Synthesis, optical properties and ultrafast dynamics of a 2,1,3-benzothiadiazole-based red emitter with intense fluorescence and large two-photon absorption cross-section

A new 2,1,3-benzothiadiazole-based red fluorescent compound with a D-A-D type structure was synthesized and characterized. The central 2,1,3-benzothiadiazole core was symmetrically connected via the 4,7-positions with two donor groups in which the 7-position of a fluorenyl ring was substituted with a carbazol-9-yl moiety and the 2-position was substituted by a 5-thienyl moiety. The carbazol moieties were further derivatized by two 2-naphthyl moieties at the 3,6-positions. Femtosecond laser spectroscopic techniques including excited state fluorescence and pump-probe technique investigations, together with steady state absorption and one-photon fluorescence spectra, were employed to systematically investigate the optical properties and ultrafast dynamics of the new compound in tetrahydrofuran solution. It shows a large two-photon absorption cross-section and high fluorescence quantum yield, indicating potential application in two-photon fluorescence imaging field. The ultrafast dynamics results reveal competition between a pure excited state relaxation process and stimulated radiation in the red wavelength region. (C) 2011 Published by Elsevier Ltd.