Dual-State Emission and Two-Photon Absorption Tuned by Benzonitrile Substitution in 2,3,4,5-Tetraphenyl-1H-Pyrrole

A series of nine 2,3,4,5-tetraphenyl pyrrole derivatives presenting benzonitrile substitution at different positions was designed and synthesized for this work. Their structure–emission property relationships were investigated in depth through a joint advanced experimental and computational effort. Our ultrafast and non-linear spectroscopic results showed more efficient intramolecular charge transfer and enhanced two-photon absorption cross sections when the benzonitrile substitution is at position 3 of the central pyrrole. On the other hand, an intriguing dual-state emission behaviour was found to be activated by substitution at position 2, with exceptionally large photoluminescence quantum yields exhibited both in solution and in the solid state. Indeed, the quantum chemical simulations revealed for the derivatives functionalized at position 2 that the distorted geometry of the benzonitrile substituent with respect to the phenyl ring prevents emission quenching in the aggregate species by π-π stacking interactions. Our findings shed new light on optimized design strategies of highly emitting materials for efficient optoelectronic devices.