A series of host-guest coordination polymers containing viologens: syntheses, crystal structures, thermo/photochromism and factors influencing their thermo/photochromic behaviors.Responsive molecular chromic materials have shown potential applications in molecular optical switches and sensor devices as they undergo reversible colour changes upon application of external stimuli.  Herein, six host-guest coordination polymers 1-6 and one organic supramolecular compound 7 containing viologens have been synthesized under hydrothermal conditions.  Compound 1 shows thermochromic behavior with a colour change from green to blue upon heating at 150 °C in air.  Thermo/photochromic mechanisms have been investigated by infrared spectroscopy, powder X-ray diffraction analysis, UV-vis absorption spectroscopy, electron paramagnetic resonance spectroscopy, and X-ray photoelectron spectroscopy.  The results demonstrate the generation of viologen radicals caused by thermo/photo-induced electron transfer.  Our findings demonstrate the possibility of applying thermo/photochromic coordination polymers in molecular devices.
THERM