A new dithienylethene dimer with terminal tertiary amine redox centers: Electrochemical, UV–vis–NIR spectral and electronic transfer charges induced by a stepwise photochromic process

Abstract

Photochromic diarylethene dimers (R-DTE-CCCC-DTE-R, R = benzene, 1oo; R = triphenylamine, 2oo; DTE = dithienylethene) with remarkable stepwise photochromic process were synthesized successfully. Dimer 2oo, whose two terminal redox-active triphenylamine centers were separated by two photochromic DTE-acetylide moieties, could accomplish photoswitchable charge delocalization between the N⋯N electro-active centers. Upon UV-light irradiation, due to the progressive increase of π-conjugated systems as the order of 2oo → 2co → 2cc, the electronic interaction of two N-centers in 2oo was increasingly facilitated following the stepwise photocyclization. Furthermore, for monocationic species [2oo]+/[2co]+/[2cc]+, their absorption strength was gradually increased during the conversion of [2oo]+→[2co]+→[2cc]+, which demonstrated that the extent of charge delocalization along the molecular backbones was progressively enhanced during the stepwise photocyclization. The lower electronic density of reactive carbon atoms during the oxidation of N0 to N+ could result more difficult photocyclization reaction to produce oxidized species [2oo]2+/[2co]2+. Additionally, compound 2 exhibited eight switchable states through stepwise photochromic and reversible redox processes.