Luminescence properties of “double-stranded staircase” copper(i) halide coordination polymers with N-containing ligands

A set of CuIXL coordination polymers (X = Cl, Br, I; L = derivatives of pyrazine and bipyridine) with double-stranded staircase structures was analyzed by X-ray crystallography and luminescence spectroscopy to find a relationship between the structure and luminescence properties of the polymers. Our measurements have proved that luminescence emission wavelengths varied between 500–750 nm, after the polymers were irradiated by light with a wavelength of 370 nm. Although each coordination polymer has shown different emission maximum, we observed several interesting trends related to the structure of the compounds. There is a clear correlation between the emission maxima and the halide size and/or Cu–X distance, respectively. On the other hand, the substitution of the ligand L (pyrazine derivatives, 4,4′-bipyridine) has no significant contribution to the emission spectra. This observation supports the theory that the halide to metal charge transfer (XMCT) plays a key role in the photoluminescence of staircase polymers.