  Novel low-band-gap copolymer oligomers are proposed on the basis of density
functional theory (DFT) quantum chemical calculations of photophysical
properties. These molecules have an electron donor-accepter (D-A) architecture
involving poly(3-hexylthiophene-2,5-diyl) (P3HT) as D units and furan, aniline,
or hydroquinone as A units. Structural parameters, electronic properties,
highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital
(LUMO) gaps and molecular orbital densities are predicted. The charge transfer
process between the D unit and the A unit one is supported by analyzing the
optical absorption spectra of the compounds and the localization of the HOMO
and LUMO.
