A Descriptor for Accurate Predictions of Host Molecules Enabling Ultralong Room‐Temperature Phosphorescence in Guest Emitters.

Although doping can induce room‐temperature phosphorescence (RTP) in heavy‐atom free organic systems, it is often challenging to match the host and guest components to achieve efficient intersystem crossing for activating RTP. In this work, we developed a simple descriptor ΔE to predict host molecules for matching the guest RTP emitters, based on the intersystem crossing via higher excited states (ISCHES) mechanism. This descriptor successfully predicted five commercially available host components to pair with naphthalimide (NA) and naphtho[2,3‐c]furan‐1,3‐dione (2,3‐NA) emitters with a high accuracy of 83 %. The yielded pairs exhibited bright yellow and green RTP with the quantum efficiency up to 0.4 and lifetime up to 1.67 s, respectively. Using these RTP pairs, we successfully achieved multi‐layer message encryption. The ΔE descriptor could provide an efficient way for developing doping‐induced RTP materials. [ABSTRACT FROM AUTHOR]