Triple-triarylboron-functionalized phenothiazine as a thermally stable dual-function material for enhanced luminescence and fluoride detection

Abstract A triarylboron-functionalized phenothiazine derivative, 3,7,10-tris(4-(dimesitylboryl)phenyl)-10H-phenothiazine (3B-PTZ), was synthesized by covalent integration of 3 electron-deficient triarylboron units onto a phenothiazine (PTZ) electron-donor core. Comparative analysis with its mono-boron analog (B-PTZ) revealed that multi-boron functionalization significantly changed the photophysical properties and enhanced the thermal stability. The introduction of more boron acceptors stabilizes both the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of 3B-PTZ relative to B-PTZ, with a greater stabilization of the HOMO that results in a slightly wider bandgap. 3B-PTZ exhibits intense intramolecular charge-transfer absorption (400 to 520 nm) and solvent-dependent emission with attenuated solvatochromism (Δλem = 37 nm) relative to B-PTZ (Δλem = 129 nm), attributed to the higher symmetry of 3B-PTZ demonstrating high fluorescence quantum efficiency (ΦF = 65.3% in toluene) and exceptional thermal stability (Td = 436 oC, Tm = 407 oC). Its fluoride-responsive behavior features ratiometric absorption shifts and fluorescence quenching via B–F bond formation, enabling sensitive F− detection. These properties position 3B-PTZ as a dual-functional material for electroluminescent devices and fluoride-ion probes.