Study of two benzophenone-based difluoroboron compounds containing triphenylamine units: mechanofluorochromic behavior and latent fingerprint imaging

Abstract

To further explore the mechanofluorochromic properties of benzophenone derivatives and their potential applications, two asymmetric benzophenone-based difluoroboron compounds (TPA-BP-BF₂-1 and TPA-BP-BF₂-2) were designed and synthesized. It was found that the emission spectrum of the solid powder was red-shifted from 520 nm to 562 nm under the stimulation of mechanical force for compound TPA-BP-BF₂-2 with a 3,5-di-tert-butyl salicylaldehyde moiety. Its luminescent color underwent a conspicuous change, and its mechanofluorochromic behavior was reversible after fumigation, which was caused by a phase transition between the crystalline and amorphous states. However, compound TPA-BP-BF₂-1 with a 3-tert-butyl salicylaldehyde section did not exhibit MFC behavior due to its amorphous stacking mode and a smaller difference value of the dipole moment between the ground and excited states. The two compounds could be used as developers to detect latent fingerprints on the surface of glass, based on their aggregation-induced emission performance in THF/water mixture. Additionally, compound TPA-BP-BF₂-2 could be fabricated as a simple LED paint-coating according to its reversible mechanofluorochromic behavior. This work provides a reference for exploring the potential applications of benzophenone derivatives.