Starburst Triarylamine Donor-Acceptor-Donor Quadrupolar Derivatives Based on Cyano-Substituted Diphenylaminestyrylbenzene: Tunable Aggregation-Induced Emission Colors and Large Two-Photon Absorption Cross Sections

In this work, we have developed a new class of aggregation-induced emission (AIE) active compounds, in which three electron-donating diphenylamine, phenothiazine, or carbazole groups are connected to the 1, 4-positions of the benzene through bis(alpha-cyano-4-diphenylaminostyryl) conjugation bridges to form three triarylamine quadrupolar derivatives (3 a-c). Their one- and two-photon absorption properties have been investigated. The two-photon absorption (2PA) cross sections measured by the open-aperture Z-scan technique were determined to be 1016, 1484, and 814 GM for 3 a-c, respectively. From this result, the high 2PA properties of these molecules are attributed to the extended pi system and enhanced intramolecular charge transfer from the starburst triarylamine to the cyano group. Moreover, cyano-substituted diphenylamine styrylbenzene (CNDPASB)-based compounds are very weakly fluorescent in THF, but their intensities increase by almost 230, 70, and 5 times, respectively, in water/THF (v/v 90%) mixtures, in which they exhibit strongly enhanced red, orange, and deep yellow fluorescence emissions, respectively. This result indicates that the intramolecular vibration and rotation of these dyes is considerably restricted in nano-aggregates formed in water, leading to significant increases in fluorescence. It was found that the color tuning of the CNDPASB-based compounds could be conveniently accomplished by changing the starburst triarylamine donor moiety. Multilayer electroluminescence devices with TPBI (2,2',2 ''-(benzene-1,3,5-triyl)-tri(1-phenyl-1H-benzimidazole)) electron-transporting layers have been made, with 3a and 3c as a non-doping red-yellow emitter. The preliminary results for these multilayer devices show a maximum efficiency of 0.25%, and electroluminescence (EL) wavelengths around 568 nm. The excellent 2PA and AIE properties of these compounds make them potential materials for biophotonic applications.