供电子基团修饰对NNI-R系列分子光物理性质的影响

设计了一系列具有不同供电子基团的N-苯基-1,8-萘二甲酰亚胺衍生物(NNI-R), 对它们在二氯甲烷和气相中的几何结构、 电子结构以及室温磷光性能进行了研究. 在二氯甲烷极性溶剂中, NNI-R系列分子的最低单重激发态(S₁)有2个异构体, 分别表现为局域激发(LE)和电荷转移激发(CT). 具有弱给电子体(R=OMe, OH)时的NNI-R分子, 其S₁态为LE结构, 给体和受体间二面角垂直, 其总能量远低于CT结构, 会抑制系间窜越(ISC)的发生, 不会发生磷光现象. 在气相下, NNI-R系列分子的S₁态只有一种稳定的CT结构, 该特征能显著抑制荧光发射, 并有效促进系间窜越, 使NNI-R系列分子的室温磷光发射成为一种可能.

Influences of Electron Donating Groups on the Photophysical Properties of NNI-R Series Molecules †

A series of N-phenyl-1,8-naphthalimide derivatives with different electron donating groups(NNI-R) were designed and studied. The geometric and electronic structures as well as room phosphorescent performance were comparatively studied in dichloromethane solvent and the gas phase. It should be emphasized that in polar solvent(dichloromethane solvent), the NNI-Rs have two isomers of the S₁ state, one has charge-transfer(CT) character, the other has localized excitation(LE) feature. For NNI-R with R=OMe or OH, the total energy of the structure with LE character is far lower than the one of CT structure. which will inhibit intersystem crossing(ISC), and the room temperature phosphorescence will not happen. In the gas phase, all the first singlet excited states of NNI-R have only stable geometry with CT characters, which significantly inhibit the fluorescence(FL) rate and effectively promote the ISC rate. Phosphorescence emission becomes a possibility for NNI-R series molecules at room temperature. As a result, this work likes to contribute to a reliable theoretical basis for the synthesis and characterization of pure organic room temperature phosphorescent materials based on N-phenyl-1,8-naphthalimide.