The synthesis and one- and two-photon optical properties of dipolar, quadrupolar and octupolar donor-acceptor molecules containing dimesitylboryl groups

Two series of related donor-acceptor conjugated dipolar, pseudoquadrupolar (V-shaped) and octupolar molecular systems based on the p- dimesitylborylphenylethynylaniline core, namely, 4-(4- dimesitylborylphenylethynyl)-N,N-dimethylaniline, 4-[4-(4- dimesitylborylphenylethynyl)phenylethynyl]-N,N-dimethylaniline, 3,6-bis(4-dimesitylborylphenylethynyl)-N-n-butylcarbazole and tris[4-(4-dimesitylborylphenylethynyl)phenyl]amine, and on the E-p-dimesityiborylethenylaniline motif, namely, E-4-dimesitylborylethenyl-N,N- di(4-tolyl)aniline, 3,6-bis(E-dimesitylborylethenyl)-N-n-butylcarbazole and tris(E-4-dimesitylborylethenylphenyl)amine have been synthesised by palladium-catalyzed cross-coupling and hydroboration routes, respectively. Their absorption and emission maxima, fluorescence lifetimes and quantum yields have been obtained and their two-photon absorption (TPA) spectra and TPA cross-sections have been examined. Of these systems, the octupolar compound tris(E-4-dimesitylborylethenylphenyl)amine has been shown to exhibit the largest TPA cross-section among the two series of approximately 1000 GM at 740 nm. Its TPA performance is comparable to those of other triphenylamine-based octupoles of similar size. The combination of such large TPA cross-sections and high emission quantum yields, up to 0.94, make these systems attractive for applications involving two-photon excited fluorescence (TPEF).