Two-photon photophysical properties of tri-9-anthrylborane

Boron-containing π-conjugated chromophores with unique electronic structures are potent in electro-optical applications, fluorescent chemsensoring and biolabelling. We have done spectroscopic and computational studies on tri-9-anthrylborane (An3B) aiming at providing a deeper insight into its photophysical properties. The fluorescent properties are found to depend strongly on solvent polarity, whereas the 2-photon absorption cross-section with a maximum of ∼110 GM at 805 nm (in n-hexane) shows little solvent dependence. The spectroscopic results combined with the theoretical analyses reveal that the lowest excited state is both 1- and 2-photon allowed, while the second lowest excited state is optically dark and strongly 2-photon allowed. This unique electronic structure gives rise to considerably large 2-photon absorption cross-sections for An3B over a wide spectral range.