Spectral, Thermal and DC Electrical Conductivity of Charge Transfer Complex Formed Between 5,7-Dimethyl-1-oxo-2-phenyl-1H-pyrazolo [1,2-α]pyrazol-4-ium-3-olate and Iodine

Abstract

Reaction of phenylmalonic acid dihydrazide with 2,4-pentanedione proceeded through a novel rearrangement to give 5,7-dimethyl-1-oxo-2-phenyl-1H-pyrazolo[1,2-α]pyrazol-4-ium-3-olate (DPO). This peculiar structure had a positive charge (cation) localized on the pyrazolium ring and a negative charge localized on the other ring. The intermolecular charge-transfer complexes (CTC) formed between DPO as donor and iodine as an acceptor have been studied spectrophotometrically. Doping was done in two ways: by mixing and chemically using different ratios of I2. The suggested structures of the solid iodine charge-transfer complexes were investigated by several techniques using electronic spectra, FTIR spectroscopy and thermal analysis (TGA and DTA). DC electrical conductivity variation with temperature in the range 300–500 K after annealing for 24 h at 100°C and after doping with different ratios of I2 through the two ways of doping is determined for comparison. The activation energies were calculated and the results were interpreted using the band energy model. DC electrical conductivity of the iodine CTC increased with increasing temperature. The iodine CTC are only one or two orders of magnitude higher in DC electrical conductivity than the undoped material, however the energy gap is very small in addition to its thermal stability which suggests the use of these materials in applications like photovoltaic cells.