Synergism of photocycloaddition and photoinduced electron transfer for multi-state responsive materials with high-stability and reversibility.

A dual-photoresponsive coordination polymer displaying color-distinguishable olefin/cyclobutane-linked pyridinium radical states through photoinduced electron transfer and photocycloaddition has been successfully assembled based on the monoquaternized trans-1,2-bis(4-pyridyl)ethylene and electron-rich benzenetetra-carboxylate anion. The synergy of charge-transfer and cation-π interactions within the framework endows the compound with excellent stability toward high temperature (350 °C), acidic/basic environments (pH = 2-12) and organic solvents. Reversible recovery from the radical states to their initial states, and reverse-cyclization can be achieved upon heat-treatment.