Magnetic properties of lithium phthalocyanine

The magnetic susceptibility and specific heat of the organic semiconductor lithium phthalocyanine (LiPc) are studied for temperatures 1.5 K ≤ T ≤ 300 K. LiPc has one unpaired electron on the inner ring of the macrocycle. These electrons are localized along the molecular stack and behave like spin chains. The spin susceptibility, as determined by electron spin resonance measurements, and the magnetic contribution to the heat capacity are well described by a model of a S = 1/2 antiferromagnetic Heisenberg chain. The exchange constant is given by J ≈ 40 K. In comparison the iodinated compound LiPcI is ESR silent. Due to oxidizing with iodine the unpaired electrons have been removed from the macrocycle.