Effect of microwave irradiation time and temperature on the spectroscopic and morphological properties of nanostructured poly(carbazole) synthesized within bentonite clay galleries

Abstract

Microwave irradiation has been widely used in the synthesis of organic, inorganic, and inorganic–organic hybrid materials because of its well known advantages over conventional synthetic routes. Polycarbazole (PCz) is a hole transporting conducting polymer and by virtue of this property is attracting considerable attention for its application in organic light emitting diodes (OLEDs) and solar cells. For advanced technologies, PCz of controlled morphology, nano dimension, and higher optoelectronic properties is desired. These objectives are achievable through using innovative synthetic routes. Towards this end, we have attempted to synthesize PCz under solid state conditions in the confined environment of the interlayer space of bentonite clay through microwave irradiation with ammonium persulphate as initiator. The effect of time and temperature of microwave irradiation on the shape, size, molar mass, UV-vis and fluorescence characteristics of PCz and PCz–clay nanohybrids have been thoroughly investigated and interpreted. The temperature of the microwave irradiation was from 30 to 50 °C and the time was varied from 2 to 6 min. The effects of both temperature and time of microwave irradiation on the synthesized nanocomposite was investigated by FT-IR, UV, XRD techniques. PCz extracted from clay galleries exhibited a spherical shape under all synthesis conditions. The size of spheres, in the nanosize domain, was found to be dependent upon the temperature and time of microwave irradiation. UV-vis spectral analysis showed that microwave irradiation produced a polaronic state in PCz like cyclic voltammetry (CV). Oscillator strength of the polaronic transition was noticeably enhanced with temperature and time of microwave irradiation. FT-IR analysis revealed that PCz formed spiral shaped particles within clay galleries. Time and temperature of microwave irradiation was found to significantly enhance the fluorescence intensity of PCz–bentonite nanocomposites; thus the HOMO and LUMO orbitals of PCz are favorably perturbed by microwave irradiation in a significant measure. Enhancement of optoelectronic parameters of microwave synthesized PCz is expected to drastically improve the quantum efficiency of OLEDs and power efficiency of organic solar cells.