Interaction energy in pairs of phthalazinium dibenzoylmethylid (PDBM)-protic solvent molecules estimated in the limits of the cell ternary solution model, by spectral means.

The dipolar compound Phthalazinium-dibenzoylmethylid (PDBM) was used as spectrally active molecule in order to analyze the molecular interactions in ternary solutions containing at least one protic solvent. In PDBM+protic solvent (1)+aprotic solvent (2) ternary solutions, PDBM can be involved both in universal and specific interactions reflected in solvatochromic effects. The protic solvent (or the solvent with the higher electric permittivity) was considered as being active from the interactions point of view. The content of the first solvation sphere of the studied ylid has been established on the basis of the statistical cell model of ternary solutions. The active solvent molecules are dominant in the first solvation sphere of the PDBM molecules. The difference between the interaction energies in the PDBM-active solvent (1) and PDBM-inactive solvent (2) molecular pairs has been determined for three binary solvents water+ethanol (W+E), propionic acid+chloroform (PA+C) and octanol+1,2 dichloroethane (O+DCE). The hydrogen bond formation energy of the PDBM-protic solvent complex has been estimated in the binary solvents PA+C and O+DCE containing one protic (PA and O, respectively) and one aprotic solvent with close electro-optical parameters refractive index and electric permittivity of the components.