quantum yields (up to 0.2) and lifetimes (up to 9.5 ns) of the S_2 state of 1,3-difluoroazulene are exceptionally large-the largest ever reported for an upper excited singlet state of a polyatomic molecule with a closed-shell ground state. The nonradiative rate constants for the decay of the S_2 states of these molecules in these solvents and of azulene, 1,3-dichloroazulene and 1,3-dibromoazulene, determined previously, have been analyzed in terms of the weak coupling case of radiationaless transition theory. The data show that the nonradiative rate constants for the S_2 states of azulene, 1-fluoroazulene, and 1,3-difluoroazulene in the nonpolar solvents follow the log-linear relationship expected of the energy gap law, provided that S_2-S_1 internal conversion is assumed to dominate the decay mechanism. The same linear correlation is obtained, irrespective of whether #DELTA#E(S_2-S_1) is varied by solvatochromism or fluorine substitution. Substitution by alkyl groups increases the nonradiative decay rates by increasing the effective number of coupled states while the electronic coupling matrix element remains constant. Substitution at the 6-position by an isopropyl group increases the rate constant by a constant factor of 2.9; however, multiple substitution does not have a multiplicative effect. Substitution by chlorine or bromine increases the S_2 decay rates by enhancing the rate of intersystem crossing to the triplet manifold. The rate enhancement is semiquantitatively modeled by considering the effects of spin-orbit coupling of the halogen atoms.
机译：在室温下至室温下测量了1-氟腈，1,3-二氟腈及其几种烷基取代衍生物的UV-可见-近IR吸收光谱，S_2-> S_0荧光量子产率和S_2荧光寿命。六种溶剂，苯，二氯甲烷，乙醇，乙腈，正己烷和全氟正己烷。 1,3-二氟azulene的S_2态的量子产率（最高0.2）和寿命（最高9.5 ns）异常大，这是有报道的具有闭壳基的多原子分子的上激发单线态的最大州。根据无辐射过渡理论的弱耦合情况，分析了先前确定的这些分子在这些溶剂中以及azulene，1,3-dichloroazulene和1,3-dibromoazulene的S_2状态衰减的非辐射速率常数。 。数据表明，在非极性溶剂中，z，1-氟，和1,3-二氟az的S_2态的非辐射速率常数遵循能隙定律的对数线性关系，条件是S_2-S_1的内部转化为假设是主导衰变机制。无论＃DELTA＃E（S_2-S_1）是否因溶剂变色或氟取代而变化，都可获得相同的线性相关性。当电子耦合矩阵元素保持恒定时，烷基取代可通过增加耦合态的有效数目来增加非辐射衰变速率。异丙基取代6位可将速率常数增加2.9倍。但是，多重替换没有乘法作用。氯或溴取代可通过增加系统间交叉至三重态歧管的速率来提高S_2衰减速率。通过考虑卤素原子的自旋轨道耦合的影响，对速率提高进行半定量建模。

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