Large cyano- and triazine-substituted D-π-A-π-D structures as efficient AIEE solid emitters with large two-photon absorption cross sections

A series of new large π-conjugated molecules including diphenylamine and carbazole have been synthesized and characterized (3a-c). All compounds display aggregation-induced emission enhancement (AIEE) characteristics: exhibiting weak fluorescence in pure THF, while a significant AIEE effect is observed in mixtures with a water fraction (f_w) of 90% with a sharp increase in fluorescence intensity. Combining intramolecular charge transfer (ICT) characteristics and AIEE features, 3a-c are intense solid emitters (589 nm, 546 nm and 556 nm, respectively) with high quantum efficiencies of 18.1%, 27.4% and 14.9%, respectively. Their two-photon absorption (2PA) properties have been investigated using the open-aperture Z-scan technique, and the values of the 2PA cross section at 800 nm for 3a-c are 1363 GM, 413 GM and 5782 GM, respectively. Their excellent 2PA properties and solid quantum efficiencies pave the way for their potential use in biophotonic and optoelectronic applications.