Institute of Chemistry and the Farkas Center for Light Induced Processes, The Hebrew University, Jerusalem 91904, Israel.
J Phys Chem B. 2010 Mar 4;114(8):3038-45. doi: 10.1021/jp910845h.
Excited-state dynamics of xanthorhodopsin (XR) and of salinixanthin (SX) in ethanol were investigated by ultrafast pump-hyperspectral probe spectroscopy. Following excitation to the strongly allowed S(2) state of the SX chromophore, transient spectra were recorded photoselectively in the range 430-850 nm. Global kinetic analysis of these data shows the following. (1) Efficient energy transfer from S(2) of the SX in XR to its retinal moiety is verified here. The lifetime of S(2) in SX is, however, determined to be approximately 20 fs, much shorter than previously reported. (2) Branching ratios of excitation transfer from S(2) to S(1), to S*, and to retinal in XR are measured leading to species associated difference spectra (SADS) for all the states involved. Strong protein effects are detected on these branching probabilities. (3) S(1) and S* absorption bands in both systems exhibit anisotropy well below the expected r = 0.4, indicating an angle of approximately 25 degrees between the S(0) --> S(2) and S(1) --> S(n)/S* --> S(n) transition dipoles. The latter allows confident assignment of the debated S* absorption band to an excited state of SX, and not to "hot" S(0). In light of the extremely fast IC from S(2) to lower excited singlets, possible involvement of ballistic IC in SX, and of coherent energy transfer in XR, are discussed.
用超快泵浦-高光谱探针光谱法研究了乙醇中黄视蛋白（XR）和盐生黄质（SX）的激发态动力学。在激发到 SX 发色团的强允许 S(2)态后，在 430-850nm 的范围内选择性地记录瞬态光谱。对这些数据的全局动力学分析表明：(1) 在这里验证了从 XR 中 SX 的 S(2)到其视黄醛部分的有效能量转移。然而，SX 的 S(2)的寿命被确定为大约 20fs，比以前报道的要短得多。(2) 从 S(2)到 S(1)、S和 XR 中视黄醛的激发转移分支比被测量，导致所有涉及的状态的物种相关差谱(SADS)。在这些分支概率上检测到强烈的蛋白质效应。(3) 两种体系的 S(1)和 S吸收带在低于预期的 r=0.4 时表现出各向异性，表明 S(0)到 S(2)和 S(1)到 S(n)/S到 S(n)跃迁偶极子之间的角度约为 25 度。后者可以将有争议的 S吸收带自信地分配给 SX 的激发态，而不是“热”的 S(0)。鉴于从 S(2)到较低的激发单重态的超快 IC，可能涉及到 SX 中的弹道 IC 和 XR 中的相干能量转移，对此进行了讨论。
