Abstract：
Using femtosecond differential spectroscopy, excitation energy transfer in reaction centers (RCs) of the carotenoidless strain of purple bacteria Rhodospirillum rubrum G9 was studied at room temperature. Excitation and probing of the Qy, Qx and Soret absorption bands of the RCs were carried out by pulses with duration of 25-30 fs. Modeling of ΔA (light - dark) kinetics made it possible to estimate the characteristic time of various stages of excitation energy transformation. It is shown that the dynamics of the downhill energy flow in the RCs is determined both by the internal energy conversion Soret→ Qx → Qy in each cofactor and by the energy transfer H* → B* → P* (H - bacteriopheophytin, B - bacteriochlorophyll a, P - bacteriochlorophyll a dimer) between cofactors. The transfer of energy between the upper excited levels (Soret and Qx) of the cofactors accelerates its arrival to the lower exciton level of the P, from where charge separation begins. It turned out that all conversion and energy transfer processes occur within 40-160 fs: the conversion Soret → Qx occurs in 40-50 fs, the conversion Qx → Qy occurs in 100-140 fs, the transfer H* → B* has a time constant of 80-120 fs, and the transfer B* → P* has a time constant of 130-160 fs. The rate of energy transfer between the upper excited levels is close to the rate of transfer between Qy levels.
摘要：
使用飞秒差分光谱法，在室温下研究了紫色细菌RhodospirillumrubrumG9的无胡萝卜素菌株的反应中心（RC）的激发能量转移。QY的激发和探测，RC的Qx和Soret吸收带通过持续时间为25-30fs的脉冲进行。对ΔA（亮-暗）动力学进行建模，可以估算激发能量转换各个阶段的特征时间。表明，RC中下坡能量流的动力学既由每个辅因子中的内部能量转换Soret→Qx→Qy决定，也由能量转移H*→B*→P*决定（H-细菌叶绿素，B-细菌叶绿素a，P-细菌叶绿素a二聚体)在辅因子之间。辅因子的较高激发能级（Soret和Qx）之间的能量转移加速了其到达P的较低激子能级，从电荷分离开始的地方。事实证明，所有转换和能量转移过程都发生在40-160fs内：转换Soret→Qx发生在40-50fs内，转换Qx→Qy发生在100-140fs中，传递H*→B*的时间常数为80-120fs，并且转移B*→P*具有130-160fs的时间常数。上激发能级之间的能量转移速率接近Qy能级之间的转移速率。
