Mechano-induced photoluminescence colour change in tetraphenylethylene -based aza-N,O-chelated boron difluoride complexes

Two new asymmetric aza-N,O-chelated organoboron complexes DMFPT ((E)-5-(4-(dimethylamino)phenyl)-2,2-difluoro-3-(4-(1,2,2-triphenylvinyl)benzylidene)-2,3-dihydro-1,3,4,2-oxadiazaborol-3-ium-2-uide) and DFPT ((E)-2,2-difluoro-5-phenyl-3-(4-(1,2,2-triphenylvinyl)benzylidene)-2,3-dihydro-1,3,4,2-oxadiazaborol-3-ium-2-uide) have been designed and synthesized. The incorporation of a dimethylamino donor unit into organoboron complexes resulted in a more pronounced AIE and mechanofluorochromic response. PXRD (powder X-ray diffraction), DSC (differential scanning calorimetry) and spectral data indicated that the reversible mechanofluorochromic behavior of the two asymmetric organoboron compounds was attributed to the crystalline-amorphous phase transition. The planarization of the molecular conformation and subsequent PICT (planar intramolecular charge transfer) resulted in the red-shift of fluorescence spectra upon grinding. The newly emerged organoborons may be the candidates for potential applications in sensing, and optical data storage fields, and so on. We expect the obtained results would be helpful to promote the future design and applications of more advanced aza-N,O-chelated organoboron based dyes.