Tunable Aggregation-Induced Emission to Aggregation-Caused Quenching Transition in Benzimidazole-Acrylonitrile Luminogens: Experimental and Theoretical Insights

Abstract

Benzimidazole–acrylonitrile conjugates represent a promising yet underexplored class of luminogens for solid-state emission and functional optoelectronic applications. In this work, four such conjugates (1–4) were synthesized via L-proline-catalyzed Knoevenagel condensation of 2-(1H-benzo[d]imidazol-2-yl)acetonitrile with diverse aldehydes. Their photophysical behaviors were systematically examined, highlighting aggregation-induced emission (AIE) and aggregation-caused quenching (ACQ) effects. Compounds 1 and 2 exhibited AIE characteristics in THF–water mixtures due to restricted intramolecular motions, while brominated derivatives 3 and 4 showed ACQ behavior attributed to heavy-atom-modulated nonradiative decay. SEM analyses revealed distinct self-assembled morphologies, while DLS measurements confirmed the formation of nanoparticles. PXRD diffraction patterns conforms the crystalline nature of the compounds. Complementary DFT and TD-DFT calculations provided insights into the electronic structures and charge-transfer characteristics, in good agreement with experimental observations. Overall, these results identify benzimidazole–acrylonitrile scaffolds as efficient solid-state emitters with strong potential for optoelectronic and sensing applications.