Two Facile Isoindoline‐1‐One‐Based Difluoroboron Compounds: Aggregation‐Induced Emission, Mechanofluorochromism, and Their Practical Application

To further investigate the optical properties of pyridyl-isoindoline-1-one derivatives and expand their practical applications, two novel difluoroboron dyes, a pyrenyl-substituted compound Isoin-py BF₂ and an anthryl-substituted compound Isoin-en BF₂, were conveniently synthesized in three steps. Both compounds exhibited aggregation-induced emission in DMSO/water mixtures and solid-state luminescence. Furthermore, their solutions could be used as developers for latent fingerprint imaging on three types of substrates. Interestingly, the imaging mechanism originates from a specific response of Isoin-py BF₂ to oleic acid and of Isoin-en BF₂ to lactic acid, both secreted in sweat. The developer based on Isoin-en BF₂ could clearly reveal all three levels of fingerprint features, outperforming Isoin-py BF₂ in detail resolution. Additionally, Isoin-py BF₂ exhibited reversible mechanofluorochromic behavior due to a phase transition between crystalline states, enabling its application ink-free writing. In contrast, Isoin-en BF₂ showed no mechanofluorochromism due to its strong crystallinity. This work provides a reference for the molecular design and development of boron-pyridyl-isoindoline-1-one-based dyes containing bulky π-conjugated substituents.