Femtosecond Spectroscopy of Primary Processes of Photoisomerizations in Rhodopsin and Retinoid Proteins

视紫红质等类视黄素与视网膜的视觉系统具有高灵敏度、低噪声和宽动态范围的特点，本研究在飞秒到皮秒的时间范围内研究了视紫红质的主要光异构化过程。利用500-570 nm波段的可调谐飞秒光脉冲构建了时间分辨光谱分析装置，利用自相位调制产生的波长选择的飞秒连续谱两级染料放大器获得可调谐脉冲。与前人的工作相比，该实验在时间分辨率上有了很大的提高。该系统的时间分辨率约为300fS，阐明了章鱼视紫红质激发态动力学的详细机理。在700 nm处的激发态吸收寿命约为140ps。初级视紫红质(Prime)是在400fs内产生的，其吸收光谱类似于Batho的吸收光谱，Prime更可能是Batho的非热态，在800 nm处观察到另一个态的增益，寿命为2-4ps。还研究了细菌视紫红质(BR)的类似物14-氟细菌视紫红质(14-F-BR)，以阐明电子结构与超快结构变化动力学之间的关系。吸光度的变化特征与BR非常相似。氟原子的引入不影响初始弛豫动力学，表明电子结构不是影响顺式异构化动力学的重要因素。

The visual systems with rhodopsin and other retinoid proteins with retinal have high sensitivity, low noise, and wide dynamic range, In this research, the primary processes of photoisomerization of rhodopsins have been investigated in femtosecond to picosecond time region.The time-resolved spectroscopy apparatus with using tunable femtosecond light pulses in the spectral region of 500-570nm region was constructed, The tunable pulses are obtained by using two-stage dye amplifiers of wavelengthselected femtosecond continuum generated by self-phase modulation. The experiment has improves the data dramatically in time resolution in comparison with previous works. The time resolution of the system is about 300 fs.The detailed mechanism of the excited state dynamics of octopus rhodopsin is clarified. The lifetime of the excited state absorption in 700 nm is about 140 fs. Primerhodopsin (Prime) is generated within 400 fs and the absorption spectrum resembles the spectrum of Bathorhodopsin (Batho), Prime is more likely unthermalized state of Batho, Another state is observed as a gain in the 800 nm region with 2-4 ps lifetime.An analog of bacteriorhodopsin (BR), 14-fluorobacteriorhodopsin (14-F-BR), was also investigated to clarify the relationship between the electric structure and the dynamics of ultrafast structure changes. The feature of the absorbance changes are quite similar to those of BR. The fact that an introduction of fluorine atom does not affect the primary relaxation dynamics indicates that the electronic structure is not an important factor for the dynamics of trans-cis isomerization.