Coe Joshua D, Martínez Todd J
Department of Chemistry, Beckman Institute, and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801.
J Phys Chem A. 2006 Jan 19;110(2):618-30. doi: 10.1021/jp0535339.
Excited-state potential energy surface (PES) characterization is carried out at the CASSCF and MRSDCI levels, followed by ab initio dynamics simulation of excited-state intramolecular proton transfer (ESIPT) on the S2(pipi*) state in malonaldehyde. The proton-transfer transition state lies close to an S2/S1 conical intersection, leading to substantial coupling of proton transfer with electronic relaxation. Proton exchange proceeds freely on S2, but its duration is limited by competition with twisting out of the molecular plane. This rotamerization pathway leads to an intersection of the three lowest singlet states, providing the first detailed report of ab initio dynamics around a three-state intersection (3SI). There is a significant energy barrier to ESIPT on S1, and further pyramidalization of the twisted structure leads to the minimal energy S1/S0 intersection and energetic terminal point of excited-state dynamics. Kinetics and additional mechanistic details of these pathways are discussed. Significant depletion of the spectroscopic state and recovery of the ground state is seen within the first 250 fs after photoexcitation.
在CASSCF和MRSDCI水平上对激发态势能面（PES）进行表征，随后对丙二醛S2（ππ*）态上的激发态分子内质子转移（ESIPT）进行从头算动力学模拟。质子转移过渡态靠近S2/S1锥形交叉点，导致质子转移与电子弛豫的大量耦合。质子交换在S2上自由进行，但其持续时间受与分子平面扭曲竞争的限制。这种旋转异构体化途径导致三个最低单重态的交叉，提供了围绕三态交叉点（3SI）的从头算动力学的第一份详细报告。在S1上ESIPT存在显著的能垒，扭曲结构的进一步锥形化导致最低能量的S1/S0交叉点和激发态动力学的能量终点。讨论了这些途径的动力学和其他机理细节。在光激发后的前250飞秒内观察到光谱态的显著耗尽和基态的恢复。
