Photoactivation-Enabled Tunable Room-Temperature Phosphorescence and Thermally Activated Delayed Fluorescence in Crystalline Materials.

Photoactivation-enabled tunable room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) are rarely realized in crystalline materials because of their rigid molecular packing. Existing crystalline photoactivated RTP systems generally require pretreatment and have not enabled RTP/TADF regulation. Here, we demonstrate for the first time that intrinsic photoactivated RTP can be achieved in a pretreatment-free crystalline system, while the occurrence of TADF can be switched on or off through rational host-guest engineering. Dinaphtho[2,1-b:1',2'-d]furan (OA) exhibits intrinsic photoactivated RTP at 77 K, when incorporated into three crystalline hosts, forms a general crystalline photoactivated platform at room temperature. Experimental and calculational results indicate that energy level matching and exciton lifetime govern RTP/TADF modulation. Specifically, long-lived excitons in host dibenzofuran (DBF) enable simultaneous RTP and TADF through host-guest energy transfer, whereas methyl 4-(methylamino)benzoate (MAB) and boric acid (BA) as hosts suppress TADF due to mismatched energy levels or rapid exciton quenching. Nevertheless, their RTP emission is facilitated by high crystallinity and rigid hydrogen-bonding networks. Mechanistic analysis indicates that UV irradiation regulates excited-state carrier concentration and transition probability, thereby enabling photoactivation. This work establishes a design strategy for crystalline photoactivated luminescent materials with potential applications for time-dependent anti-counterfeiting.