Theoretical insight on model linear oligomers and their ring-fused analogs used in organic electronics

Abstract

Theoretical systematic study compares chemical and electronic structure of six series of linear aromatic oligomers and their ring-fused analogues with various chain length of 5- and 6-membered rings. Chemical structure was described by structural HOMED and one-electron density topology EL aromaticity descriptors. The calculations demonstrated that the diradical electronic ground-state system is energetically preferred for larger six-membered acenes where the electronic structure can be separated into two linear polyene chains. The influence of intermolecular interaction on the aromaticity perturbation in crystals was also analyzed for 20 available X-ray structures. The aromaticity of central ring is lowered for longer molecules in solids. Next, the primary effect of aromatic chain elongation on frontier orbital energies and vertical excitation energies was predicted. The calculated data were correlated with experimental ones and polymer limits on investigated properties were estimated. Quantitative criteria of aromaticity were explored for various linear organic molecules with increasing chain lengths to extrapolate electronic properties at the polymer limit. • Systematic DFT study of linear oligomers and ring-fused analogues. • The aromaticity indices are evaluated. • The structural conditions for diradical system are determined. • Electrochemical band gaps and optical transitions are calculated. • Polymer limits on investigated properties are estimated.