Multi-Stimuli Responsive Luminescent Dye Materials

Emissive β-diketones (bdks) and difluoroboron β-diketonate complexes (BF2bdks) exhibit multi-stimuli responsive luminescent properties in solution, suspended aggregates and other solid states. These properties include solvatochromism, viscochromism, aggregation-induced emission (AIE), thermal and mechanochromic luminescence (ML), halochromism and pH sensing. Azepane-substituted bdk ligands and boron coordinated dyes showed responsive emission changes in color or intensity after applying different external stimuli. By restricting the intramolecular C−C bond rotation, the azepane compounds displayed an enhanced emission in solution with a dramatic quantum yield increase. Substituent ring size and heterocyclic substitution effects on various optical properties were investigated by substituting the bdk ligands and boron dyes with four to seven membered amine rings and six-membered heterocycles (i.e., piperidine, morpholine and 1-methyl piperazine). In lipid model studies, liquid-ordered (Lo) and liquid-disordered (Ld) phase separation and viscosity mapping were accomplished with a series of dimethylamino-substituted BF2bdk dyes in giant unilamellar vesicles (GUVs). Structure-property relationships of the bdk and BF2bdk compounds were also studied by changing electron donor/acceptor groups and conjugation length. Given the multiple stimuli-responsive luminescent properties, the bdk ligands and boron complexes show great promise in sensing and imaging applications.