Modulation of photophysical properties in o-carborane derivatives and their application in white organic light-emitting diode devices

Abstract

Two derivatives of o-carborane (o-Cb) were synthesized, enabling effective modulation of their photophysical properties by varying the substituents on the carbon atom within the o-Cb cage. CAPCb incorporates phenyl groups into the carbazole–anthracene motif, demonstrating weak dual emissions in solution due to efficient charge transfer (CT) from the carbazole to the o-Cb groups. In contrast, its methyl analog (CAMCb) primarily emits from a locally excited (LE) state in solution. The most notable characteristics were revealed in their solid-state photochemistry. CAMCb displayed multiple photoemissions in the film state, featuring strong LE emission at 450 nm and slightly weaker CT emission at 640 nm. In comparison, CAPCb exhibited weaker LE emission at 430 nm and stronger CT emission at 620 nm. This indicates that the CT states can be selectively activated or deactivated based on the substituents on the o-Cb and the phase. Minor modifications in molecular geometries through changes in the substituents at the o-Cb cage significantly influence their excited-state properties and emission characteristics. The distinct properties of CAPCb and CAMCb were utilized in the fabrication of white OLED devices, which demonstrated cool white emission with Commission Internationale de L’Eclairage (CIE) coordinates of (0.37, 0.30) and a correlated color temperature (CCT) of 3556 K measured at 500 cd m⁻².