Understanding Polymorphism-Dependent Emission Properties of Molecular Crystals with a Refined QM/MM Approach
作者单位：School of Chemistry and Chemical EngineeringKey Laboratory of Mesoscopic Chemistry of Ministry of EducationInstitute of Theoretical and Computational ChemistryNanjing University State Key Laboratory of Supramolecular Structure and MaterialsCollege of ChemistryJilin University
会议名称：《第十三届全国量子化学会议》
会议日期：2017年
关 键 词：Organic polymorphs emission energies time-dependent density functional theory quantum mechanics/molecular mechanics method generalized energy-based fragmentation method
摘 要：An efficient quantum mechanical/molecular mechanics（QM/MM） approach is developed for investigating polymorphism-dependent emission properties of molecular crystals. In this approach, we proposed a simple and effective way of automatically building cluster models（as the QM region） for the general QM/MM approach to deal with the excited states of molecular crystals. This approach is then applied to understand the polymorphism-dependent emission properties of two organic crystals comprised of 3（5）-（9-anthryl）pyrazole and its isomeride. Our results demonstrated that a monomer model for QM/MM calculations is suitable for describing the emission spectra of the crystal without the π…π stacking *** for the crystal with the notable intermolecular π…π stacking interaction, the most stable trimer model（or at least the most stable dimer model） should be used for accurately describing the corresponding emission spectra. The effect of the π…πstacking interaction on the emission properties of crystals can be understood by the fact that the intermolecular π…π interactions can significantly reduce the energy gap between frontier molecular orbitals of molecular clusters（dimers or trimers）. The results from the present work provide useful guidelines for understanding and designing the luminescent materials.