Kopczynski Matthäus, Lenzer Thomas, Oum Kawon, Seehusen Jaane, Seidel Marco T, Ushakov Vladimir G
Institut für Physikalische Chemie, Universität Göttingen, Tammannstrasse 6, D-37077 Göttingen, Germany.
Phys Chem Chem Phys. 2005 Jul 21;7(14):2793-803. doi: 10.1039/b506574g. Epub 2005 Jun 21.
The ultrafast internal conversion (IC) dynamics of seven C(40) carotenoids have been investigated at room temperature in a variety of solvents using two-color transient lens (TL) pump-probe spectroscopy. We provide comprehensive data sets for the carbonyl carotenoids canthaxanthin, astaxanthin, and-for the first time-echinenone, as well as new data for lycopene, beta-carotene, (3R,3'R)-zeaxanthin and (3R,3'R,6'R)-lutein in solvents which have not yet been investigated in the literature. Measurements were carried out to determine, how the IC processes are influenced by the conjugation length of the carotenoids, additional substituents and the polarity of the solvent. TL signals were recorded at 800 nm following excitation into the high energy edge of the carotenoid S2 band at 400 nm. For the S2 lifetime solvent-independent upper limits on the order of 100-200 fs are estimated for all carotenoids studied. The S1 lifetimes are in the picosecond range and increase systematically with decreasing conjugation length. For instance, in the sequence canthaxanthin/echinenone/beta-carotene (13/12/11 double bonds) one finds tau1 approximately 5, 7.7 and 9 ps for the S1-->S0 IC process, respectively. Hydroxyl groups not attached to the conjugated system have no apparent influence on tau1, as observed for canthaxanthin/astaxanthin (tau1 approximately 5 ps in both cases). For all carotenoids studied, tau1 is found to be insensitive to the solvent polarity. This is particularly interesting in the case of echinenone, canthaxanthin and astaxanthin, because earlier measurements for other carbonyl carotenoids like, e.g., peridinin partly showed dramatic differences. The likely presence of an intramolecular charge transfer state in the excited state manifold of C40 carbonyl carotenoids, which is stabilized in polar solvents, has obviously no influence on the measured tau1.
利用双色瞬态透镜（TL）泵浦 - 探测光谱技术，在室温下于多种溶剂中研究了七种C(40)类胡萝卜素的超快内转换（IC）动力学。我们提供了关于羰基类胡萝卜素角黄素、虾青素以及首次研究的海胆酮的全面数据集，同时还给出了番茄红素、β - 胡萝卜素、(3R,3'R) - 玉米黄质和(3R,3'R,6'R) - 叶黄素在文献中尚未研究过的溶剂中的新数据。进行测量以确定IC过程如何受到类胡萝卜素的共轭长度、额外取代基和溶剂极性的影响。在400 nm激发到类胡萝卜素S2带的高能边缘后，于800 nm记录TL信号。对于所研究的所有类胡萝卜素，估计S2寿命的溶剂无关上限约为100 - 200 fs。S1寿命处于皮秒范围内，并随着共轭长度的减小而系统地增加。例如，在角黄素/海胆酮/β - 胡萝卜素（13/12/11个双键）序列中，对于S1→S0 IC过程，分别发现τ1约为5、7.7和9 ps。未连接到共轭体系的羟基对τ1没有明显影响，如角黄素/虾青素的情况（两种情况下τ1均约为5 ps）。对于所研究的所有类胡萝卜素，发现τ1对溶剂极性不敏感。这在海胆酮、角黄素和虾青素的情况下尤其有趣，因为早期对其他羰基类胡萝卜素如多甲藻素的测量部分显示出显著差异。C40羰基类胡萝卜素激发态流形中可能存在的分子内电荷转移态，在极性溶剂中会稳定下来，但显然对测量的τ1没有影响。
