ELECTRON-SELF-EXCHANGE REACTIONS IN SOLID-STATE VOLTAMMETRY - THE RADICAL-ANION OF 7,7,8,8-TETRACYANOQUINODIMETHANE IN POLYMER ELECTROLYTES .1.

Voltammetric currents for the oxidation of the lithium salt of the 7,7,8,8-tetracyanoquinodimethane anion radical (LiTCNQ) at Pt microdisk electrodes in network poly(ethylene oxide) (PEO) polymer solvent are substantially larger than currents for its reduction. The difference in currents is interpreted as a combination of electron self-exchange (between TCNQ.-and TCNQ0) and electrostatic migration. The latter is a minor effect in the presence of LiClO4 electrolyte as shown by a transference number (t(TCNQ) analysis. At [LiClO4] less-than-or-equal-to 0.4 M, the product k(ex),1/0-delta-1/0(2) of electron-self-exchange rate constant and hopping distance (squared) for the TCNQ-/0 couple is 1.0 (+/- 0.3) x 10(-6) cm2 M-1 s-1. Assuming delta-1/0 = 9.5 angstrom gives k(ex),1/0 = 1 x 10(8) M-1 s-1 in the polymer solvent, which is 47-fold smaller than k(ex),1/0 in acetonitrile solvent and 7-fold larger than measurable by methods subject to diffusion-controlled collision rate considerations. Physical diffusion is also slow in the polymer solvent and connections of this to k(ex),1/0 are discussed, including encounter rate limitations, longer polymer solvent dipole relaxation times, and longer distance electron transfers.