π‑Electron
Conjugation in Two Dimensions
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Abstract
Organic
oligomers and polymers with extended π-conjugation
are the fundamental building blocks of organic electronic devices.
Novel routes are being explored to create tailor-made organic materials,
and recent progress in organic chemistry and surface chemistry has
led to the synthesis of planar 2D polymers. Here we show how extending
π-conjugation in the second dimension leads to novel materials
with HOMO–LUMO gaps smaller than in 1D polymers built from
the same parent molecular repeat unit. Density functional theory calculations
on <i>experimentally realized</i> 2D polymers grant insight
into HOMO–LUMO gap contraction with increasing oligomer size
and show fundamental differences between 1D and 2D “band gap
engineering”. We discuss how the effects of cross-conjugation
and dihedral twists affect the electronic gaps