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.