Photoinduced membrane potential changes. Poly(vinyl chloride) membranes entrapping a photoresponsive bis-(15-crown-5) derivative

Plasticized poly(vinyl chloride) (PVC) membranes entrapping photoresponsive bis-(15-crown-5) with an azo-linkage (2) and its monomeric analogue (1) were prepared for the purpose of regulating their membrane potential by u.v. or visible light irradiation. The azobenzene moieties of (1) and (2) were found to undergo photochemical trans-cis isomerization reversibly in the membrane matrix. Alternating u.v. and visible light irradiation induced a significant reversibly potential change across the PVC-(2) membrane but did not for PVC-(1) membrane. Large potential shifts were induced by photoirradiation in the presence of KCl or RbCl, while the potential shifts, if observed, were small (-2.5 mV or less) in the presence of LiCl or NaCl. The photoinduced potential changes across the membranes were explained in terms of the change in binding ability of (2), resulting from trans-cis photoisomerization, for K⁺ and Rb ⁺ at the membrane-solution interface. In other words the surface potentials at the two membrane-solution interfaces were considered to be perturbed by photoirradiation.