Meso carbazole linked Bis-BODIPYs: Design, synthesis, structures and properties

In the present study, BODIPY 4 bearing carbazole ring system at meso position was successfully synthesized as a key building block by the acid-catalyzed condensation reaction of 6-bromo-9-ethyl-9H-carbazole-3-carbaldehyde 3 with 2,4-dimethylpyrrole in one step. The Suzuki and Stille coupling synthetic strategies were subsequently applied to the compound 4 for the construction of a new class of bis-BODIPYs 5 and 6 with extended π-conjugation by introducing phenyl and bithiophene as linkers between two N-ethylcarbazole units. The structures of novel compounds 4–6 were identified by mass, 1H and 13C NMR spectroscopy along with single crystal X-ray diffraction techniques. The photo-physical features of the targeted BODIPYs were investigated via absorption and fluorescence spectroscopies in solvents with different polarity. Photophysical studies reveal important transitions between carbazole and BODIPYs in solution state, which could be controlled by solvent polarity. Crystal geometry of the molecules and the optical band gaps were supported by DFT calculations. Electrochemical and in situ spectroelectrochemical properties of the synthesized compounds were also investigated to reveal electropolymerizable properties and electrochromic potentials of the targeted materials. The results suggested that the compounds 5 and 6 can be potentially used as useful materials in a range of electrochemical research areas.