D-A-D-A-D conjugated pyrenoviologens for electrochromism, electrofluorochromism, and detection of picric acid

π-Conjugated donor-acceptor-donor-acceptor-donor (D-A-D-A-D) type pyrenoviologens (PyV²⁺), with the 2,7 positions of pyrene serving as connection bridges, were synthesized through S_N2 reactions. Specifically, pyrenoviologen 3c was modified with a methylnaphthalene group, while 3a and 3b were modified with methyl and benzyl groups, respectively, for comparison. These pyrenoviologens exhibit reversible redox properties and strong fluorescence emission. Electrochromic devices (ECDs) were prepared using pyrenoviologens as the active materials. Notably, naphthalene-containing pyrenoviologen 3c, with its D-A-D-A-D conjugated structure, possesses more stable free radicals, enabling it to maintain the radical color for a longer duration after power loss. A series of color-changing devices were successfully assembled. Due to the strong fluorescence of pyrenoviologens and the unique electron transfer effect between them and picric acid (PA), a sensor film with good selectivity and high sensitivity for PA in aqueous solution was prepared using pyrenoviologens as the fluorescent probe. Specifically, 3c exhibited the highest sensitivity to PA due to its lowest energy gap. The introduction of the D-A-D-A-D structure is a strategic approach to enhancing photoelectric performance and broadening the application of viologens.