Theoretical Studies on Solvent Effects and Intermolecular Interactions of Organic π-Conjugated Ligand in Solutions

The influence of solvent polarity on the molecular geometries and electronic structures of organic pi-conjugated ligand, N,N'-bis-(3-pyridyl) ethylene-bis-urea(BPEBU), was theoretically investigated within the framework of the polarized continuum model(PCM) via the density functional theory(DFT) calculations. The solute-solvent intermolecular interactions of BPEBU in acetone and ethanol solutions were studied by adopting the discrete solvent model through molecular dynamics(MD) simulations. It is demonstrated that C = O and N-H bonds in urea moiety group and C-N bonds in pyridine rings of BPEBU are polarized and lengthened with increasing the solvent polarity through DFT calculations. Correspondingly, the magnitudes of negative charges of oxygen atoms and positive charges of hydrogen atoms in urea group are increased significantly. The MD simulations show the specific O center dot center dot center dot H-O, N center dot center dot center dot H-O and N-H center dot center dot center dot O hydrogen bonding interactions between BPEBU and ethanol solvents. Only N center dot center dot center dot H-O hydrogen bonds are formed in acetone solutions. And the N center dot center dot center dot H-O intermolecular interaction in acetone solution is weaker than that in ethanol solution. Furthermore, the solute-solvent hydrogen-bonded trimers are optimized by adopting the combined discrete/continuum solvation model through DFT method. The structures of trimers are qualitatively agreement with supramolecular clusters in the first solvation shell from molecular dynamics simulations.