Spectroscopic study on specific intermolecular interactions in aromatic biomolecules in the isolated state.

用频域和时间域测量方法研究了超音速喷流膨胀中氢键分子的结构和激发态动力学。我们测量了氢键7-氮杂环己烷二聚体的不同氢化异构体的烧孔光谱。光谱表明，7-氮杂环二聚体最低激发态的激子共振相互作用应视为激子理论的弱耦合极限。烧孔光谱表明，在Zewail小组的飞秒时间分辨实验中，激发了短寿命和长寿命的振动态，提供了双指数衰变曲线。双指数衰减曲线是阶跃激发态双质子转移(ESDPT)的有力证据。然而，我们发现皮秒脉冲激发的衰变曲线可以用单指数函数来拟合。这一结果清楚地表明，ESDPT是通过协同机制发生的。分散的Fluo…测量了7-氮杂环己烷二聚体的荧光光谱。发现了H/D同位素对反应速率的显著影响。发现了ESDPT反应的协作性，并研究了取代对ESDPT反应的影响。7-氮杂环己烷3-位上的甲基取代对ESDPT速率没有影响，但由于分子间氢键的减弱，4-位上的氯原子或二甲氨基的取代显著降低了ESDPT速率。我们还测量了中性和离子状态下的各种氢键簇合物，探讨了结构与动力学的关系。例如，我们研究了7-氮杂环-(H_2O)_n(n=1-3)的激发态质子转移。Castleman等人之前的报告。飞秒光谱结果表明，7-氮杂环己烷-(H_20)_n(n=2-4)发生了激发态质子转移。而7-氮杂环己烷-(H_2O)_n(n=1-3)则未观察到红移荧光，表明激发态质子转移受到抑制。较少

Structures and the excited-state dynamics of hydrogen bonded molecules in supersonic jet expansion have been studied by both the frequency domain and time-domain measurements. We have measured hole-burning spectra of various deuterated isotomers of the hydrogen bonded 7-azaindole dimer. The spectra show that the exciton resonance interaction in the lowest excited state of the 7-azaindole dimer should be treated as a weak coupling limit of the exciton theory. The hole-burning spectra suggest that the vibronic states with short and long lifetimes are excited in the femtosecond time-resolved experiments by Zewail's group, providing bi-exponential decay profiles. The biexponential decay profiles had been a strong evidence of the stepwise excited-state double-proton transfer (ESDPT). However, we have found that the decay profiles excited by picoseond pulse are fitted with single-exponential functions. This result clearly shows that ESDPT occurs by the concerted mechanism. The dispersed fluo … More rescence spectra are measured for the undeuterated and deuterated 7-azaindole dimers. A remarkable H/D isotope effects on the reaction rate has been detected. We have found a cooperative nature of the ESDPT reaction.The effect of substitution on the ESDPT reaction has also been studied. The substitution of the methyl group at the 3-position of the 7-azaindole does not affect the ESDPT rate, but the substitution of the Cl atom or the dimethylamino group at the 4-position significantly decrease the ESDPT rate due to the weakening of the intermolecular hydrogen-bonds.We also measured various hydrogen bonded clusters in the neutral and ionic states to investigate the relation between the structure and dynamics. For example, we have examined the excited-state proton transfer of the 7-azaindole-(H_2O)_n(n=1-3). Previous report by Castleman et al. with femtosecond spectroscopy concluded that the excited-state proton transfer occurs in 7-azaindole-(H_20)_n(n=2-4). However, no red-shifted fluorescence has been observed in 7-azaindole-(H_2O)_n(n=1-3), indicating that the excited-state proton transfer is inhibited. Less