Monosubstituted Dibenzofulvene-Based Luminogens: Aggregation-Induced Emission Enhancement and Dual-State Emission

The observation of unusual aggregation-induced emission enhancement (AIEE) phenomenon in the deep red wavelength region, dual state emission, and intramolecular charge transfer of dibenzofulvene (DBF) derivatives are described. These consist of a series of newly synthesized donor–acceptor based monosubstituted molecules (DT1, DT2, DP1, and DP2) with their cores comprising DBF molecules. Two luminogens with thiophene-substituted at the ninth position of DBF, viz. DT1 and DT2, displayed AIEE with predominant J-type aggregation due to the effect of intramolecular planarization and formation of nanoparticles in the aggregated state. In the DP1 and DP2 luminogens an extra phenyl ring was inserted at the ninth position of DBFs (between thiophene and DBF) that resulted in a blueshift (∼60 nm) as compared to the DT derivatives and exhibited a unique dual state emission with good quantum yields. This additional phenyl moiety reduces the effective conjugation length toward 2,1,3-benzothiadiazole from DBF and simultaneously interrupts the head to tail interaction and also prevents the J-type aggregation. All the four luminogens exhibited distinctive solvent-dependent photoluminescence (PL) behavior (solvatochromism) because of the efficient intramolecular charge transfer. The DT2 and DP2 luminogens showed heavy atom effect due to the presence of two bromine atoms.