Characterisation of ‘sandwich’ charge-transfer complexes composed of bis-anthracene donors and aromatic acceptors

Abstract

Properties of ‘sandwich’ charge-transfer (CT) complexes composed of bis-anthracene host compounds, in which two anthracences are connected by an anthraquinone spacer, and various aromatic acceptors have been systematically studied. Complexation stronger than that seen in monomer model compounds was observed in all cases. Thermodynamic analysis revealed that this enhanced binding to acceptors is due to larger enthalpic gain accompanied by a lower entropy loss effected by preorganization of the host. The major factor that determines the association constants is not the strength but the steric features of acceptor. Binding constants for fluorenones with nitro residues in the bay region are smaller because of the bulkiness of the substituents. It has been established that the CT complexes are of the weak b_π–a_π type from the analysis of the CT absorption energy. Complexation-induced chemical shifts in the ¹H NMR spectra indicate highly oriented guest inclusion and have revealed some geometrical features of the complexes.