Structural and electronic properties of poly(thiaheterohelicene)s

Quantum chemical methods have been applied on model oligomers of poly(thiaheterohelicene)s to investigate the structural and electronic properties of these systems. Specifically, the properties of the helical structures found for poly(heterohelicene) and poly(methyl-sulfonium), which were calculated using density functional theory calculations, are in good agreement with available experimental data. The geometrical parameters obtained for poly(methyl-sulfonium) reflect the enlargement of the inner carbon-carbon bond lengths at the thiophene rings, which are those closer to the helical screw axes, and lead to reduce their aromaticity of such heterocycles. On this basis, a relationship between the aromaticity and the lowest π-π* transition energy has been established. Finally, the lowest π-π* transitions have been extrapolated for infinite polymer chains of poly(heterohelicene) and poly(methyl-sulfonium) using different theoretical approaches