Synthesis, Fluorescence, and Two-Photon Absorption Properties of Push–Pull 5-Arylthieno[3,2-b]thiophene Derivatives

Three series of novel push–pull 5-arylthieno[3,2-b]thiophene derivatives functionalized with potent electron-withdrawing terminal moieties have been synthesized in moderate to excellent yields by Suzuki coupling followed by Knoevenagel condensation. These novel chromophores show intense absorption in the near-UV region through to the orange visible region, related to a strong intramolecular charge-transfer transition. By combining a strong donor and acceptor, large fluorescence quantum yields were achieved as well as large two-photon absorption responses. Interestingly, due to the improved rigidity and electronic delocalization provided by the thienothiophene moiety (as compared with the bithiophene unit), higher one- and two-photon brightness values have been achieved. As a result, several new fluorescent dyes showing enhanced brightness and tunable fluorescence (ranging from the blue to the NIR region) have been obtained that have potential for bioimaging applications.