ESR analysis of columnar structure in conductive LB films of TCNO salts with alkylpyridinium and its derivatives

Abstract

The temperature dependent spin susceptibility of the LB films of a TCNQ salt with an alkylpyridinium was found to be explained by the random-exchange Heisenberg antiferromagnetic chain model, indicating the development of 1D spin chains in the system. The ESR spectra of the films at the X and K bands show clear out-of-plane anisotropy. The analysis of these line shapes using the spectrum simulation method reveals that the linewidth anisotropy is dominated by the exchange-narrowed secular dipolar width peculiar to quasi-1D spin systems. This result provides further evidence for the development of the 1D columnar structure of TCNQ molecules, and suggests that the chain axis lies in the film plane. In addition, the analysis yields the orientation of TCNQ molecules, which is consistent with the formation of the columnar structure.