Substituent effects on solid-state emission of 2,7,9-triphenylcarbazoles

Abstract

Previously, we reported polycyclic aromatic hydrocarbons with multiple chromophores exhibit solid-state emission. We report synthesis and photophysical characterization of 2,7,9-triphenyl carbazole derivatives in which the phenyl rings at the 2- and 7-positions are selectively substituted with electron-donating and electron-withdrawing groups. The effects of these substituents on the emission properties were systematically investigated in solution and the solid state. The incorporation of electron-donating groups significantly enhanced the emission properties whereas electron-withdrawing groups had minimal impact. Density functional theory (DFT) calculations revealed that the highest occupied molecular orbitals (HOMOs) are predominantly localized on the carbazole core and electron-rich phenyl rings, while the lowest unoccupied molecular orbitals (LUMOs) are delocalized over the chromophore framework excluding the 9-phenyl moiety. Overall, the present study demonstrates a rational molecular design strategy for enhancing solid-state emission through peripheral electronic tuning of carbazole-based luminophores, with potential implications for the development of efficient organic light-emitting materials.