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.