One-dimensional π-π stacking induces highly efficient pure organic room-temperature phosphorescence and ternary-emission single-molecule white light

It is extremely challenging to achieve high-efficiency room-temperature phosphorescence (RTP) in pure organic metal-free systems. Herein, we systematically investigated the photophysical properties of thioxanthone (TX) and its halogenated derivatives (TX-R, R = F, Cl, Br, I), and 2-chlorothioxanthone (TX-Cl) exhibits very strong RTP with an absolute quantum yield (phi(RTP)) of 74.7% as a crystal, which is outstanding in pure organic RTP materials. Experimental and theoretical investigations demonstrate that such a high-efficiency RTP of the TX-Cl crystal is attributed to the aggregate emission from one-dimensional strong pi-pi stacking, which significantly enhances both intersystem crossing (ISC, S-1 -> T-n) and phosphorescence radiative rate (T-1 -> S-0). Moreover, a single-molecule white-light emitter (SMWLE) was harvested with the CIE coordinates of (0.31, 0.33) by precisely controlling the doping ratio of TX-Cl in a polymethyl methacrylate (PMMA) film, which consists of ternary emissions: monomer fluorescence, monomer RTP and aggregate RTP. This result provides an important prototype to explore high-efficiency RTP by supramolecular aggregation.