Tuning the spectral, thermal and fluorescent properties of conjugated polymers via random copolymerization of hole transporting monomers

Abstract

With the aim to design conjugated copolymers of hole generating monomers, the present paper reports for the first time, ultrasonic-assisted synthesis of poly(o-phenylenediamine) and polycarbazole using different molar ratios of the two monomers. The copolymerization was established by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, ultraviolet-visible spectroscopy and differential theromogravimetric analysis while the morphology was investigated using X-ray diffraction and transmission electron microscopy studies. The copolymer composition was confirmed by nuclear magnetic resonance spectroscopy which matched with the molar feed ratio. Reactivity ratios (r₁ and r₂ values) confirmed random copolymerization. Infrared spectra revealed that values increased with the increase in the poly(o-phenylenediamine) units. Cyclic voltammetry also confirmed copolymerization. Oxidation and reduction potentials corresponding to the redox peaks of o-phenylenediamine and carbazole copolymers of different composition were close to each other, but fairly different from those of the pure polymers. Redox current densities of copolymers of different compositions were found to vary with the composition. Ultraviolet-visible spectroscopy studies also revealed a progressive change in the optical properties as the copolymer composition changed from 90–10% polycarbazole. X-ray diffraction studies showed morphology of the copolymers to be an intermediate between PCz and POPD where PCz polymer chains appeared least compact and the poly(o-phenylenediamine) chains appeared more close and compact. Fluorescence studies confirmed that as the ratio of poly(o-phenylenediamine) in the copolymer increased from 30–90%, quantum yield increased from 0.27–0.37. Thermogravimetric analysis and differential theromogravimetric studies confirmed copolymerization of the monomers and showed two types of copolymer complexions which were consistent with the experimentally determined copolymerization ratio.