Interpretation of the Near-Infrared Absorption of Magnesium Phthalocyanine Complexes in Terms of Exciton Coupling Effects

Abstract

Magnesium phthalocyanine (MgPc) is a blue pigment whose X-phase is known to exhibit an intense near-IR-absorption. Because of this, MgPc has attracted attention as a material useful for laser printers as well as optical disks based on GaAsAl laser diodes. The near-IR absorption has, therefore, been investigated from the standpoints of exciton coupling effects on the basis of the crystal structure. Two kinds of six-coordinate MgPc complexes were grown from solution and their structures were analyzed: MgPc/(H2O)2·(N-methyl-2-pyrrolidone)2 (crystal 1) and MgPc/(2-methoxyethanol)2 (crystal 2). In both crystals, two oxygen atoms of the solvent molecule are coordinated to the central Mg atom above and below the molecular plane, forming a distorted sp3d2 octahedron. Of these crystals, only crystal 1 exhibits a near-IR absorption whose spectral shape is quite similar to that of the X-phase. In addition, the X-phase is also found to contain two water molecules in the normal ambient atmosphere. The near-IR absorption in both crystal 1 and the X-phase can reasonably be interpreted as arising from exciton coupling effects based on the molecular arrangement of MgPc/(H2O)2.