The synthesis, electrochemical and optical properties of three fluorescent substituted thieno[3,2-b]benzothiophenes (TBT) derivatives, including 3-methoxythieno[3,2-b]benzothiophene (3-MeO-TBT), 2,3-dimethylthieno[3,2-b]benzothiophene (2,3-diMe-TBT), and 6-methoxythieno[3,2-b]benzothiophene-2-carboxylate (6-MeO-TBT-2-COOMe), were investigated. The oxidation potential values varied between 1.40 and 1.20 V/SCE according to the electronic substituent effect, and electropolymerization attempts, performed in 0.1 M LiClO4 acetonitrile solution, led to the formation of very thin films of poly(3-MeO-TBT) and poly(2,3-di-Me-TBT). Electronic absorption spectra, fluorescence excitation and emission spectra, fluorescence quantum yields (ΦF) , lifetimes (τF), and other photophysical parameters of the three new TBT derivatives were measured in DMSO solutions at room temperature. For the methyl-and methoxy-substituted TBT derivatives, the fluorescence emission peak were slightly red shifted relative to that of unsubstituted TBT (Δλem = 1–12 nm) whereas, in the case of 6-MeO-TBT-2-COOMe, a rather strong red-shift (Δλem = 73 nm) was attributed to the existence of a “push-pull” electronic interaction of the MeO and COOMe groups. All ΦF values were rather high, varying between 0.11 and 0.35, according to the substituent effect. Fluorescence decays were mono-exponential and τF values were very short, ranging between 0.11 and 0.30 ns for the substituted TBT derivatives until study.
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This work was, in part, financially supported by the Ministry of Education, Youth and Sports of the Czech Republic (projects MSM 6046137301 and OC176) and by the French Ministry of Foreign Affairs (French-Czech research project Barrande N°03079SF). Dr. C. Lô gratefully thanks the Senegalese Ministry of Education for a Ph.D. grant. Dr. Li Na warmly thanks the ENS of Cachan for a Ph.D. grant.
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