DFT analysis of vibrational spectra of phosphorus-containing dendrons built from cyclotriphosphazene core

FTIR and FT-Raman spectra of phosphorus-containing dendrons built from the hexafunctional cyclotriphosphazene core with five terminal aldehyde (G0′) or P-Cl (G0) groups and one ester function have been recorded and analyzed. The optimized geometry, frequencies and intensity of IR bands of dendrons were obtained by the density functional theory (DFT). It was found that the internal skeleton of G0, G0′ molecules exists in a single stable conformation with slightly non-planar cyclotriphosphazene core. But terminal ester group in G0 molecule may adopt flat and chair rotational isomers. The flat conformer is 0.04 kcal/mol less stable compared to the chair conformer. The bond lengths and bond angles obtained by DFT show the best agreement with experimental data. Relying on DFT calculations a complete assignment of vibrations is proposed for different parts of dendrons. The calculated frequencies and intensity of bands in the IR spectra of dendrons are found to be in reasonable agreement with the experimental results. Our study reveals that the most reactive site in G0 is the PCl2 terminal groups. The local softness of CO bond of benzaldehyde in G0′ is higher than that of methylbenzoate group.