Conjugated thiophenoazomethines: electrochromic materials exhibiting visible-to-near-IR color changes

Conjugated thiophene azomethines with different degrees of polymerization were prepared. Both the molecular weights and polydispersity indices were consistent with step-growth polymerization instead of the expected dynamic component exchange by transimination. It was found that the absorbance of the neutral compounds could be tuned between 450 and 630 nm, contingent on their degree of conjugation. The absorbance of the oxidized state was also found to vary between 490 nm and 1111 nm as a function of structure. The electrochromic properties of the conjugated azomethines were assessed in solution. An electrochromic device was prepared from one of the polyazomethines and it was switched between blue and colorless states with a bias of +/- 2 V. Visible-to-NIR color switching of the electrochromic device was possible under ambient conditions.