Lineshape analysis of the ¹³C Overhauser shift in organic conductors and semiconductors

Abstract

In organic conductors such as (fluoranthene)₂PF₆ or pyrene radical-cation salts, and organic semiconductors such as lithium phthalocyanine, a shift of the conduction-electron spin resonance (CESR) frequency is observed. This so-called Overhauser shift is significant compared with the CESR linewidth and is caused by the averaged hyperfine interaction between the conduction electrons and the nuclei. This shift can be measured using a double-resonance method, and it can be enhanced by two or three orders of magnitude by partially saturating the CESR. It provides a sensitive probe for the detection of nuclear magnetic resonance. Here we report on our measurements of the ¹³C induced Overhauser shift in the systems mentioned above. By means of a lineshape analysis of the ¹³C resonance curves, we investigated the distribution of the conduction electrons over these molecular systems.