Ultrafast Dynamics of Long Homologues of Carotenoid Zeaxanthin
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- 作者：Hristina Staleva ; Muhammad Zeeshan ; Pavel Ch谩bera ; Vassilia Partali ; Hans-Richard Sliwka ; Tom谩拧 Pol铆vka
- 刊名：Journal of Physical Chemistry A
- 出版年：2015
- 出版时间：November 19, 2015
- 年：2015
- 卷：119
- 期：46
- 页码：11304-11312
- 全文大小：508K
- ISSN：1520-5215
文摘
Three zeaxanthin homologues with conjugation lengths N of 15, 19, and 23 denoted as Z15, Z19, and Z23 were studied by femtosecond transient absorption spectroscopy, and the results were compared to those obtained for zeaxanthin (Z11). The energies of S2 decrease from 20鈥?50 cm鈥? (Z11) to 18鈥?80 cm鈥? (Z15), 17鈥?95 cm鈥? (Z19), and 16鈥?60 cm鈥? (Z23). Fitting the N dependence of the S2 energies allowed the estimation of , the S2 energy of a hypothetical infinite zeaxanthin, to be 鈭?4鈥?00 cm鈥?. Exciting the 0鈥? band of the S2 state produces characteristic S1鈥揝n spectral profiles in transient absorption spectra with maxima at 556 nm (Z11), 630 nm (Z15), 690 nm (Z19), and 740 nm (Z23). The red shift of the S1鈥揝n transition with increasing conjugation length is caused by a decrease in the S1 state energy, resulting in S1 lifetimes of 9 ps (Z11), 0.9 ps (Z15), 0.35 ps (Z19), and 0.19 ps (Z23). Essentially the same lifetimes were obtained after excess energy excitation at 400 nm, but S1鈥揝n becomes broader, indicating a larger conformation disorder in the S1 state after 400 nm excitation compared to excitation into the 0鈥? band of the S2 state. An S* signal was observed in all samples, but only for Z15, Z19, and Z23 does the S* signal decay with a lifetime different from that of the S1 state. The S* lifetimes are 2.9 and 1.6 ps for Z15 and Z19, respectively. In Z23 the S* signal needs two decay components yielding lifetimes of 0.24 and 2.3 ps. The S* signal is more pronounced after 400 nm excitation.