DFT calculation of molecular structure and vibrational spectra of the phosphorus-containing G1′ generation dendrimer with terminal aldehyde groups

The Raman and infrared spectra of the first generation of the phosphorus-containing dendrimer with terminal aldehyde groups have been recorded. The structural optimization and normal mode analysis are performed for phosphorus-containing dendrimer on the basis of the ab initio density functional theory. This calculations gave vibrational frequencies and infrared intensities for the t,g,g- and t,-g,g-conformers of the terminal groups. The t,g,g-conformer is 0.34 kcal/mol less stable compared to t,-g,g-conformer. It is found that the repeated units of dendrimer exists in a single stable conformation with planar OC6H4CHNN(CH3)P fragments. All these observations suggest that steric congestion does not disturb the construction of dendrimers even for the highest generations, and that terminal groups are readily available for further reactions. Relying on DFT calculations a complete vibrational assignment is proposed for different parts of the studied dendrimer. Our study reveals that in the G1′ and G1 dendrimers the most reactive are the terminal groups. IR spectroscopy combined with ab initio DFT computation provides unique detailed information about the structure of the technologically relevant materials, which could not be obtained before with any other technique.