Electronic structure and spectroscopic properties of (2S,3S)-2,3-diphenyl-5,6-diheteroaryl-2,3-dihydropyrazines and their model oligomers

The synthesis, chemical and spectroscopic characterization of four novel (2S,3S)-2,3-diphenyl-5,6-diheteroaryl-2,3-dihydropyrazines containing pyridine (DPPn2), pyrrole (DPPy2), thiophene (DPTh2) and furan (DPFu2) units were presented. The experimental absorption spectra in methanol exhibit very broad lowest energy band with the maximum ranged from 307 nm for DPFu2 to 443 nm for DPPn2. The most intense fluorescence was observed for the molecules containing the pyrrole heterocycles in dichloromethane. The role of the (2S,3S)-2,3-diphenyl-2,3-dihydropyrazine as the spectroscopic or electrochemical active central building block was also estimated theoretically for the series of symmetric V-shaped model molecules containing two hexamer oligomers. In this context, the quantum chemical calculations were used for the investigation of the molecular electronic structure, ionisation potentials, electron affinities and molecular orbital energy diagrams of neutral and charged states. The calculations of the B3LYP-D(COSMO) pair-interaction energies for two model clusters of DPPy2(CH3OH)2 and DPPy2(CH2Cl2)2 indicated the possible formation of the hydrogen bonds between the solvent molecules and nitrogen atoms of central 2,3-dihydropyrazine and pyrrole units.