Correlations between Photoinduced EPR and Photoconductivity in TCNE—THF Solution Charge-Transfer Complex

Abstract

Reversible photoinduced electron paramagnetic resonance (EPR) signals and photoconductivity were observed when a solution of tetracyanoethylene (TCNE) in tetrahydrofuran (THF) was irradiated in the charge-transfer band of the complex formed between these two compounds. The eleven-line hyperfine structure of the EPR spectrum which was obtained demonstrated the presence of TCNE negative-ion radical. The concentration of this radical was found to be directly proportional to the square root of the light intensity. Second-order decay kinetics were followed when the light was shut off. Both the EPR signal and the photoconductivity rose initially as the square of the time. The latter portions of the growth curves could be fit to the latter portions of a hyperbolic tangential growth curve. From these data a reaction mechanism was proposed. The rate law dn/dt+kn2−αL(1−e−βt)=0, where n is the concentration of radicals, t is the time, k, α, and β are rate constants, and L is the light intensity, described both the photoinduced EPR and the photoconductivity within the limits of experimental accuracy.