从CASPT2/CASSCF势能面和单重态/三重态激发态分子动力学模拟揭示硫脲的物理化学
Unveiling the photophysics of thiourea from CASPT2/CASSCF potential energy surfaces and singlet/triplet excited state molecular dynamics simulations
摘要：
本文从激发态和基态势能面的形貌和混合单重态/三重态量子经典分子动力学模拟推断的信息出发，描述了光激发硫脲在气相和溶液中的衰变机制。我们的气相结果揭示了T1/S 0系间交叉作为占主导地位的（49%）的内在衰变通道的基态，达到人口0.28在我们的模拟的最后时间（10 ps）。T1的布居将发生在从光谱S2电子态到S1的内部转换之后，随后是S1->T2系间穿越和T2->T1内部转换过程。还观察到仅沿单重态歧管发生的次要衰变通道，即S2-> S 0（33%）和S1-> S 0（18%），在气相中光激发硫脲的弛豫中起作用。在我们的模拟中明确纳入水-硫脲相互作用被发现挑起一个非常显着的延迟衰减到系统的基态，没有过渡到S 0被注册在我们的模拟的第一个10 ps。分子间的振动能量重新分配和明确的氢键之间建立的相互作用和硫脲的NH 2基团被发现在结构上或能量上阻碍访问的系统间的交叉或内部转换漏斗与基态。
英文摘要：
This work describes the decay mechanism of photoexcited thiourea, both in gas phase and in solution, from the information inferred from the topography of the excited and ground state potential energy surfaces and mixed singlet/triplet quantum classical molecular dynamics simulations. Our gas phase results reveal T1/S0 intersystem crossing as the dominant (49%) intrinsic decay channel to the ground state, which reaches a population of 0.28 at the final time of our simulations (10 ps). Population of the T1, would occur after internal conversion to the S1 from the spectroscopic S2 electronic state, followed by S1->T2 intersystem crossing and T2->T1 internal conversion processes. Minor decay channels occurring exclusively along the singlet manifold, i.e. S2->S0 (33%) and S1->S0 (18%), were also observed to play a role in the relaxation of photoexcited thiourea in the gas phase. The explicit incorporation of water-thiourea interactions in our simulations was found to provoke a very significant delay in the decay to the ground state of the system, with no transitions to the S0 being registered during the first 10 ps of our simulations. Intermolecular vibrational energy redistribution and explicit hydrogen bond interaction established between water molecules and the NH2 group of thiourea were found to structurally or energetically hamper the access to the intersystem crossing or internal conversion funnels with the ground state.
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