Relationship of Electron Spin Resonance and Semiconduction in Phthalocyanines

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Abstract
The electron mobility of charge carriers in copper phthalocyanine has been determined to be approximately two orders of magnitude greater than that in metal‐free phthalocyanine. This difference can be interpreted in terms of the electron spin resonance results and the intermolecular copper‐nitrogen overlap. The electron spin resonance of copper phthalocyanine magnetically diluted in metal‐free phthalocyanine has been measured in single crystals. The hyperfine structure of the nitrogen ligands, as well as that of the copper hyperfine structure, is clearly resolved. An analysis of the data in terms of molecular orbitals suggests a scheme of strong out‐of‐plane π bonding with the π orbitals of the phthalocyanine ring and almost no in‐plane π bonding. This brings about an inversion of the usual positions of the copper Eg and B2g orbitals. This strong π bonding predicts that in metallo‐organic compounds of this type, the organic π‐electron delocalization is increased to include the central metal atom, and properties dependent on this delocalization should be altered when copper is used. The increased delocalization of the π‐electron orbitals gives rise to larger intermolecular π wavefunction overlap resulting in a greater mobility for charge carriers in copper phthalocyanine.

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