IR Spectroscopy and ab initio calculations of imidazophenazine and its derivatives in a low-temperature argon matrix

Abstract

IR Spectroscopy is used for the first time to study the absorption spectra (400–1700cm−1 range) of imidazo-[4,5-d]-phenazine (F1) and its derivatives 2-methylamidazo-[4,5-d]-phenazine (F2), 2-fluorodimethylimidazo-[4,5-d]-phenazine (F3), and 1,2,3-triazolo-[4,5-d]-phenazine (F4) in a low-temperature argon matrix (10K). The spectra of these compounds are analyzed using computed frequencies and intensities of harmonic vibrations obtained by the quantum-mechanical DFT method (B3LYP∕6-31++G** and M05-2X∕6-31++G**). The low-temperature IR spectra of the compounds F1–F4 are in good agreement with the computed spectra. The spectra obtained contain bands which are common to all compounds F1–F4 as well as bands which are characteristic to each individual compound. The strongest transformations in the IR spectra of the F2–F4 compounds relative to the F1 spectrum are observed for the compound F4 where they are due to the substitution of a nitrogen atom for a carbon atom in the imidazole ring. A comparative analysis of the spectra of the isolated molecules with the spectra of polycrystalline samples in KBr pellets is performed. The structures, interaction energies, and the harmonic frequencies and their intensities are calculated for hydrogen-bonded and stack dimers of these compounds. The computed dimer spectra describe well the IR spectra of the compounds F1–F4 in KBr pellets.