Theoretical study on aggregation-induced emission of new multi-layer 3D chiral molecules

Multilayer three-dimensional (3D) chiral molecules have potential application in luminescent material fields, but the mechanism of their AIE effect is not clear. In this work, the theoretical mechanism of the aggregation-induced emission (AIE) effect has been studied for three 3D molecules of 2-X-1,3-bis(8-(4-Y-phenyl)naphthalen-1-yl)-1,3-dihydrobenzo[d][1,3,2] diazapho-sphole-2-oxie (A. X = NH2, Y = H; B. X = i-Pr, Y = H; C. X = NH2, Y = OMe). The geometrical structures and spectral properties in solution, crystal and aggregation are discussed using the combined approach of molecular dynamics (MD), DFT/TD-DFT and ONIOM QM/MM calculations. The S-0 and S-1 structural changes of 3D molecules show that the variation of the naphthalene and benzene rings is reduced in aggregation. Huang-Rhys (HR) factor and reorganisation energy are smaller in aggregation than in solution, especially in low-frequency vibration modes. It suggests that aggregation restricts the rotation of benzene and naphthalene rings and constrains the low-frequency vibration modes, which allows the radiated channel of the excited state molecule to be opened and glow when aggregated. This study provides an excellent explanation for the AIE phenomenon of 3D chiral molecules in experiments.