ROLE OF COHERENT PHENOMENA IN ULTRAFAST BIOLOGICAL PROCESSES

一个重要的问题是， 光驱动反应的初始步骤中的光激发是 在主要过程中保持或不保持 在反应面上最初形成的波包涉及相干 动议？相干波包传播的观测提供了 关于势能面性质的另一种探索 主要的动力过程正在发生。这个 一系列乙炔桥联化合物的光物理性质 研究了(Porphinato)锌(II)齐聚物 飞秒和皮秒时间尺度使用超快魔角和 偏振泵浦-探测光谱学。它们表现出快速(小于或 等于50ps)Soret之后发射态的形成 光激发，几乎比同类产品快一个数量级 对于单体，观察到1 ps S2？？S1的内部转化 含乙炔基团的(卟啉)锌(II)络合物 直接到它的大循环碳框架 [(5-trimethylsilylethynyl-10，20-diphenylporphinato)zinc(Ii)]。这个 飞秒和皮秒动力学强烈地受到 卟啉到卟啉的连接拓扑：如果是β-到β-乙炔 桥连接了两个(Porphinato)锌(II)部分，这保持了 发射态的x-y简并度，其动力学为 与弱偶联卟啉中的能量平衡一致 一对。相反，以中层到中层为特征系统 (卟啉)锌(II)单元间的乙炔桥联拓扑 表现出与显著的环间共轭一致的性质 以及(pi，pi*)激发态x-y简并度的损失。 总的来说，这些数据的稳态和时间分辨结果 介观到介观桥联体系暗示了一定程度的构象 溶液中基态结构的非均质性 在卟啉环的共轭程度方面不同； 这些构象在S1激发状态下在类似于 30ps时间刻度，以产生构象均匀、共面的 正在发射状态。

An important question is whether the coherence introduced by optical excitation in the initial step of a light driven reaction is maintained during the primary process or not Do the dynamics of the initially formed wavepacket on the reactive surface involve coherent motion? The observations of coherent wavepacket propagation provides an additional probe of the nature of the potential energy surface upon which the primary dynamical processes are occurring. The photophysical properties of a series of ethynyl-bridged (porphinato)zinc(II) oligomers have been investigated over the femtosecond and picosecond time scales using ultrafast magic angle and polarized pump-probe spectroscopy. They exhibit rapid (less than or equal to 50 fs) formation of the emitting state following Soret photoexcitation, nearly an order of magnitude faster than the similar to 1 ps S2 ??S1 internal conversion observed for a monomeric (porphinato)zinc(II) complex that bears an ethyne moiety fused directly to its macrocycle carbon framework [(5-trimethylsilylethynyl-10,20-diphenylporphinato)zinc (II)]. The femtosecond and picosecond dynamics are strongly influenced by the porphyrin-to-porphyrin linkage topology: if a beta-to-beta ethyne bridge links the two (porphinato)zinc(II) moieties, this maintains the x-y degeneracy of the emitting state, the dynamics of which are consistent with energy equilibration within a weakly coupled porphyrin pair. In contrast, systems whi ch feature a meso-to-meso ethynyl-bridged linkage topology between (porphinato)zinc(II) units exhibit properties consistent with significant inter-ring conjugation and loss of x-y degeneracy for the (pi, pi*) excited states. Collectively, the steady-state and time-resolved results for these meso-to-meso bridged systems suggest some degree of conformational heterogeneity for the ground state structures in solution, which differ with respect to the degree of conjugation of porphyrin rings; these conformers interconvert in the S1 excited state on a similar to 30 ps time scale to produce a conformationally uniform, coplanar emitting state.