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Abstract：
We provide a method to regulate intramolecular charge transfer (ICT) through distorting fragment dipole moments based on molecular planarity and intuitively investigate the physical mechanisms of one-photon absorption (OPA), two-photon absorption (TPA), and electron circular dichroism (ECD) properties of the multichain 1,3,5 triazine derivatives o-Br-TRZ, m-Br-TRZ, and p-Br-TRZ containing three bromobiphenyl units. As the position of the C-Br bond on the branch chain becomes farther away, the molecular planarity is weakened, with the position of charge transfer (CT) on the branch chain of bromobiphenyl changing. The excitation energy of the excited states decreases, which leads to the redshift of the OPA spectrum of 1,3,5-triazine derivatives. The decrease in molecular plane results in a change in the magnitude and direction of the molecular dipole moment on the bromobiphenyl branch chain, which weakens the intramolecular electrostatic interaction of bromobiphenyl branch chain 1,3,5-triazine derivatives and weakens the charge transfer excitation of the second step transition in TPA, leading to an increase in the enhanced absorption cross-section. Furthermore, molecular planarity can also induce and regulate chiral optical activity through changing the direction of the transition magnetic dipole moment. Our visualization method helps to reveal the physical mechanism of TPA cross-sections generated via third-order nonlinear optical materials in photoinduced CT, which is of great significance for the design of large TPA molecules.
摘要：
我们提供了一种基于分子平面性通过扭曲碎片偶极矩来调节分子内电荷转移（ICT）的方法，并直观地研究了单光子吸收（OPA）的物理机制，双光子吸收(TPA),多链1，3，5三嗪衍生物o-Br-TRZ的电子圆二色性（ECD）性质，m-Br-TRZ,和含有三个溴联苯单元的对-Br-TRZ。随着支链上C-Br键的位置变得更远，分子平面性被削弱，随着溴代二苯支链上电荷转移(CT)位置的变化。激发态的激发能量减小，这导致1,3,5-三嗪衍生物的OPA谱的红移。分子平面的减少导致溴代二苯支链上分子偶极矩的大小和方向发生变化，这削弱了溴联苯支链1,3,5-三嗪衍生物的分子内静电相互作用，并削弱了TPA中第二步跃迁的电荷转移激发，导致增加的吸收截面。此外，分子平面性还可以通过改变跃迁磁偶极矩的方向来诱导和调节手性光学活性。我们的可视化方法有助于揭示光致CT中通过三阶非线性光学材料产生的TPA横截面的物理机制，这对于大TPA分子的设计具有重要意义。
