Study on the Electronic Structure of the Excited States and its Reaction of Triple Bond Conjugated Molecules

以下是本研究取得的主要结果。(1)二苯基多炔（DPY）在T_1态具有线性平面结构，属于D_<2h>点群，其特征归属为^3B_<1u>（π_xπ_x^*）。(2)DPY的T_1（π_xπ_x^*）态具有非常大的负D值，且D值随分子尺寸的增大而增大. (3)用T_1（^3π_xπ_x^*）态和上层^3 Au（π_xπ_y^*）态之间的自旋轨道相互作用解释了大的负D值。(4)这两个状态之间的能隙由所观察到的D值和自旋轨道矩阵的计算确定，表明该值随着三键数目的增加而减小。(5)在从T_1态到S_0态的衰变过程中也发现了快速的无辐射跃迁。k<nr>值随T_1和S_0态之间能量分离的减小而增大，表明它们之间的Franck-Condon因子对非辐射失活的重要性。(6)DPY<1g>磷光光谱中出现的由B_b电子振动带引起的伴带表明，由于<1g>环扭转运动促进了T_1（π_xπ_x^*）和^3π_xπ_y电子振动耦合，T_1态的势能面沿着B_b坐标变浅. (7)因此，DPY中T_1（^3B_<1u>：π_xπ_y^*）和Tu（^3Au：π_xπ_y^*）态之间的能量接近不仅通过自旋-轨道相互作用增加了π参数的负D值，而且通过电子振动相互作用加速了T_1态的无辐射衰变.

The following are the main results obtained in the present study.(1) Diphenylpolyynes (DPY) have a linear planar structure belonging to the D_<2h> point group in the T_1 states, which were assigned to ^3B_<1u> (π_xπ_x^*) in character.(2) The T_1 (π_xπ_x^*) states of DPY have unusually large negative D values for the ZFS parameters that increase with increasing the molecular size.(3) The large negative D value was interpreted in terms of the spin-orbit interaction between the T_1(^3π_xπ_x^*) state and the upper-lying ^3Au (π_xπ_y^*) state.(4) The energy gap between these two states was determined from the observed D values and the calculation of the spin-orbit matrix, indicating that the value decreases with increasing the number of triple bonds.(5) The rapid radiationless transition was also found in the decay from the T_1 state to the S_0 state. The k_<nr> value increases with the decrease in the energy separation between the T_1 and S_0 states, indicating the importance of the Franck-Condon factor between them for the nonradiative deactivation.(6) The appearance of the satellites due to the b_<1g> vibronic bands in the phosphorescence spectra of DPY suggests that the potential surface in the T_1 states would be shallow along the b_<1g> coordinate by the vibronic coupling between the T_1 (π_xπ_x^*) and the ^3π_xπ_y states promoted by the ring twisting motion.(7) Therefore, it is concluded that the energy proximity between the T_1 (^3B_<1u>:π_xπ_y^*) and Tu(^3Au:π_xπ_y^*) states in DPY not only increases the negative D values of the ZFS parameters by the spin-orbit interaction but also accelerates the nonradiative decay from the T_1 state by the vibronic interaction.