Minezawa Noriyuki, Kato Shigeki
Department of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan.
J Phys Chem A. 2005 Jun 23;109(24):5445-53. doi: 10.1021/jp0580064.
Intramolecular charge-transfer (ICT) state formation of 4-(N,N-dimethylamino)benzonitrile in acetonitrile solution is studied by the reference interaction site model self-consistent field (RISM-SCF) method. Geometry optimizations are performed for each electronic state in solution with the complete-active-space SCF wave functions. Dynamic electron correlation effects are taken into account by using the multiconfigurational quasidegenerate perturbation theory. Two-dimensional free energy surfaces are constructed as the function of the twisting and wagging angles of the dimethylamino group for the ground and locally excited (LE) states. The calculated absorption and fluorescence energies are in good agreement with experiments. The validity of the twisted ICT (TICT) model is confirmed in explaining the dual fluorescence, and the possibility of the planar ICT model is ruled out. To examine the mechanism of the TICT state formation, a "crossing" seam between the LE and charge-transfer (CT) state surfaces is determined. The inversion of two electronic states occurs at a relatively small twisting angle. The effect of solvent reorganization is also examined. It is concluded that the intramolecular twisting coordinate is more important than the solvent fluctuation for the TICT state formation, because the energy difference between the two states is minimally dependent on the solvent configuration.
采用参考相互作用位点模型自洽场（RISM-SCF）方法研究了4-（N，N-二甲基氨基）苯甲腈在乙腈溶液中的分子内电荷转移（ICT）态形成。使用完全活性空间SCF波函数对溶液中的每个电子态进行几何优化。通过使用多组态准简并微扰理论考虑动态电子相关效应。构建了二维自由能面，作为基态和局域激发（LE）态下二甲基氨基扭转角和摇摆角的函数。计算得到的吸收和荧光能量与实验结果吻合良好。扭曲ICT（TICT）模型在解释双重荧光方面的有效性得到证实，平面ICT模型的可能性被排除。为了研究TICT态形成的机制，确定了LE态和电荷转移（CT）态表面之间的“交叉”缝。两个电子态的反转发生在相对较小的扭转角处。还研究了溶剂重组的影响。得出的结论是，对于TICT态形成，分子内扭转坐标比溶剂涨落更重要，因为两个态之间的能量差对溶剂构型的依赖性最小。
