Synthesis and devices characterization of pyrazolo[4,3-b] pyridine derivatives containing methoxy and hydroxy phenyl groups

Two pyrazolo[4,3-b] pyridine derivatives namely; 2,3-dihydro-6-(4-methoxyphenyl)-1-methyl-3-oxo-2-phenyl-1H-pyrazolo[4,3-b]pyridine-5-carbonitrile (L1) and 2,3-dihydro-6-(4-hydroxyphenyl)-1-methyl-3-oxo-2-phenyl-1H-pyrazolo[4,3-b]pyridine-5-carbonitrile (L2) were prepared. The thermal analysis showed that the L1 is stable up to 266 degrees C, whereas L2 is stable up to 376 degrees C. The L1 and L2 powders were found to have polycrystalline structure in which their lattice parameters and Miller indices were determined. Thin films of L1 and L2 were deposited by thermal evaporation technique. The absorption spectra of the films were measured, from which the optical band gap of L1 and L2 films was estimated as 2.72 and 2.83 eV, respectively. Two devices based on the films of both materials, independently, were deposited onto p-Si single crystal substrates, were fabricated and showed rectification behavior. The current density-voltage (J-V) characteristics of both devices were analyzed in which the diode parameters were determined. The device based on L1 and L2 showed ideality factor of 2.73 and 3.5, respectively. Under illumination condition, the device based on L2 showed photovoltaic properties in which the open circuit voltage and short circuit current were measured as a function of light intensity.