Photophysical and charge transport properties of pyrazolines

Abstract

Pyrazoline, an intense green emitting molecule both in solution and solid state, with extended π-conjugation has been synthesized via simple two-step reactions in high yields. Having the electron rich pyrazoline moiety with good redox behavior, pyrazolines can be potential candidates for charge transport material in organic electronic devices. UV-Visible absorption spectra of pyrazolines exhibit peaks below 400 nm, which is a desired feature for charge transport materials because it avoids interference with donor absorption that falls in the visible to NIR region. Electrochemical and theoretical studies show that the HOMO energy level lies at around −4.8 to 5.2 eV depending on the substituents, which is in fact compatible with the PEDOT:PSS/P3HT and work function of the ITO electrode. The experimental hole transport value, measured using the hole only device and space charge limited current (SCLC) method, was found to be in the range of 10⁻⁵ to 10⁻⁶ cm² V⁻¹ s⁻¹, depending on the substituents. The maximum hole mobility calculated by theoretical methods for the pyrazolines is 0.75 cm² V⁻¹ s⁻¹.