Rapid construction and intrinsic mechanism of host-guest room temperature phosphorescence systems

The construction of small molecule host-guest room temperature phosphorescence (RTP) systems usually involved melting, which required low melting point and excellent thermostability for host materials, limiting the selection range of host materials. Here, 2-(3-(9H-carbazol-9-yl)benzyl)malononitrile (L-DCN) and 2-(3-(5H benzo[b]carbazol-5-yl)benzyl)malononitrile (m-BCzCN) were prepared by self-made carbazole and 2-naphthylamine. Based on the side chain with multiple cyanide groups and similar molecular structures between L-DCN and m-BCzCN, crystallization ability of L-DCN and the compatibility between L-DCN and m-BCzCN were significantly enhanced. Thereby, rapid construction of long-lived host-guest RTP systems could be achieved by organic solvent dissolution and rapid evaporation of L-DCN and m-BCzCN. To explore the effects of trace carbazole impurities, DCN with the same structure with L-DCN was preapared by choosing commercial carbazole. Moreover, RTP performance of L-DCN was further optimized by host-guest doping and tuning the mass ratios between polyvinyl alcohol (PVA) and L-DCN. Compared with crystals DCN, RTP performance of 1 % L-DCN@PVA was not significantly improved, but 1 % L-DCN/m-BCzCN constructed by dissolution and rapid volatilization showed almost equivalent afterglow lifetimes, with RTP lifetimes of 435.37 ms and quantum yield (ΦP) of 0.06, achieving the expected goal. Finally, advanced encryptions were successfully constructed based on the different luminescent properties of L-DCN in PVA films at different doping concentrations. •The trace carbazole isomer effect had been further clarified.•Pure organic long-lived RTP materials had been successfully prepared.•The work provided a simple preparation process for host-guest doping.•The underlying mechanism behind RTP was discussed in detail.