High quantum yield NIR emission via charge transfer states in buckybowl-TPA based D–A systems

Abstract

The development of highly efficient near-infrared (NIR) emissive materials presents tremendous opportunities across diverse applications, from biological imaging to advanced optoelectronics. While planar aromatic dyes have traditionally dominated this field, we report herein the successful design and synthesis of a novel bowl-shaped NIR dye, TPA-TOS, incorporating the rarely emissive trioxosumanene (TOS) as the acceptor and triphenylamine (TPA) as the donor. In polar solvents, TPA-TOS exhibited weak luminescence confined to the UV region; however, in nonpolar environments, it demonstrated intense NIR emission spanning the 650 to 850 nm range. Remarkably, a quantum yield exceeding 60% in the NIR range was achieved, attributed to an intriguing photo-relaxation pathway. This mechanism involves exciton relaxation from localized excitation to the charge transfer (CT) state, mediated by thermally activated delayed fluorescence (TADF) between CT singlet and triplet states, along with room-temperature phosphorescence (RTP), ultimately transitioning to a long-lived charge-separated (CS) state. The outstanding amphiphilic nature, high quantum yield of NIR dual emission enabled by TADF and RTP, and the generation of a long-lived CS state are likely driven by the pronounced spin–orbit coupling facilitated by the curved sumanene skeleton. This work establishes TPA-TOS as a platform for NIR materials and insights into non-planar photophysics.