AIE Active Carbazole-Benzothiazole Based ESIPT Motifs: Positional Isomers Directing the Optical and Electronic Properties

Three positional isomers based on carbazole (Cz) and hydroxy benzothiazole (HBT) were synthesized targeting solid state organic emitters by Suzuki coupling reaction and their optical, structural and electronic properties were compared. The changing of position of HBT unit on 9-phenyl-9H-carbazole alters the optical and structural properties significantly. The synthesized compounds are highly emissive in solid and aggregated state (Φ_f=∼ 40 %) and weakly emissive in solvents of different polarities (Φ_f=2.6-17 %). The difference in the fluorescence quantum efficiency among the positional isomers can be assigned to conformational differences which were further supported by geometrical parameters computed by DFT computations. The present Cz-HBT based ESIPT motifs are endowed with aggregation induced emission (AIE), solid state and polarity sensitive emission with large Stokes shift.