Quantum-Chemical and Solvatochromic analysis of solvent effects on the Electronic Absorption Spectra of Some Benzodiazepine Derivatives

The solvatochromic behaviour of two ketonic derivatives of benzodiazepine namely 7-chloro-1-methyl-5-phenyl-1,5-benzodiazepine-2,4-dione (Clobazam®) and 5,(2-chlorophenyl)-7-nitro-2,3-dihydro-1,4-benzodiazepine-2-one (Clonazepam®) were analysed in some selected solvents of different polarities using UV-Visible spectroscopy and DFT computational techniques. The solute-solvent interactions were evaluated by means of Kamlet-Taft’s Linear Solvation Energy Relationship (LSER) concept. The results show that electronic absorption properties of the compounds depend on the solvent polarity and both specific and non-specific interactions between solute and solvent. Also, the spectral properties show satisfactory correlation with solvatochromic parameters (α, β and π). The plot of ῡmax calculated against ῡmax observed in the representative solvents gives a good linear regression value of R2=0.998.The results of Frontier Orbital calculations showing the differences between HOMO and LUMO of the ground states and various excited states of Clobazam® and Clonazepam® are -5.15eV and -4.20eV respectively and both are in good agreement with the most important transitions observed in the two compounds.