We report the synthesis and characterization of a series of isomeric indacenodithiophenes ( iso -IDTs) bearing various ethynyl substituents at the apical carbons. Absorption spectroscopy, cyclic voltammetry, and density functional theory (DFT) calculations were performed to investigate the electronic properties of these compounds. Notably, analogues with reduced steric protection (i.e., trimethylsilyl, adamantyl) were also successfully isolated and investigated. Computed nucleus-independent chemical shifts and ring current plot analyses reveal that iso -IDTs display reduced antiaromatic character compared to indenofluorene (IF) and the previously reported syn- and anti- fused IDT isomers, suggesting that the π-bond arrangement within the indacenodithiophene π-system can be leveraged for tuning their optoelectronic properties.
Meegasmullage et al. (Sun,) studied this question.