2,1,3-Benzoxadiazole and 2,1,3-benzothiadiazole-based fluorescent compounds: Synthesis, characterization and photophysical/electrochemical properties

Six new fluorescent compounds derived from 2,1,3-benzoxadiazole and 2,1,3-benzothiadiazole heterocycles with varying numbers of alkoxy chains were successfully synthesized. Sonogashira cross-coupling was used as the key synthetic step to link the central and terminal aromatic units through an acetylenic linker unit which ensures molecular planarity and extension of the conjugation. All of the synthesized compounds showed UV–vis absorption in the 426–437 nm range with reasonably high molar extinction coefficients. All six compounds emit in the green region of the visible spectrum with reasonably large Stokes shifts (95–107 nm) and medium emission efficiencies (Φf = 0.27–0.32). Electrochemical studies showed that the compounds have closely spaced HOMO and LUMO energy levels and that they may present good electron transporting properties.

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► Six new fluorescent compounds based on 2,1,3-benzothiadiazole and 2,1,3-benzoxadiazole cores were successfully synthesized.
► Sonogashira cross-coupling was used as the key synthetic step.
► All the compounds emit in the green region of the visible spectrum with reasonably large Stokes shifts.
► Electrochemical measurements revealed that the target compounds possess small band gaps between 1.91 and 2.57 eV.