Effect of para-aryl-substituted N-phenyl groups on the photophysical properties of highly fluorescent dibenzo[c,g]carbazole-based chromophores

Abstract

Dibenzo[c,g]carbazole (DBC) derivatives are an emerging class of fused-ring carbazole chromophores that exhibit promising optoelectronic properties. However, challenges with their synthesis mean that their photophysical properties remain poorly understood. In this study, we successfully synthesized a series of DBC-based chromophores bearing para-aryl-substituted N-phenyl groups (Ar = phenyl, naphthyl, anthracenyl, pyrenyl, and carbazolyl). We then elucidated the structure–property relationships that govern their photophysical behavior. The DBC core scaffold was established through the Cu(II)-catalyzed oxidative tandem coupling and cyclization of 2-naphthylamine, followed by Suzuki or Buchwald–Hartwig coupling to introduce extended aromatic substituents. All compounds exhibited strong absorption in the 305–367 nm range and intense emission with high photoluminescence quantum yields (Φ_PL = 74–97% in solution and 67–74% in film). Theoretical calculations revealed that a moderately twisted geometry between the DBC moiety and para-aryl-substituted N-phenyl unit allowed for locally excited π–π* transitions with partial intramolecular charge transfer, resulting in red-shifted emission. The impressive emission efficiencies and thermal stabilities of these DBC-based chromophores make them promising candidates for high-performance optoelectronic materials.