Electron‐deficient Indenofluorene‐based Systems: Multicolor and Visible‐to‐near‐infrared (NIR) Electrochromism and OFF‐OFF‐ON Electrofluorochromism

Abstract Multifunctional electrochromic systems with divergent functions are highly sought after but rare and challenging to develop. Here, we report the synthesis and multi‐functional electrochromic behaviour (multi‐colour modulation, visible‐to‐near IR absorption switching, and electrofluorochromism) of electron‐deficient indenofluorene‐based systems. The compounds ( IF 1 ‐IF 5 ) have been obtained via Knoevenagel condensation of indenofluorenone ( IF K ) with various nucleophiles (malononitrile, benzylcyanide, dimethyl malonate, methyl cyanoacetate, benzothiazole‐2‐acetonitrile). IF 1 ‐IF 5 possess strong colours and absorb in the visible region (λ max =295–388 nm). These compounds are electroactive and exhibit two reversible reduction waves (−0.35–−0.88 V and −0.65–−1.30 V vs Ag/AgCl), generating radical anion and dianion systems. For the electrochromic studies, upon applying the one‐electron reduction potential (−0.35 V vs Ag/AgCl), the absorption maximum of IF 1 redshift from 382 nm to 1240 nm ( IF 1 − ⋅), which subsequently blueshifts to 466 & 745 nm (IF 1 2 − ⋅ ) upon increasing to two‐electron reduction potential (−0.65 V vs Ag/AgCl). The color of the solution was switched from green to dark blue and further to light orange. The electrochromic behaviour is highly reversible and cycling. In addition, unlike the non‐fluorescent (IF 1 and IF 1 − ⋅ ) , the two‐electron reduced system (IF 1 2 − ⋅ ) is red‐emissive (λ em =630 nm) due to the combination of radicals leading to the formation of antiaromatic quinoidal π‐conjugated system (IF 1 2 − ) .