Quantum Chemical Investigation Of Ground And Excited States Of Synthetic Analogs Of Anthocyanins

The work presented in this thesis is about the theoretical study on 7-Hydroxyflavylium cation and its clusters with different numbers of water,more precisely,we used quantum chemical methods in order to investigate the structural modifications of our system.Hydroxyflavylium ions are the basic chromophoric unit of anthocyanins and anthocyanidins,the water-soluble pigments that are responsible for the colors of many flowers and 27 families of food plants(giving them their red,mauve or blue colors).In particular,anthocyanidins are derivatives of the 2-phenylchromenylium cation,also known as the flavylium cation.An investigation of the excited state energies and spectroscopic states of the 7-hydroxyflavylium cation in the presence of water as the polar solvent is investigated in this research.Different structures of7 hydroxy flavylium(7-HF)cation were studied as following:(i)the cation alone;(ii)the neutral conjugate base form cation;(iii)the 7-HF cation hydrogen bonded to one discrete water molecule;(iv)the 7-HF cation interacting with a group of 3 discrete water molecules(v)the 7-HF cation interacting with a group of 5 discrete water molecules,respectively.The goal was to describe theoretically the photo dissociation of the 7-hydroxyflavyium cation(7-HF),the major chromophoric moiety of anthocyanin natural plant pigments.TD-DFT with the B3-LYP functional and def2-TZVP basis set including Grimme's D3 dispersion correction proved to be an efficient approach to analyze the excited state proton transfer(ESPT)process in 7-HF.As already mentioned above the solvent effect was modeled by the explicit inclusion of discrete water molecules combining hydrogen-bonding of the photoacid to a cluster by means of the conductor like screening model(COSMO).Pyrano flavylium cations are of importance as artificial analogs of the chromophoric moiety of Pyranoanthocyanins.The latter are dyed molecules that are made from grape anthocyanins during the development of red wines.Looking at confirming the enhanced acidity of the pyrano flavylium cations,B3-LYP/def2-TZVP approach was taken to estimate the pK_a of the methyl group of 4-methylflavylium cations(confronted with experimental data where available).