X-Aggregation Enhanced Room Temperature Phosphorescence from Terphenylamine.

Organic room temperature phosphorescence (RTP) materials have drawn wide attention because of their unique photoluminescence performances. As is known, their molecular aggregation shows determined influences on their RTP performances. However, the regulation mechanism of the molecular aggregation is still unclear. Herein, the structure-aggregation dependence of organic RTP materials is studied in detail. When introducing methyl and constructing a constrained configuration, the resultant compounds show improved long-persistent luminescence performances. The terphenylamine (TPA) derivatives bearing methyl groups exhibit a prolonged RTP lifetime of about 68-410 ms. As the configurations are constrained stepwise, the RTP lifetimes of TPA, PhCz, and ICz also increase gradually. In contrast, methoxyl and tert-butyl result in a significant shortening of the RTP lifetime to about 110-312 ms and even quenching of RTP. It is found that the introduction of electron-donating groups and the construction of constrained configuration are beneficial for forming regular X-aggregation and rigid molecular packing, while unconstrained bulky groups would result in multiple conformations and disordered molecular arrangement. The X-aggregation could enhance both the intermolecular charge transfer and the restriction on molecular motion, which shows promoting effects on the intersystem crossing processes and suppressed nonradiative decay, resulting in long-lived RTP emission.