A novel member of a benzo-annulated oxocarbon family

Abstract

An unusual reactivity channel of semisquaraines is disclosed, yielding a novel type of oxocarbon derivative via facile synthetic procedure. The compound exhibits extremely rare “double” redox-ambipolarity (strong stabilization of both mono- and di- oppositely charged ionic states) sustained by a relatively small conjugated system. Remarkable “atom-economic” structure of the oxocarbon provides two orthogonal channels for charge/spin delocalization combined via the central 6-membered ring, which may be both in aromatic or in quinoidal state, thereby controlling charge redistribution and ensuring stabilization of five redox-states. Radical-cation shows no destruction in 24 h; half-life of the radical-anion is 2.5 h. Stability of multiple redox states in combination with intensive UV-Vis-NIR absorption gives rise to pronounced electrochromic behaviour that makes the novel oxocarbon derivative potentially interesting for application in electrochromic displays, in photovoltaics as well as a redox indicator, e.g., for sensing metal ions (shown experimentally). In the crystal state, the compound demonstrates high thermal stability and is prone to form π-stacked 1D supramolecular structure.