High‐Performance Electrofluorochromic Devices Based on Electrochromism and Photoluminescence‐Active Novel Poly(4‐Cyanotriphenylamine)

A novel electrochromism (EC) and photoluminescence (PL)‐active poly(4‐cyanotriphenylamine) (CN‐PTPA) is prepared by oxidative coupling polymerization from 4‐cyanotriphenylamine (CN‐TPA) using FeCl3 as an oxidant. The high‐performance electrofluorochromic (EFC) devices using CN‐PTPA thin film with photoluminescent quantum yield of 21.9% as active layer are readily fabricated and reveal the highest fluorescent contrast ratio (I off/I on) of 242 between the fluorescent (neutral) state and the non‐fluorescent (oxidized) state, rapid response time shorter than 0.4 s, and excellent EFC stability longer than 9000 s. Furthermore, by introducing viologen into electrolyte as a counter EC layer for charge balance, the resulting EFC device exhibits notable improvement in reducing oxidation potential (from 2.30 V to 1.55 V) and switching recovery time (from 78 to 38 s) with enhanced fluorescent contrast ratio during pulse on/off multi‐cyclic scanning. These results demonstrate that incorporation of the EC and PL‐active CN‐PTPA is a facile and feasible approach to prepare highly efficient EFC devices.