Extremely strong solvent dependence of the S1→S0 internal conversion lifetime of 12′-apo-β-caroten-12′-al
Extremely strong solvent dependence of the S1→S0 internal conversion lifetime of 12′-apo-β-caroten-12′-al
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DOI：
10.1039/b601669c
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发表时间：
2006-01-01
影响因子：
3.3
通讯作者：
Lenzer, Thomas
中科院分区：
文献类型：
--
作者：
Wild, Duncan A.;Winkler, Kathrin;Lenzer, Thomas
利用时间分辨飞秒瞬态吸收光谱研究了羰基类胡萝卜素12 '-apo-beta-caroten-12'-al在不同极性溶剂中的超快内转换动力学。用390或470 nm的泵浦光将分子激发到S-2态。随后在覆盖S-0 -> S-2和S-1 -> S-n带的几个探针波长处检测到分子内动力学。对于S-1 -> S-0内转换过程，发现随着极性的增加，有一个明显的加速过程，即：S-1 → S-0;例如，在一个实施例中，在390 nm激发后τ（1）的寿命= 220 ps（正己烷）、91 ps（四氢呋喃）和8.0 ps（甲醇）。观察可以合理化的形成组合的S-1/ICT（分子内电荷转移）状态中的极性更强的溶剂。这种作用甚至比文献中报道的多甲藻素的最强作用还要强。向12 ′-apo-beta-caroten-12 ′-al的乙醇溶液中加入锂盐仅导致IC时间常数τ（1）的微小变化。此外，我们估计在所有溶剂中S-2 -> S-1内转换过程的时间常数τ（2）的上限为300 fs。
The ultrafast internal conversion (IC) dynamics of the carbonyl carotenoid 12'-apo-beta-caroten-12'-al has been investigated in solvents of varying polarity using time-resolved femtosecond transient absorption spectroscopy. The molecules were excited to the S-2 state by a pump beam of either 390 or 470 nm. The subsequent intramolecular dynamics were detected at several probe wavelengths covering the S-0 -> S-2 and S-1 -> S-n bands. For the S-1 -> S-0 internal conversion process, a remarkably strong acceleration with increasing polarity was found, e. g., lifetimes of tau(1) = 220 ps (n-hexane), 91 ps (tetrahydrofuran) and 8.0 ps (methanol) after excitation at 390 nm. The observation can be rationalized by the formation of a combined S-1/ICT ( intramolecular charge transfer) state in the more polar solvents. The effect is even stronger than the strongest one reported so far in the literature for peridinin. Addition of lithium salts to a solution of 12'-apo-beta-caroten- 12'-al in ethanol leads only to small changes of the IC time constant tau(1). In addition, we estimate an upper limit for the time constant tau(2) of the S-2 -> S-1 internal conversion process of 300 fs in all solvents.