Insight into the electron delocalization in phenylacetylenes and phenylvinylenes: An NBO analysis

Abstract

NBO analysis has been carried out for model molecules to elucidate the delocalization energies in phenylacetylenes and phenylvinylenes (which make up cruciform molecules). The model molecules considered are 1,2- , 1,3- and 1,4- positional isomers of bis(phenylethynyl)benzene, phenylethenyl-phenylethynylbenzene and bis(phenylethenyl)benzene which represent the bent-, cross- and linear-conjugation path ways respectively. The geometry has been obtained at B3LYP/6-311G(d,p) level and the NBO analysis carried out at the same level. It is observed that the substitution of donor and acceptor groups reduces the difference in delocalization energies between these isomers.