Near-infrared TADF-type organic afterglow materials

Abstract

Because of the energy gap law, as well as the spin-forbidden nature of triplet formation and transformation, it remains formidable task to achieve efficient and long-lived organic afterglow materials with long emission wavelengths, especially in the near-infrared region, under ambient conditions. Here we incorporate TADF-type afterglow mechanism in dopant-matrix systems which features a moderate k_RISC of 10¹-10² s⁻¹ to harvest triplet energies, boost afterglow efficiency and maintain afterglow lifetime. Specifically, we design a series of boron difluoride curcuminoid (CurBF₂) compounds to serve as luminescent dopants. Organic matrices of crystalline nature and with carbonyl groups are selected to suppress triplet quenching by their rigid microenvironment and populate triplet states via dipole effect developed in our group. The resultant dopant-matrix systems display near-infrared TADF-type organic afterglow with emission wavelength >700 nm, quantum yield around 10 % and afterglow lifetime >10 ms, which can function as deep-penetrating and background-independent bioimaging probes.