A novel oligo-pyrazole-based thin film: synthesis, characterization, optical and morphological properties

Pyrazole-3,4-dicarboxylic acid 2 was synthesized via the hydrolysis of pyrazole-3-carboxylic acid 1 and subsequently heated with thionyl chloride to give the novel pyrazole-3,4-dicarbonyl dichloride 3, which was easily converted into oligo-pyrazole 4 upon its reaction with p-phenylene-diamine. These newly synthesized compounds were characterized by ¹H-NMR, ¹³C-NMR, and FT-IR spectroscopy, and gel permission chromatography (GPC). Three novel oligo-pyrazole thin films were prepared using oligo-pyrazole 4 with these respective values of thickness: 20, 21, and 24 μm. The optical properties of the films, including the absorbance, transmittance, and optical band gap, were determined using UV-vis spectroscopy. The E values of the films were found to be 1.426, 1.537, and 1.648 eV for the 20, 21, and 24 μm thick organic films, respectively. Atomic force microscopy (AFM) was used to examine the surface morphology and properties of the organic films. In the AFM images, a few black regions were observed and several yellow regions appeared over a large area, and the surface of the oligo-pyrazole films had an extremely low roughness value. The as-synthesized oligo-pyrazole has great potential in optoelectronic applications according to the optical properties of the as-prepared films. Graphical abstract.