Photophysical, photochemical and liquid-crystalline properties of novel gallium(III) phthalocyanines

The synthesis, liquid crystalline, photophysical and photochemical properties of the peripheral- and non-peripheral-tetra-substituted alkylthio gallium(III) phthalocyanines are reported here for the first time. These novel compounds have been characterized by elemental analysis, UV–Vis, IR and 1H NMR spectroscopy and mass spectrometry. The thermal stabilities of the phthalocyanine compounds have been determined by thermogravimetric analysis. The mesogenic properties of these new materials have been investigated by differential scanning calorimetry, polarized optical microscopy and X-ray diffraction measurements. The investigation of thermotropic behavior showed that all of the new compounds are liquid crystalline over a wide range of temperature. The X-ray diffraction patterns confirm that the phthalocyanines form a hexagonal columnar mesophase. Photophysical (fluorescence and photodegradation quantum yields and fluorescence lifetimes) and photochemical (singlet oxygen quantum yields) properties of these compounds have been investigated in toluene. The fluorescence of the substituted gallium(III) phthalocyanines is effectively quenched by 1,4-benzoquinone.

Research highlights
► Synthesis of tetra-substituted alkylthio gallium(III) phthalocyanines.
► Thermotropic and lyotropic mesophase behaviors.
►  Photophysical and photochemical properties.
► Ground state electronic absorption and fluorescence spectra.