Highly Efficient Organic Host/Guest Phosphorescent System with Tunable Lifetime and Color

The tunability of an organic room-temperature phosphorescent (RTP) system is important but rarely reported. In this work, we report a series of host/guest ultralong organic room-temperature phosphorescent materials with lifetime- and color-tuning properties. By doping a nonroom-temperature phosphorescence guest emitter, 1, 8-naphthalimide (NI), into a series of solid host matrices with higher triplet energy levels, the lifetime (0.20–0.81 s) and color (yellow–green) of tunable RTP materials are realized. Phosphorescence quantum yields are up to 19.96%. As the excitation wavelength is switched from 365 to 254 nm, the phosphorescent color changes significantly and the phosphorescent lifetime increases by a factor of almost 2. Notably, the unique dual emission (fluorescence and phosphorescence) of the doped material 4BrBa-NI resulted in a different orange emission. The host/guest doping materials are prepared through cocrystallization or grinding, allowing for efficient energy transfer from the guest to the host. The results indicate that strong intermolecular interactions and the intersystem crossing (ISC) ability of the guest play a significant role. In addition, the security protection and anticounterfeit encryption applications for RTP materials are realized through various methods, such as handwritten pens, screen printing, and dynamic recognition of QR codes, which significantly improve the commercial viability of the RTP materials.