Photophysical properties of some novel tetraphenylimidazole derived BODIPY based fluorescent molecular rotors
Strategic designing, synthesis and thorough characterizations of four novel hydroxyl-substituted tetraphenylimidazole (HPI) based boron dipyrromethene (BODIPY) fluorophores (HPIB1HPIB4) have been reported. Single crystal X-ray structure determination unveiled non-planar twisted orientation for these molecules. The non-planar orientations entirely restrict detrimental interactions and avoid non-radiative relaxation pathway for excited state in solid/aggregated state and make them AIE active. AIE characteristics for these compounds have been related to fine J-aggregations (evident from crystal structures) along with restricted intra-molecular rotations (RIR). These display significant sensitivity toward viscosity and can serve as fluorescence molecular rotors due to multiple phenyl groups around imidazole ring, which has been affirmed by measuring fluorescence quantum yield and lifetime.