Triphenylamine/4,4′-Dimethoxytriphenylamine-Functionalized Thieno[3,2-b]thiophene Fluorophores with a High Quantum Efficiency: Synthesis and Photophysical Properties

A wide series of 10 new triphenylamine (TPA)/4,4′-dimethoxytriphenylamine (TPA(OMe)₂)-functionalized thieno[3,2-b]thiophene (TT) fluorophores,4a-eand5a-e, bearing different electron-donating and electron-withdrawing substituents (-PhCN, -PhF, -PhOMe, -Ph, and -C₆H₁₃) at the terminal thienothiophene units were designed and synthesized by the Suzuki coupling reaction. Their optical and electrochemical properties were investigated by experimental and computational studies. Solid-state fluorescent quantum yields were recorded to be from 20 to 69%, and the maximum solution-state quantum efficiency reached 97%. Moreover, the photophysical characterization of the novel chromophores demonstrated a significant Stokes shift, reaching 179 nm with a bathochromic shift. They exhibited tuning color emission from orange to dark blue in solution and showed fluorescence lifetime reaching 4.70 ns. The relationship between triphenylamine (TPA)/4,4′-dimethoxytriphenylamine (TPA(OMe)₂)-derived triarylamines and different functional groups on thieno[3,2-b] thiophene units was discussed.