Dithienopyrrole compound with twisted triphenylamine termini: Reversible near-infrared electrochromic and mechanochromic dual-responsive characteristics

Abstract

A dithieno[3,2-b:2′,3′-d]pyrrole-based luminogen 1 has been synthesized by appending two twisted triphenylamine units to the rigid conjugated dithieno[3,2-b:2′,3′-d]pyrrole core. This compound exhibits reversible mechanochromic luminescence in the solid state and near-infrared electrochromic switching behavior in solution. A reversible switching in fluorescence color between yellow-green and green can be observed through mechanical grinding and vapor fuming of solid powdered 1, which involves an interconversion between a crystalline form and an amorphous phase according to X-ray diffraction analysis. The associated oxidized species of 1 show intense redox-switchable near-infrared absorption and different fluorescence colors in solution in spectroelectrochemical and luminescence measurements. Density functional theory calculations have confirmed that there is considerable electron delocalization between the dithieno[3,2-b:2′,3′-d]pyrrole linker and two triphenylamine redox-active termini during the oxidation process.