Eur. Phys. J. B 6, 317-322 (1998)
https://doi.org/10.1007/s100510050555

Magnetic susceptibility, heat capacity, and optical conductivity of LiPc and LiPcI

¹ Institut für Physik, Elektronische Korrelationen und Magnetismus, Experimentalphysik V, Universität Augsburg, 86135 Augsburg, Germany
² Institut für Festkörperphysik, Technische Universität Darmstadt, 64289 Darmstadt, Germany
³ Institut für anorganische Chemie, Christian-Albrechts Universität 24098 Kiel, Germany
⁴ Max-Planck-Institut für Physik komplexer Systeme, 01187 Dresden, Germany

Corresponding author: ^a michael.dumm@physik.uni-augsburg.de

Received: 16 June 1998
Accepted: 14 July 1998
Published online: 15 December 1998

Abstract

The magnetic susceptibility, using dc and electron spin resonance (ESR) methods, the specific heat, and the infrared properties of the one-dimensional molecular semiconductors lithium phthalocyanine (LiPc) and the iodinated compound LiPcI have been investigated for temperatures  K. LiPc has a half-filled conduction band and is expected to be an organic metal. However, due to the strong Coulomb repulsion the system is a one-dimensional Mott-Hubbard insulator with a Hubbard gap of 0.75 eV as inferred from optical measurements. The localized electrons along the molecular stacks behave like a S = 1/2 antiferromagnetic spin chain. The spin susceptibility, as determined by ESR experiments, and the magnetic contribution to the heat capacity show a Bonner-Fisher type of behavior with an exchange constant  K. LiPcI is an intrinsic narrow-gap semiconductor with an optical gap of 0.43 eV. In ESR experiments it is silent, indicating that all the unpaired electrons have been removed from the macrocycle via doping with iodine.