Pluri-dimensional hydrogen-bonded networks of novel thiophene-introduced oligo(imidazole)s and physical properties of their charge-transfer complexes with TCNQ

Novel π-extended oligo(imidazole)s composed of imidazole and thiophene ring systems, bis(imidazolyl)thiophenes 1-4, were synthesized as new building blocks for electron-donor molecules having diverse hydrogen-bonding directionalities in order to explore hydrogen-bonded charge-transfer complexes and supramolecular assemblies. The cyclic voltammetry of these compounds showed increase of electron-donating ability compared with those of 2,2′- and 4,4′-biimidazoles. In the crystal structure, 1, 2 and 3 exhibited multi-dimensional hydrogen-bonded networks via solvent molecules including the π-π interaction. Charge-transfer complexes of 1, 2 and 4 with TCNQ were characterized as partial charge-transfer complexes with segregated stacks. The compressed pellets of the TCNQ complex of 2 showed a high electrical conductivity (σ_rt=5.2×10⁻² S cm⁻¹) at room temperature with semiconducting behavior (activation energy, E_a=71 meV).