The effect of uv irradiation on the solid solutions of MTHF and EtOH containing CuCl with HCl has been investigated.
The axial ESR spectra observed before uv irradiation at 73 K for these solutions indicate that Cu(II) ions exist
in such a way that the unpaired electron density locates on 3d9 orbital in the coordination structure associated with the
ligand molecules. The new ESR signals observed after uv irradiation is inferred to Cu(II) ions of a transformed ligand
structure that is formed via an exciplex “adiabatically”. We infer that the new species induced by uv irradiation forms
strong covalent bonds between Cu(II) ions and the ligand. The formation of the exciplex has also been evidenced by the
absorption and emission properties for the same solutions at 77 K. Three types of emissive exciplexes have been proposed.