Photoresponsive crown ethers. 10. Metal complexation by light‐switched crown ethers immobilized in polymer matrices

Abstract

Abstract The crosslinked polystyrene beads which immobilized two terminal azophenoxide groups of an azobenzene‐crown(24‐crown‐8)‐azobenzene unit were synthesized. The polymer beads adsorbed Cs + in the dark while they rapidly released Cs + into the solution under UV‐light irradiation, and the photoresponsive complexation occurred reversibly. On the other hand, the crosslinked polystyrene beads which immobilized one terminal azophenoxide group of an azobenzene‐crown (24‐crown‐8) unit scarcely (or only to a smaller extent) exhibited such a photoresponsive behavior. Similarly, the polymer beads which immobilized two terminal azophenoxide groups of an azobenzene‐crown (18‐crown‐6) azobenzene unit reversibly adsorbed and desorbed K + in response to UV‐light irradiation. The novel photoresponsive behavior is ascribed to a conformational distortion of the crown rings which induced by the photoisomerization of the azobenzene moiety, although the photoinduced polarity change of the polymer beads is not completely ruled out. The results suggest that the polymer support is useful as a “fixed point” to enforce the conformational changes of immobilized functional molecules.