Stability Due to Peripheral Halogenation in Phthalocyanine Complexes

Abstract

The effect of peripheral halogenation is examined based on analytical transmission electron microscopy and thermal analyses of two chemical family structures, specifically the vanadyl-phthalocyanine family (VOPcX: X = H16, F14.5) and the copper-phthalocyanine family (CuPcX: X = H16, F16, Cl16, Cl8Br8), focusing on the process of molecular changes and crystalline disintegrations. To clarify the molecular transformations, electron energy-loss spectroscopy (EELS) is applied to two fluorinated phthalocyanines (VOPcF14.5 and CuPcF16), by monitoring mass changes as well as energy loss near edge structures (ELNES). The elemental mass of both VOPcF14.5 and CuPcF16 remain constant up to 0.5 C·cm−2, except in the case of mass reduction attributed to oxygen loss occurring in VOPcF14.5. It is expected that the released oxygen will induce higher radiation damage in VOPcF14.5. Although mass variation is not observed in CuPcF16, it is found from ELNES that the π resonant system of nitrogen is more radiation sensitive than that of carbon. These results imply that the electron sensitivity in VOPcX is triggered by eliminated oxygen or, thus, an induced larger empty space, whereas the sensitivity of CuPcX is dominated only by a large intermolecular empty space resulting in the following bond alterations. It is also found that the decomposition temperature (Td) measured by thermal analyses and the characteristic dose (D1/e) are exponentially correlated to the “effective molecular occupancy” (Oe) evaluated as a volume function of molecules in unit cells. By measuring Td and/or Oe, we discuss the durability of peripheral halogenation with respect to the radiation damage.