Substituent‐Regulated Photophysical Properties and Self‐Reversible Mechanochromism in Luminescent Pyrrolone Derivatives

Monocyclic compounds with excellent photophysical properties are relatively uncommon compared to fluorophores featuring extensive π-conjugation and polycyclic frameworks. Herein, we describe a series of 2,2-dimethyl-1,2-dihydro-3H-pyrrol-3-ones and a systematic investigation of their photophysical properties. Strategic substitution at N-1, C-4, and C-5 along the periphery of this nonaromatic five-membered N-heterocyclic scaffold endowed it with interesting photophysical properties. Specifically, the C-4/C-5 positions were functionalized with phenyl, anisyl, and styryl moieties, while the N-1 position was modified with alkyl, acetyl, and Boc groups. A combination of steric and electronic effects exerted by these substituents enabled the pyrrolone derivatives to exhibit large Stokes shifts, aggregation- and viscosity-dependent emission, and dual-state emission (DSE) in selected derivatives. Some of these derivatives also exhibited self-reversible mechanochromism, which could be reproduced over multiple cycles.