Synthesis, structures, and density functional theory computational study of thiophene-containing and fluorodecorated imine-linked polymers

A new series of extended-conjugated and thermally stable thiophene-containing imine-linked polymers were synthesized via a Schiff-base condensation reaction between aryl aldehydes and 2,6-diaminopyridine building blocks. The backbones of the polymers were functionalized with phenyl, fluorosubstituted phenyl, thienyl, and pyridyl aromatic rings. The successful synthesis was confirmed with spectrochemical characterization techniques, including IR, H-1-NMR, C-13-NMR, and elemental analyses. The electronic properties of the polymers were investigated with ultraviolet-visible (UV-vis) absorption spectroscopy; the properties were collected experimentally and calculated with density functional theory (DFT) in the gas phase. The maximum absorption calculated from DFT was higher than the experimental values by about 60 nm; this was attributed to the absence of the solvent effect in the DFT case. The frontier molecular orbital ((HOMO) highest occupied molecular orbital and (LUMO) lowest unoccupied molecular orbital), optical band gap (E-g), and total energy (E-T) values of the optimized structures were calculated. Apparently, there was a significant relation between the number of thiophene rings and the resulting E-g and E-T values. As the number of thiophene rings in the polymer chain increased, E-g and E-T decreased, and the thermal stability of the polymers increased. E-g and the absorption band edges were determined experimentally from the UV-vis and transmittance spectra, respectively. Poly(terthienyl-azomethine-pyridine-azomethine), with the highest thiophene content, had the lowest experimental and calculated E-g values (2.10 and 2.63 eV, respectively). In contrast, upon fluorination, poly[(2,5-dithienyl-1,4-difluorobenzene)-azomethine-pyridine-azomethine] exhibited the highest E-g (2.81 eV) and absorption band edges (2.94 eV), whereas the thermal stability decreased to 250 degrees C. (C) 2016 Wiley Periodicals, Inc.