Two-photon absorption and up-converted fluorescence of novel triphenylamine-based oligomers

Three new conjugated oligomers (referred to as P1, P2 and P3), of “D–π-A” structure with the same donor group of 4-methyl triphenylamine but different acceptor groups such as naphthalene for P1, dibenzothiophene for P2, and dibenzofuran for P3, were synthesized and characterized. The linear optical properties, including absorption and one-photon induced fluorescence, fluorescence quantum yield (Φ) and lifetimes of the oligomers are reported. Two-photon absorption (TPA) properties were measured by open-aperture Z-scan techniques, while two-photon induced fluorescence (TPF) behaviour was recorded using a CCD spectrosensitometer, employing a Ti:sapphire femtosecond laser pulse. It was found that P1 displayed the greatest two-photon absorption coefficient (β) due to its larger intermolecular charge transfer and stronger interactions between donor and acceptor groups. In contrast, P3 exhibited strongest one- and two-photon fluorescence due to its dibenzofuran acceptor group possessing more preponderant radiation dynamics, in comparison with its dibenzothiophene- and naphthalene-based counterparts.