Photoinduced membrane potential changes. Bi‐ionic potential across poly(vinyl chloride) membranes entrapping a photoresponsive bis(15‐crown‐5) derivative and the effects of photoirradiation

Bi‐ionic potential (BIP) across poly(vinyl chloride) membranes containing azobenzene‐modified bis(15‐crown‐5) was measured in the presence of alkali‐metal chlorides. The BIP measurements revealed the cation selectivity sequence of the membranes (K⁺ > Rb⁺ > Cs⁺ ≫ Na⁺ > Li⁺), which agreed well with the potentiometric selectivity order of 15‐crown‐5–based ion‐selective electrodes developed so far. UV‐light irradiation induced the positive or negative shift of BIP. The magnitude and sign of the photoinduced potential shift depended considerably upon the kind and concentration of electrolytes and, as well, the direction from which the membrane was irradiated. The results were explained in terms of the surface‐potential changes induced by light irradiation.