Aggregation induced emission in one easy step: pyridinium AIEgens and counter ion effect.

Protonation of pyridines with a strong acid is a general and straightforward approach to achieve efficient aggregation induced emission (AIE) in structurally remarkably simple organic molecules that lack any of the conventional luminophores. The relationship between the nature of counter ion and the AIE efficiency is demonstrated. The superiority of the perchlorate counter ion is attributed to efficient stabilization of the key intermolecular π + -π interactions between neighboring luminophore molecules in the crystal lattice.