Design and Photophysical Investigation of Schiff Base-Functionalized Pyrrolo[3,2-c]carbazoles

Two pyrrolo[3,2-c]carbazole-based Schiff bases 5a and 5b were synthesized via condensation of pyrrolo[3,2-c]carbazole-2-carbohydrazide with benzaldehyde and p-bromobenzaldehyde. Their structures were confirmed by NMR, FT-IR, MALDI-TOF, and X-ray crystallography. UV-Vis spectra of the compounds showed bands at 300-380 nm, corresponding to π→π* and n→π* transitions, were showed minimal effects by solvent or concentration. Fluorescence studies revealed dual emission behavior, indicating the coexistence of multiple emissive states in the excited state, particularly in polar solvents. The fluorescence quantum yields of 5a and 5b were determined as 0.44 and 0.47, respectively. These results highlight the structural and photophysical versatility of pyrrolo[3,2-c]carbazole Schiff bases and demonstrate their potential for applications in fluorescent sensing and optoelectronic materials.