Synthesis and properties of thieno[3,2-b]thiophene appended triarylamine radical cations: Near-infrared absorbing dye with absorption beyond 1400 nm

Two triphenylamines with thieno [3,2-b] thiophene units were designed and synthesized. The radical cations obtained by the one-electron oxidation of these amines show a significant absorption in the near-infrared region. In particular, the derivative with three hexyl groups has excellent solubility, and its radical cation has a maximum absorption wavelength above 1400 nm. DFT calculations support these experimental results. A novel design strategy for NIR-II dyes is described.