Room-Temperature Phosphorescence in Pure Organic Materials: Halogen Bonding Switching Effects

Organic room-temperature phosphorescence (ORTP), when combined with external stimuli-responsive capability, is very attractive for sensors and bio-imaging devices, but remains challenging. Herein, by doping two beta-iminoenamine-BF2 derivatives (S-2CN and S-2I) into a 4-iodoaniline (I-Ph-NH2) crystalline matrix, the formation of S-2CN center dot center dot center dot I-Ph-NH2 and S-2I center dot center dot center dot I-Ph-NH2 halogen bonds leads to bright-red RTP emissions from these two host-guest doped crystals (hgDCs) with quantum efficiencies up to 13.43% and 15.96 %, respectively. Upon treatment with HCl, the competition of I-Ph-NH2 center dot HCl formation against S-2I center dot center dot center dot I-Ph-NH2 halogen bonding switches off the red RTP from S-2I/I-Ph-NH2 hgDCs, whereas the stable halogen-bonded S-2CN center dot center dot center dot I-Ph-NH2 ensures red RTP from S-2CN/I-Ph-NH2 hgDCs remains unchanged. A security protection luminescence pattern by using these different HCl-responsive RTP behaviors was designed.