A THEORETICAL INVESTIGATION OF THE ELECTRONIC-PROPERTIES AND STRUCTURE OF SOME MODEL POLY(DIACETYLENES)

The electronic properties of some model poly(diacetylenes) were investigated by using AM1 and, to a limited extent, MNDO and PM3 semiempirical SCF-MO methods. The capped-bond option allowed for simulation of polymer structures but the option has limitations when computing electronic properties of conjugated polymers. With optimized geometries, AM1-computed structures for poly(diacetylene) models favor the enyne structure. The chemical and electronic effects of substituents on the structure of the polymer backbone were investigated, and the Koopman ionization potential and bandgap were computed and discussed. The changes in HOMO and LUMO energies as a function of nonplanarity along the backbone were also calculated. The bandgaps of some diacetylene monomers and several oligomers were computed for comparison with experimental values of diacetylene monomers and polymers. Finally, some AM1 calculations are included showing variations in geometry, atomic charge, and bandgap with chain length in a series of oligomeric diacetylenes.