Potential photoresponse of membranes containing a lipophilic crowned spirobenzopyran
Potential response and its photoresponse for plasticized-poly(vinyl chloride) membranes containing a lipophilic crowned spirobenzopyran were surveyed and compared with those for membrane systems of a spirobenzopyran deriative not carrying any crown ether moiety. On UV-light irradiation, an intriguing type of time-course change was found with the membrane potential for the crowned spirobenzopyran system in the presence of alkali metal ions, i.e., the potential first increases and then decreases. The photoresponse profile for the crowned spirobenzopyran system was affected considerably by the sort of metal ions and the pH conditions of aqueous phases. This phenomenon is explained by an ion-exchange mechanism specific to crowned spirobenzopyran, that is, fast proton exchange followed by slow metal-ion exhange of its merocyanine form. The system for the corresponding spirobenzopyran without crown ether moiety exhibited a steady potential photoresponse that depends on the pH conditions of aqueous phases.