Fingerhut Benjamin P, Dorfman Konstantin E, Mukamel Shaul
Chemistry Department, University of California, Irvine, California 92697-2025, USA.
J Phys Chem Lett. 2013 Jun 6;4(11):1933-1942. doi: 10.1021/jz400776r.
Resolving the excited state dynamics of DNA- and RNA- nucleobases has attracted considerably attention. UV irradiation of the isolated nucleobases leads to the population of an electronic excited state which is quenched by internal conversion mediated by conical intersections on an ultrafast timescale. We present non-adiabatic on-the-fly molecular dynamics simulations of the UV-pump-IR-probe signal of the pyrimidine nucleobase uracil using a novel semiclassical protocol which takes into account the path integral over the excited state vibrational dynamics and properly describes the joint temporal and spectral resolution of the technique. Simulations of vibrational motions of carbonyl fingerprint modes in the electronically excited states reveal clear signatures of different relaxation pathways on a timescale of hundreds of femtoseconds which arise from an ultrafast branching in the excited state. We show that the inherent temporal and spectral resolution of the technique is not purely instrumental but also depends on the vibrational fluctuation timescale.
解析DNA和RNA核碱基的激发态动力学已引起了相当大的关注。对分离出的核碱基进行紫外线照射会导致电子激发态的产生，该激发态会在超快时间尺度上通过锥形交叉介导的内转换而猝灭。我们使用一种新颖的半经典方法，对嘧啶核碱基尿嘧啶的紫外泵浦-红外探测信号进行了非绝热实时分子动力学模拟，该方法考虑了激发态振动动力学的路径积分，并恰当地描述了该技术的联合时间和光谱分辨率。对电子激发态中羰基指纹模式的振动运动模拟揭示了在数百飞秒时间尺度上不同弛豫途径的清晰特征，这些特征源于激发态中的超快分支。我们表明，该技术固有的时间和光谱分辨率并非纯粹由仪器决定，还取决于振动涨落时间尺度。
