Heterocyclic Quinodimethanes

This chapter describes a series of heterocyclic quinodimethanes mainly containing O, N, S and Si atoms in their frameworks with either closed- or open-shell electronic structures in the ground state. Their syntheses, structural characterizations and chemical and physical properties are comprehensively reviewed. Some of them are used as materials for dyes/pigments and semiconductors for organic electronics. Some of them show an open-shell singlet diradical character with unusual properties. The purpose of this chapter is to provide fundamental understanding on the structure-property relationships of quinoidal π-conjugated compounds and give some insight into the rational design of such molecules with desirable properties.