A host-guest organic afterglow system with significant guest induced enhancement of phosphorescence

In this article, an effective host-guest system with intense afterglow and stimuli-responsive properties is described. Br-BID-Py (host) crystals emit weak phosphorescence and NMe2-BID-Py (guest) crystals are not phosphorescent. However, when NMe2-BID-Py is doped into the Br-BID-Py crystals, the afterglow of the host is enhanced. The afterglow exhibits a unique thermally activated property, which is due to the effective intersystem crossing from the guest to the host via energy transfer. Br-BID-Py (host) and NMe2-BID-Py (guest) show small structural differences, which facilitate energy transfer with each other in the crystal state. The energy transfer process is evidenced by excitation photoluminescence spectra and UV–vis absorption spectra. To date, the host-guest afterglow organic system where the guest enhances the intrinsic afterglow of the host is rarely reported. Moreover, both Br-BID-Py and NMe2-BID-Py display stimuli-responsive properties because of protonation of pyridine, which is inherited by the hybrid host-guest crystals. The host-guest crystals demonstrate rare proton-induced afterglow shift observed by direct visualization by eye. Finally, the application of the host-guest afterglow material and its stimulus-responsive property in information encryption is displayed. To our best knowledge, this example is a rare stimulus-responsive organic afterglow material fabricated via the strategy of a host-guest doping system.