Photo-switchable molecular devices based on metal-ionic recognition

A novel calix[4]arene derivative, bearing two spirobenzopyran moieties in the lower rim, can recognize lanthanide ions. Alternating irradiation with ultraviolet and visible light controls the ligand-to-metal charge transfer (LMCT) and energy transfer of the host–Eu3+ complexes. Thus, fluorescence of Eu3+ can be switched on and off through light. The system may be applied as molecular logic switches.