Effective Approach toward Selective Near-Infrared Dyes: Rational Design, Synthesis, and Characterization of Thieno[3,4-b]thiophene-Based Quinoidal Oligomers

This paper describes syntheses, photophysical properties, and electrochemical characteristics of three thieno[3,4-b]thiophene (TT)-based quinoidal oligomers OnTTO. The rigid planar backbones of these oligomers give the molecules narrow absorption bands, and the main absorption bands were significantly red-shifted when the TT units were extended and demonstrated wide transparent windows. The compound O4TTO was found to possess strong absorption in the near-infrared (NIR) region approaching 1200 nm but remained transparent in the visible region. Electrochemical experiments have shown that the energy band gaps gradually narrow when the TT units are increased. Optical properties predicted by density functional theory calculations are in good agreement with the experimental optical results. These dye molecules could be promising candidates for future NIR photodetectors, filters, and bioimaging technologies.