Novel dithienoazaborine viologen derivatives with two different π-conjugated extensions for electrochromic application

Abstract Two kinds of dithienoazaborine viologen derivatives (3a and 3b) with different π-conjugated extensions were synthesized via late-stage functionalization of dithienoazaborine precursor (BNDT). In sharp contrast to 3a (conjugation I), 3b (conjugation II) showed red-shifted absorption (∼468 nm), narrower optical bandgap (2.65 eV), and aggregation-induced emission (AIE) property. Meanwhile, 3b-based electrochromic device (ECD) showed longer switching times (21.6 s for coloration and 34.9 s for bleaching), higher color contrast ratios (21.3%), higher coloration efficiency (13.29 cm2/C), as well as better stability compared with 3a-based ECD. In addition, an electronic information (E-information) tag and a flexible ECD were assembled using 3b, further manifesting its potential applications in display areas. The research not only expands the structural types of viologen derivatives but also compares the effects of different conjugation on the properties of viologen derivatives for the first time, which may provide a feasible way to design new electrochromic materials.