Quantifying Planarity in the Design of Organic Electronic Materials

Abstract Planarity is essential for many organic electronic materials as it maximizes the intramolecular π‐orbital overlap and enables efficient intermolecular interactions through π‐stacking. We propose a statistical way of quantifying the planarity of a wide range of conjugated systems. The quantification takes into account all torsional conformations and their relative contribution to the overall structural disorder, through a planarity index ⟨cos 2 ϕ ⟩. The propensity for planarization and the effect of rotational disorder were examined for a series of commonly used building blocks. The application of the analysis to extended conjugated systems and the correlations between the gas‐phase ⟨cos 2 ϕ ⟩ and crystallographically observed planarity in the solid state were explored. Our calculations also reveal a previously unrecognized effect of increasing band gap upon planarization for conjugated systems coupling strong electron donor and acceptor units.