Perturbation of hydrogen bonding in hydrated pyrrole-2-carboxaldehyde complexes.

The interaction of external water molecules with hydrated pyrrole-2-carboxaldehyde PCL/(H2 O)n complexes was investigated. The work was supported by both theoretical [DFT/TD-DFT methods using 6-311G++(d,p) basis set in the ground (S0 ) and excited (S1 , S2 , S3 )states] and experimental [UV-Vis, FTIR and Raman] verification. The focus of the present work was on the weak intermolecular O-H⋯O, N-H⋯O-H hydrogen bonded interaction (Ier HB) between PCL and external water molecules, and the influence of increasing the number of water molecules to form hydrated PCL/(H2 O)n complexes. Effects were observed on different vibrational normal modes and on electronic transition levels. A hydrogen-bonded network of water induces a shift to higher energy in certain normal modes of PCL to form stable PCL/(H2 O)n complexes by lowering the barrier energy. Potential energy distribution (PED) analysis indicates a significant charge transfer from PCL to water by creating a water bridge. Hydrogen bonding effects account for the substantial red shift and broadness in νNH , νCO vibrational modes. Water rearrangement turns out to be the main driving force for hydrated complex formation. Graphical abstract Stability of PCL/(H2 O)4 hydarted complex.