Photoconductivity of degassed ethers as a function of their purity

Abstract

The pulse d.c. photoconductivity (PC) of the vacuum-degassed ethers tetrahydrofuran (THF), ethyl ether (Et₂O) and 1,4-dioxane was investigated. It was found that after a light pulse of duration 1 ms in degassed THF or Et₂O the photocurrent rises. A monophotonic ionic photodissociation is responsible for the charge generation since the photosignals were proportional to the amount of absorbed light. The photocurrent signals decreased exponentially with first-order rate constants which decreased linearly with the decreasing voltage applied between the platinum electrodes. This might indicate that the fairly stable photoproduced ions disappear mainly in the electrode discharge reactions. The bulk recombination, which is probably preceded by a monomolecular or pseudomonomolecular rearrangement (since this is a process also well described by an exponential equation) did not exceed about 10% of the total ion consumption under the conditions used. After examining different methods of purification of the ethers studied it was found that the phenomenon was caused by electron acceptor impurities, which were mainly the products of the oxidation of ethers. In the case of 1,4-dioxane the PC signals were hardly detectable, since the lower polarity of this solvent did not favour ionic dissociation of the ion pairs which are probably also produced. An improved method of purification of these ethers is proposed.