紫细菌捕光天线LH2中的超快光物理研究

采用飞秒泵浦探测技术研究了紫细菌外周捕光天线LH2中的超快光动力学过程.从B800蓝侧的激发态动力学中观察到B800到B850的能量传递时间,实验结果与理论计算结果的差别说明激发B800时可能引起B850上激子带的直接激发,或存在由B800到B850上激子态的能量传递通道.在B800红侧激发的动力学过程中,漂白信号前端存在的一个快速光吸收信号主要来源于B850上激子带的直接激发.在天然RS601和突变体GM309的LH2中,800 nm激发时的动力学过程都表现为一个类似的光漂白过程,动力学曲线的衰减时间常量在天然LH2中明显快于突变体中,说明在GM309中B800到B850的激发能传递速率有所降低.而在845 nm激发下两个样品中的快过程类似,但慢过程在GM309中有所增快,激发态中的能量重新分布包括逆向的能量传递也受到类胡萝卜素微结构的影响.

Ultrafast Photophysical Properties of Light-harvesting Complexes (LH2) in Purple Bacteria

The ultrafast photophysical processes in light-harvesting complex LH2 in purple bacteria are investigated by using femtosecond pump-probe technique.With the excitation wavelength at blue side of B800 absorption band,a hundred of femtosecond decay component is observed,which can be ascribed to the energy transfer from B800 to B850.The obtained result is not consistent with the Frster energy mechanism,which implies there is an additional energy transfer process via upper exciton band of B850.Under the excitation wavelength at red side of B800 absorption band,there is a fast excited state absorption before photo-bleaching,originating from the direct excitation of upper excitonic levels of B850 molecules.From the kinetic traces of RS601 and GM309 with 800 nm excitation,the energy transfer from B800 to B850 is slow down in GM309.With 845 nm excitation,the energy redistribution in excited state of B850 in GM309 is faster than that in RS601.These results indicate the structural change of carotenoid affects the excitation relaxation of pigments and energy transfer between in LH2.