Graph-theoretical parameters for -MO calculation of phenols from DFT-calculated energies: application to charge-transfer complexes

By representing phenols in terms of vertex- and edge-weighted graphs, expressions for the highest-occupied -molecular orbitals of phenols have been derived in terms of the vertex weight hO (for phenolic oxygen) and edge-weight kC-O (for the C-O bond). Graph-theoretical methods have been used to evaluate the quantities involved in such expressions. The HOMO energies of the phenols calculated by density functional theory using the 6-31++G** and 6-311+G(2d,p) basis sets have been correlated with these expressions to estimate the parameters hO and kC-O. The acceptability of the estimated values was tested by their ability to explain the experimentally observed trends in CT transition energies of charge-transfer complexes of phenols with p-chloranil.