Novel triazine-centered viologen analogues for dual-band electrochromic devices

Dual-band electrochromic device (Db-ECD) can tune visible and near-infrared (NIR) radiation independently. The Db-ECDs have inspired considerable interest for their potential applications in smart windows and camouflage. Organic small molecules and polymers were examined carefully though, exploring organics with dual-band electrochromism is still challenging. Herein, the triazine-centered viologen analogues, 2,4,6-tri(pyridyl-4-propyl)-1,3,5-triazine bromide (TPPT) and 2,4,6-tri(pyridyl-4-benzyl)-1,3,5-triazine bromide (TPBT) show excellent dual-band electrochromic behaviors with high dynamic contrasts (66.63% at 887 nm and 50.71% at 600 nm for TPPT, and 59.79% at 900 nm and 66.90% at 600 nm for TPBT, respectively). The Db-ECDs fabricated via gel electrolyte mixed with TPPT or TPBT can work at a low driving voltage down to ∼0.6 V, rendering a high coloration efficiency (up to 230.94 cm 2  C -1 ) in the NIR region , the absorbance difference at 1037 nm reaching up to 2.58 for TPPT. This work sets the stage for novel organic materials of dual-band electrochromic gadgets.