Biluminescence via Fluorescence and Persistent Phosphorescence in Amorphous Organic Donor(D₄)–Acceptor(A) Conjugates and Application in Data Security Protection

Abstract

Purely organic biluminescent materials are of great interest due to the involvement of both singlet and long-lived triplet emissions, which have been rarely reported in bioimaging and organic light-emitting diodes. We show two molecules 3,4,5,6-tetraphenyloxy-phthalonitrile (<b>POP</b>) and 3,4,5,6-tetrakis-<i>p</i>-tolyloxy-phthalonitrile (<b>TOP</b>), in which <b>POP</b> was found to exhibit fluorescence and persistent room-temperature green phosphorescence (pRTGP) in the amorphous powder and crystal states. Both <b>POP</b> and <b>TOP</b> show aggregation-induced emission in a tetrahydrofuran–water mixture. We found in single-crystal X-ray analysis that intra- and intermolecular lp­(O)···π interactions along with π­(C = C)···π­(CN), hydrogen bond (H–B), and C–H···π interactions induce a head-to-tail slipped-stack arrangement in <b>POP</b>. In addition, the X-ray structure of <b>TOP</b> with a slipped-stack arrangement induced by only π­(CC)···π­(CN) and H–B interactions shows dim afterglow only in crystals. These indicate that more noncovalent interactions found in <b>POP</b> may reinforce relatively efficient intersystem crossing that leads to pRTGP. Given the unique green afterglow feature in amorphous powder of <b>POP</b>, document security protection application is achievable