Tetraoctylthio- and tetraoctyloxy-substituted lead phthalocyanines: Synthesis, characterization, liquid-crystalline properties, and thin film studies

Peripherally and nonperipherally tetrakisoctylthio- and tetrakisoctyloxy-substituted lead(II) phthalocyanines (PbPcs) were synthesized and characterized using elemental analysis, nuclear magnetic resonance, ultra violet-visible (UV-Vis), infrared (IR), and mass spectroscopies. The mesogenic properties of PbPcs were studied by differential scanning calorimetry, polarized optical microscopy, and x-ray diffraction. The effects of the substitution position and nature of linkage heteroatom on the liquid-crystalline properties and the orientation of the molecules were also studied. Visible absorption spectroscopy yielded an evidence of a thermally induced molecular reorganization in the films. Reflection-absorption IR spectroscopy was used to study the preferential orientation of molecules relative to the substrate surface. The intense bands in the IR spectra of the PbPcs were assigned with the aid of quantum chemical (density functional theory) computations.