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.