Modulating Room-Temperature Phosphorescence through the Synergistic Effect of Heavy-Atom Effect and Halogen Bonding

Organic room-temperature phosphorescence (RTP) materials have been paid great attention for their promising applications in anticounterfeiting, optical device, and bioimaging. However, owing to inefficient intersystem crossing (ISC), it still remains a challenge to develop organic RTP materials with both high quantum yields (Phi(p)) and long lifetime (tau(p)). Herein, a reasonable strategy is presented to modulate and balance the Phi(p) and tau(p) through the synergy effect of halogen bonding and heavyatom effect (HAE). Modulated RTP properties are successfully achieved by the introduction of halogen atoms into 4-(9-Hcarbazol-9-yl) benzonitrile due to enhanced ISC. Especially, CzBzBr shows the highest Phi(p) of 23.50% and CzBzCI exhibits the longest tau(p) of 607.4 ms. The excessive HAE of the bromine atom decreases the tau(p) of CzBzBr, while moderate HAE of the chlorine atom endows CzBzCI with both high Phi(p) and long tau(p). In addition, the halogen bondings lead to specific halogen-mediated molecular cluster packing, further suppressing nonradiative transition for ultralong RTP emission. Through simple physical co-crystallization with adjusting the mass ratio of CzBzCl/CzBzBr, co-crystals with modulated RTP properties and white-light emission phenomena are obtained. Our study provides a rationale method to develop modulated high-efficiency RTP materials, which will expand their practical applications.