Two-photon excited fluorescence from ground-state charge-transfer cocrystals of acridine and 1,2,4,5-tetracyano-benzene

Near-infrared two-photon absorption (TPA) molecules designed based on intramolecular charge-transfer (CT) interactions have been widely investigated during the last few decades; however, studies on supramolecular TPA materials based on intermolecular CT interactions are quite rare. In this work, cocrystals of acridine and 1,2,4,5-tetracyano-benzene were successfully prepared by self-assembly. The cocrystals show yellow emission centered at ∼540 nm with a solid-state photoluminescence quantum yields (PLQY) of 22.48%. Two-photon excited fluorescence (TPEF) measurements show that the cocrystals display wide-window TPEF that is absent in their individual components. Optical absorption analysis indicate that the fluorescence is originated from excitation from the ground states to CT exciton states instead of exciton states of donor or acceptor molecules. This work may facilitate further two-component nonlinear optical material design and applications.