Amatatsu Yoshiaki
Faculty of Engineering and Resource Science, Akita University, Tegata Gakuen-cho, Akita 010-8502, Japan.
J Phys Chem A. 2005 Aug 18;109(32):7225-35. doi: 10.1021/jp051083e.
Ab initio calculations have been performed to examine the photochemical behavior of 4-(dimethylamino)benzenzonitrile (DMABN). The conical intersection between S2 and S1 (S2/S1-CIX), where the internal conversion takes place after the main transition of S0-S2 at the equilibrium geometry in S0, is characterized by a dimethylamino-twisted quinoid structure where aromaticity of the benzene ring is lost. The optimized geometry of the charge transfer (CT) state in S1 has a feature similar to that of S2/S1-CIX but is not energetically stabilized so much. Consequently, electronically excited DMABN with CT character relaxes into the most stable locally excited (LE) state in S1 through a recrossing at S2/S1-CIX in gas phase or nonpolar solvent. In polar solvent, in contrast, the equilibration between LE and CT takes place in S1 so that the CT state is more stable because of electrostatic interaction. The excited states of DMABN derivatives have been also examined. On the basis of the present computational results, a new and simple guiding principle of the emission properties is proposed, where conventional twisted intramolecular CT (TICT) and planar intramolecular CT (PICT) models are properly incorporated.
已进行从头算计算以研究4-(二甲基氨基)苯甲腈(DMABN)的光化学行为。S2和S1之间的锥形交叉点(S2/S1-CIX)，即在S0平衡几何结构下S0-S2的主要跃迁后发生内转换的位置，其特征是二甲基氨基扭曲的醌型结构，其中苯环的芳香性丧失。S1中电荷转移(CT)态的优化几何结构具有与S2/S1-CIX相似的特征，但在能量上没有得到很大程度的稳定。因此，具有CT特征的电子激发DMABN在气相或非极性溶剂中通过在S2/S1-CIX处的重新交叉弛豫到S1中最稳定的局域激发(LE)态。相比之下，在极性溶剂中，LE和CT之间的平衡在S1中发生，因此由于静电相互作用，CT态更稳定。还研究了DMABN衍生物的激发态。基于目前的计算结果，提出了一种新的、简单的发射性质指导原则，其中传统的扭曲分子内电荷转移(TICT)和平面分子内电荷转移(PICT)模型被适当纳入。
