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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Investigation of the S-1/ICT - S-0 internal conversion lifetime of 4 '-apo-beta-caroten-4 '-al and 8 '-apo-beta-caroten-8 '-al: Dependence on conjugation length and solvent polarity
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Investigation of the S-1/ICT - S-0 internal conversion lifetime of 4 '-apo-beta-caroten-4 '-al and 8 '-apo-beta-caroten-8 '-al: Dependence on conjugation length and solvent polarity

机译：4'-apo-beta-caroten-4'-al和8'-apo-beta-caroten-8'-al的S-1 / ICT-> S-0内部转换寿命的研究：对共轭长度和溶剂极性

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摘要

The ultrafast internal conversion (IC) dynamics of aldehyde-substituted apocarotenoids (n'-apo-beta-caroten-n'-als with n = 4, 8 and 12) have been investigated in a systematic variation of conjugation length and solvent polarity using time-resolved femtosecond transient absorption spectroscopy. After excitation to the S-2 state with different excess energies, the subsequent intramolecular dynamics were investigated at several probe wavelengths covering the S-0 -> S-2 and S-1/ICT -> S-n absorption bands. Time constants tau(1) for the internal conversion process S-1/ICT -> S-0 of 4'-apo-beta-caroten-4'-al and 8'-apo-beta-caroten-8'-al have been newly measured. We compared these results with our earlier measurements for 12'-apo-beta-caroten-12'-al (D.A. Wild, K. Winkler, S. Stalke, K. Oum, T. Lenzer Phys. Chem. Chem. Phys. 2006, 8, 2499). In the case of the aldehyde with the longest conjugation (4'-apo-beta-caroten-4'-al), tau(1) is almost independent of solvent polarity (4-5 ps), whereas a significant reduction of tau(1) from 22.7 to 8.6 ps for the shorter 8'-apo-beta-caroten-8'-al and an even more pronounced reduction from 220 to 8.0 ps for 12'-apo-beta-caroten-12'-al were observed when the solvent medium was changed from n-hexane to methanol, respectively. In n-hexane, tau(1) of the apocarotenals is strongly dependent on the conjugation length and this can be well understood in terms of an energy gap law description where the S-1-S-0 energy differences were estimated from their steady-state fluorescence spectra. In highly polar solvents, the IC to S-0 is very fast, irrespective of the conjugation length. This is probably due to the stabilization of an intramolecular charge transfer (ICT) state in 12'-apo-beta-caroten-12'-al and 8'-apo-beta-caroten-8'-al. In the case of 4'-apo-beta-caroten-4'-al, such an influence of an ICT state is presumably less important than for the other two apocarotenals.
机译：使用共轭长度和溶剂极性的系统变化，研究了醛取代的类胡萝卜素（n'-apo-β-胡萝卜素-n'-als，n = 4、8和12）的超快内部转化（IC）动力学。时间分辨飞秒瞬态吸收光谱。在以不同的过剩能量激发到S-2状态后，在覆盖S-0-> S-2和S-1 / ICT-> S-n吸收带的几个探针波长下研究了随后的分子内动力学。内部转换过程S-1 / ICT-> S-0的4'-apo-beta-caroten-4'-al和8'-apo-beta-caroten-8'-al的时间常数tau（1）具有被重新测量。我们将这些结果与我们之前对12'-apo-beta-caroten-12'-al的测量结果进行了比较（DA Wild，K。Winkler，S。Stalke，K。Oum，T。Lenzer Phys。Chem。Chem。Phys。2006 ，8，2499）。对于结合时间最长的醛（4'-apo-β-caroten-4'-al），tau（1）几乎与溶剂极性无关（4-5 ps），而tau（ 1）较短的8'-apo-beta-caroten-8'-al从22.7 ps下降到8.6 ps，观察到12'-apo-beta-caroten-12'-al从220 ps降至8.0 ps更为明显当溶剂介质分别从正己烷变为甲醇时。在正己烷中，aaucarotenal的tau（1）强烈依赖于结合长度，这可以通过能隙定律描述很好地理解，其中S-1-S-0能量差是根据它们的稳态估计的。状态荧光光谱。在高极性溶剂中，与共轭长度无关，S-0的IC非常快。这可能是由于12'-apo-β-胡萝卜素-12'-al和8'-apo-β-胡萝卜素-8'-al中分子内电荷转移（ICT）状态的稳定所致。对于4'-apo-beta-caroten-4'-al而言，ICT状态的影响可能不如其他两个Apodototenals重要。

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