A novel member of the benzo-annulated oxocarbon family

Abstract

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