Photoinduced Ion Pair Generator Based on Triangle Terarylene

Abstract Photoresponsive systems capable of generating ion pairs provide promising opportunities for light-controlled catalysts, yet the structural factors governing ion-pair formation and stability remain poorly understood. Here we report a series of terarylene derivatives (1o–3o) that undergo photoinduced cyclization to generate ion pairs with distinct reactivity profiles. Spectroscopic studies combined with density functional theory calculations reveal that ion-pair formation strongly depends on the leaving group and solvent polarity. While 1o readily generates a highly stable cationic species upon irradiation even in nonpolar media, 2o and 3o exhibit alternative pathways involving neutral closed intermediates or other photoinduced processes. These differences give rise to markedly different photochemical behaviors in polar and nonpolar media. Notably, the photoinduced ion pairs exhibit catalytic activity in ring-opening polymerization reactions. Whereas 1o promotes self-initiated cationic polymerization, 2o and 3o require external protic initiators under the conditions examined, while the specific catalytic role of the counteranion was assumed as a working hypothesis. These findings provide structure–reactivity insights for controlling photoinduced ion-pair formation and demonstrate their potential as light-activated catalysts.