Ultrasound-assisted synthesis of fluorescent oligomers of triphenylamine modified polyquinones: A comparison of experimental and computational spectral studies

Abstract

The present study reports polymerization of 9, 10- anthraquinone (AQ) and 1, 4- naphthoquinone (NQ) with triphenylamine (TPA) via ultrasound-assisted method. The oligomers were characterized by nuclear magnetic resonance spectroscopy (1H NMR), fourier transform infrared spectroscopy (FTIR), Uv–vis spectroscopy, X-ray diffraction studies and transmission electron microscopy (TEM) studies. The structural optimization of the oligomers was performed using density functional theory (DFT) with basis set 6–311++G(d,p). The Mulliken atomic charges, HOMO and LUMO calculations, 1H NMR chemical shifts as well as UV-spectra were theoretically computed and compared with the experimental data. XRD studies confirmed the formation of highly crystalline oligomers. The polyquinones upon modification with TPA revealed formation of well-organized chain like structures which was shown by TEM studies. The theoretical as well as experimental IR, 1H NMR as well as UV spectra were observed to be in close agreement with each other. The band gap values were computed to be 4.88 eV, 5.96 eV, 1.53 eV and 1.86 eV for PAQ, PNQ, PAQ/TPA and PNQ/TPA respectively. The TPA modified oligomers exhibited fluorescence emission around 800 nm and the quantum yield (Φ) values were obtained as, 0.23 and 0.33 for PAQ/TPA and PNQ/TPA. Confocal studies revealed intense red emission in case of PAQ/TPA which could be utilized as a photosensitizer in photodynamic therapy.