PHOTOELECTRONIC EFFECTS IN ORGANIC MATERIALS–II. VARIATION OF PHOTOVOLTAGE WITH pH IN CHLOROPHYLL-QUINONE SOLUTIONS

— The photovoltaic effect in ethanolic solutions of chlorophyll a with benzoquinone or hydroquinone has been measured as a function of pH. In acidic media, stable, fast-rising photovoltaic signals of positive sign are obtained. In neutral and basic media, less stable, slower rising photovoltaic signals of negative sign are found. The results in acid media are explained in terms of a photochemical interaction between chlorophyll and either the benzoquinone or hydroquinone producing protons which can then act as the electrode active agent. In basic media, negatively charged radical species, such as the benzoquinone radical-anion, are considered to be the most likely electrode-active species.