B‐N Fused Anthracene as Functional Linker for π‐Extended Viologens: Near‐IR Emission and Electrochromism

Abstract

Abstract As prototypical organic electrochromic materials viologens have been extensively studied in display technologies, smart materials, and energy storage applications. Their properties can be fine‐tuned by introducing different substituents on the pyridine rings, fusion with heteroatoms, or insertion of π–conjugated linkers. In this article we study the effect of B‐N fused dipyridylanthracene (BDPA) as a novel linker unit in viologens on the electronic structure, optical properties, and electrochromic characteristics. Quaternization of pyridyl‐functionalized BDPA ( 1Py ) by N‐methylation or complexation with B(C 6 F 5 ) 3 as a powerful Lewis acid gives rise to two fundamentally different π‐extended viologens, dicationic [ 1Py‐Me ](PF 6 ) 2 , and the neutral complex 1Py‐BCF . We investigate the effect of these different quaternization methods on the LUMO energy, band gaps, absorption and emission, and the self‐sensitized reactivity toward oxygen. We also demonstrate facile electrochemical reduction to singly and multiply reduced species. Spectroelectrochemical and computational studies reveal formation of strongly colored doubly reduced species with a closed shell electronic configuration and prominent quinoidal delocalization. The corresponding radical anions give rise to absorptions in the near‐IR. A prototype electrochromic device with 1Py‐BCF as the redox‐active material is also presented.