Piezochromic luminescence of AIE-active triphenylamine-based aza-N,O-chelated boron difluoride complexes

Two new AIE-active triphenylamine-based aza-N,O-chelated boron difluoride dyes (E)-3-(4-(diphenylamino)benzylidene)-2,2-difluoro-5-phenyl-2,3-dihydro-1,3,4,2-oxadiazaborol-3-ium-2-uide (TPA-H) and (E)-5-(4-chlorophenyl)-3-(4-(diphenylamino)benzylidene)-2,2-difluoro-2,3-dihydro-1,3,4,2-oxadiazaborol-3-ium-2-uide (TPA-Cl) were designed and synthesized. The reversible mechanochromism and piezochromism for TPA-H and TPA-Cl under mechanical stimulus and hydrostatic pressure were observed, while TPA-Cl with a chlorine atom gave a more sensitive and pronounced mechanochromic and piezochromic response under mechanical stimulus and hydrostatic pressure. Powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), the field emission scanning electron microscopy (FESEM), high-pressure PL and UV–vis absorption spectra analysis were applied to further investigated their different mechanochromism and piezochromism. Fine-tuning the molecular structures of triphenylamine-based aza-N,O-chelated boron difluoride dyes allowed convenient modulation of their optical properties and mechanoresponsive behaviors.