Structural feature of thermo-induced fluorochromism in a 1D zinc coordination polymer. A cross-analysis by PL and FTIR spectroscopy, and DFT formalism

The latest tools for applications in chemical, environmental, and biological sciences are based on stimuli-responsive materials. Due to their easy detectable output, fluorochromic probes able to provide photoluminescence response to a given parameter/analyte are in high demand. Here, we designed a monodimensional coordination polymer by zinc-driven self-assembly of symmetrical N,O mononegative ligands containing a flexible spacer. This easy-to-synthesize polymer exhibits the processability of organic polymers and an interesting emission pattern. By annealing the polymer above the glass transition temperature, a relevant fluorochromism was detected. The emission undergoes to a red-shift, turning its turquoise-blue emission to yellow emission, and accompanied by a decrease of the photoluminescence quantum yield of about 2.5 fold. Guided by a cross-analysis based on X-ray structural study, PL, FTIR data, and DFT calculations we explored the mechanism involved in the thermo-induced fluorochromism. We could associate the phenomenon to a structural rearrangement of the coordination environment, involving the pivotal role of zinc, which in turn leads to a change in the dimensionality of the polymer.