Design Principles for the Acceptor Units in Donor-Acceptor Conjugated Polymers.

More than 50 different acceptor units from the experimental literature have been modeled, analyzed, and compared by using the computationally extracted data from the density functional theory (DFT) perspective for tetramer structures in the form of (D-B-A-B) (D, donor; A, acceptor; B, bridge) with fixed donor and bridge units. Comparison of dihedral angle between acceptor, donor, and bridge units, bond order, and hyperpolarizability reveals that these three structural properties have a dominant effect on the frontier electronic energy levels of the acceptor units. Systematic investigation of the structural properties has demonstrated the band gap energy dependency of the acceptor units on the planarity, conjugation, and the electron delocalization. Substitution effect, morphological alternation, and insertion of π-electron deficient atoms in A unit have also an important role to determine physical properties of the donor-acceptor conjugated polymers. This benchmark study will be beneficial for the band gap engineering and molecular design of the donor-acceptor copolymers using different acceptor units for the organic electronic applications.