Aggregation-Induced Emission of Bis(imino)acenaphthene Zinc Complexes: Photophysical Tuning via Methylation of the Flanking Aryl Substituents

Bis­(imino)­acenaphthene zinc complexes with methylated aryl substituents have been examined from the standpoint of their photoluminescent properties. Although complexes 1–4 proved to be nonemissive in solution, complexes 1 and 2 were found to emit via an aggregation-induced emission pathway. On the other hand, complexes 3 and 4 were found to be nonemissive in the solid state. Detailed crystallographic studies of complexes 1–4 provided valuable insights into the structural differences between the emissive (1 and 2) and nonemissive complexes (3 and 4), particularly with respect to their molecular structures and crystal-packing environments. TD-DFT theoretical calculations were carried out and were found to support the hypothesis that the phosphorescent emissions of 1 and 2 are due to the existence of intermolecular π-stacking interactions within the crystal lattices. Finally, a series of solvatomorphs of complexes 1 and 2 were synthesized and their emissive properties were studied.