Savikhin S, Struve W S
Ames Laboratory, U. S. Department of Energy, Ames, Iowa.
Biophys J. 1994 Nov;67(5):2002-7. doi: 10.1016/S0006-3495(94)80683-6.
One- and two-color absorption difference profiles were obtained for BChl a in 1-propanol with approximately 50-fs resolution, using a self-mode-locked Ti:sapphire laser system. Time evolution in the BChl a absorption difference spectrum produces nonexponential photobleaching/stimulated emission (PB/SE) decay kinetics in 800-nm one-color experiments. Nonexponential PB/SE rise behavior occurs for some combinations of pump and probe wavelengths in two-color experiments. Optimized parameters from triexponential fits to the absorption difference profiles depend markedly on the fitting time window; they typically include a minor component with lifetime in the hundreds of fs. Much of the latter component is due to vibrational relaxation and/or intramolecular vibrational redistribution, rather than solvent dielectric relaxation. Measurements of the pump-probe anisotropy indicate that the electronic transition moment for the broad Qy excited state absorption band that overlaps the Qy steady-state absorption spectrum makes an angle of at most 20 degrees from that of the ground-->Qy state transition. No coherent oscillations are observed at early times. Our results bear directly on the interpretation of fs pump-probe experiments on BChl a-containing pigment-protein complexes.
使用自锁模钛宝石激光系统，以约50飞秒的分辨率获得了1-丙醇中细菌叶绿素a（BChl a）的单色和双色吸收差异谱。在800纳米单色实验中，BChl a吸收差异光谱中的时间演化产生非指数光漂白/受激发射（PB/SE）衰减动力学。在双色实验中，对于某些泵浦和探测波长的组合，会出现非指数PB/SE上升行为。对吸收差异谱进行三指数拟合得到的优化参数明显取决于拟合时间窗口；它们通常包括一个寿命在数百飞秒的次要成分。后一种成分的大部分是由于振动弛豫和/或分子内振动重新分布，而不是溶剂介电弛豫。泵浦-探测各向异性的测量表明，与Qy稳态吸收光谱重叠的宽Qy激发态吸收带的电子跃迁矩与基态→Qy态跃迁的电子跃迁矩的夹角至多为20度。在早期没有观察到相干振荡。我们的结果直接关系到对含BChl a的色素-蛋白质复合物进行飞秒泵浦-探测实验的解释。
