Institut für Physikalische Chemie, Friedrich-Schiller-Universität Jena, Helmholtzweg 4, 07743 Jena, Germany.
J Phys Chem A. 2010 Sep 2;114(34):9342-8. doi: 10.1021/jp104898t.
The ground state potential energy surface of the model molecular rotor 2-cyclopentylidene-tetrahydrofuran (CPTHF) has been characterized by calculating minimum energy conformations, racemization pathways, and rotational barriers with high level ab initio electronic structure calculations. Two conformers with their corresponding enantiomers are found. The activation barriers for racemization are negligible, therefore thermal racemization takes place at room temperature. Torsional transition states, calculated using multiconfigurational CASSCF calculations, show twisted and pyramidalized biradical structures. Additionally, the photochemistry of CPTHF has been investigated using the accurate MS-CASPT2/CASSCF methodology. In the UV spectrum it is found that the spectroscopic state is the S(1), which corresponds to a pipi* transition within the ethylene moiety. To understand light-triggered isomerization around the C=C bond, five conical intersections between the S(0) and S(1) have been located for each conformer of CPTHF, which allow the system to rapidly decay to the electronic ground state.
采用高精度从头算电子结构计算方法，对模型分子转子 2-环戊基四氢呋喃（CPTHF）的基态位能面进行了研究，计算了最低能量构象、外消旋途径和旋转势垒。发现了两种具有对应对映异构体的构象。外消旋化的活化势垒可以忽略不计，因此在室温下会发生热消旋化。使用多组态 CASSCF 计算得到的扭转过渡态呈现扭曲和三角锥形双自由基结构。此外，还采用精确的 MS-CASPT2/CASSCF 方法研究了 CPTHF 的光化学。在紫外光谱中发现，光谱态是 S(1)，这对应于乙烯部分的 pipi*跃迁。为了理解 C=C 键周围光触发的异构化，在 CPTHF 的每个构象中，都定位了 S(0)和 S(1)之间的五个锥形交叉点，这使得系统能够迅速衰减到电子基态。
