Pyridyl substitution control dynamics and shape dependence of fluorescent aggregates

The presence and the position of the heteroatom strongly influence the aggregation. [Display omitted] •The position of pyridyl nitrogen impacts significantly the aggregation process.•Depending on the position the luminescence of the aggregates changes.•Molecular dynamics simulation aids to understand the molecular interactions.•van der Waal’s forces and weak hydrogen bonding are responsible for aggregation.•Simulation confirms the significance of the position in the aggregation process. Nitrogen substitution on 2-(2′-hydroxyphenyl)benzimidazole (HPBI) showed impressive changes in photophysical properties. Hence, in this work, we investigated the effect of pyridyl substitution on HPBI on the kinetics and the shape of the aggregates. It was found that the presence and the position of the heteroatom strongly influence the aggregation. 2-(2'-Hydroxyphenyl)-3H-imidazo[4,5-c]pyridine (HPIP-c) forms small rods and 2-(2'-hydroxyphenyl)-3H-imidazo[4,5-b]pyridine (HPIP-b) produces long needle like structures. The normal emissions of both the molecules were also enhanced along with tautomer emission. In addition, molecular dynamics simulations were performed to monitor the aggregation process. The aggregation was elucidated in term of electrostatic interaction, van der Waals interaction and hydrogen bonding.