Synthesis, structural analysis, spectrophotometric measurements and semiconducting properties of 3-phenyl azo-4-hydroxycoumarin thin films

Abstract

3-phenyl azo-4-hydroxycoumarin, PAHC, compound was synthesized by reacting aniline diazonium salt with 4-hydroxy coumarin. The thin films of PAHC were prepared on the glass and quartz substrates by thermal evaporation technique under vacuum pressure 10-5 mbar. The structure of thin films was characterized using X-ray diffraction, XRD, and Fourier transformation infrared, FTIR, techniques. The XRD pattern for the pristine PAHC thin film showed nanocrystallites distributed in amorphous matrix. Annealing at 423 K improved the crystallinity of films and the crystallite size is in the range 23-36 nm. FTIR showed different vibrational modes, observed in infrared spectra of the powder, pristine and annealed thin films, were assigned to the molecular bonding structure of PAHC compound. The optical properties of PAHC thin films were investigated by the spectrophotometer measurements of the pristine and annealed PAHC films in the range 200-2100 nm. The refractive and absorption indices of the pristine and annealed PAHC films were calculated from measured transmittance and reflectance data. The results showed that the refractive and absorption indices of thin films are influenced with increasing annealing temperature. The direct allowed transitions were the most probable transition and the optical band gap was found to vary from 2.14 to 2.21 eV with increasing annealing temperature. The single oscillator model was applied in the normal region of dispersion spectrum to determine the dispersion parameters and it is noted that they are decreased with annealing temperature. The AC electrical conductivity, σAC, and the real and imaginary parts of dielectric constants measurements were investigated in temperature range 304-413 K and frequency range 0.1-100 kHz; they confirmed semiconductor behavior of the PAHC films.