Triplet Spin Exchange in Some Ion Radical Salts

Abstract

Studies of the effects of spin exchange on the electron paramagnetic resonance spectra of the ion radical salts (φ3PCH3)+(TCNQ)2-, (φ3AsCH3)+(TCNQ)2-, (Cs+)2(TCNQ)3= and (morpholinium)+(TCNQ)- have been carried out. Exchange parameters have been determined from all three limiting approximations relating to line width and line separation of the exchange-modified Bloch equations. While in general the exchange frequency ν can be expressed as ν=ν0 exp (— ΔE/kT), different values of ν0 and ΔE for a given material are obtained depending upon the limiting approximation employed. This ``anomalous'' exchange-narrowing behavior is discussed in terms of the current model for these triplet-state systems with particular emphasis upon the possible complicating features presented by the presumed existence of triplet excitons.