Conjugated polymers and aromaticity

A review of the effect of system size on aromaticity via the geometric bond alternation parameter, δ, and the energy gap associated with this distortion from uniform bond distances is presented. Numerous calculations for linear chain aromatic and conjugated polymers are covered with particular emphasis on the role of nonlocal exchange, which enhances both bond alternation and band gap. Design principles for small band gap conjugated polymers are reviewed. The role of bond alternation with respect to structure and gap is emphasized. Aspects of band gap engineering and the critical evaluation of widely used computational methods for polymer properties are also discussed.