Seki Soichiro, Yoshida Kazuhiro, Sugisaki Mitsuru, Yamano Nami, Fujii Ritsuko
Graduate School of Science, Osaka Metropolitan University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan.
Key Laboratory of Advanced Light Conversion Materials and Biophotonics, Department of Chemistry, Renmin University of China, Beijing 100872, P. R. China.
J Phys Chem B. 2024 Jun 13;128(23):5623-5629. doi: 10.1021/acs.jpcb.4c02212. Epub 2024 Jun 4.
The versatile functions of carotenoids in biological systems are associated with the extended π-electron conjugation system. Strong visible absorption resulting from the optically allowed S (1B) state and the low-lying optically forbidden S (2A) state examined. Carotenoids also exhibit an absorption band in the ultraviolet-B region; however, the origin of this band (hereafter referred to as S state) is not well characterized. The S state is a candidate for the destination level of the well-known S → S transient absorption; however, an obvious energy mismatch has been observed. In this study, we examined the steady-state and picosecond transient absorption spectra of lycopene in various solvents. The S absorption of carotenoids with diverse conjugation lengths was also examined. The dependence of the energies on solvent polarizability and conjugation length revealed that both S and S are the "second" B state. The absorption spectrum for lycopene at 200 K revealed an additional vibrational band, which may be the vibrational origin of the S → S band. Considering the slow vibrational relaxation of the 2A state, the S → S transition may represent the 2A ( = 1) → 2B ( = 0) transition, and the energetic contradiction can be resolved.
类胡萝卜素在生物系统中的多种功能与扩展的π电子共轭体系有关。研究了由光学允许的S(1B)态和低位光学禁阻的S(2A)态产生的强烈可见光吸收。类胡萝卜素在紫外-B区域也表现出一个吸收带；然而，该吸收带（以下称为S态）的起源尚未得到很好的表征。S态是著名的S→S瞬态吸收的终态候选者；然而，已经观察到明显的能量不匹配。在本研究中，我们研究了番茄红素在各种溶剂中的稳态和皮秒瞬态吸收光谱。还研究了具有不同共轭长度的类胡萝卜素的S吸收。能量对溶剂极化率和共轭长度的依赖性表明，S和S都是“第二”B态。200K下番茄红素的吸收光谱显示出一个额外的振动带，这可能是S→S带的振动起源。考虑到2A态的缓慢振动弛豫，S→S跃迁可能代表2A(=1)→2B(=0)跃迁，并且能量矛盾可以得到解决。
