Effect of Sterically Protective Groups on the Aromaticity of Fully Unsaturated Oligoquinanes

Oligoquinane derivatives have unique aromatic properties, which dictate the stability of the molecules and their potential applications in various devices. Due to the challenge in their synthesis, systematic studies of these molecules are still lacking. In this work, we perform density function theory and nucleus-independent chemical shift (NICS) calculations on 24 oligoquinane derivatives that are composed of two, four, five, and six five-membered rings. Pentaquinane without any protection groups was predicted to be aromatic and stable. It would be interesting to synthesize the molecule and carry out further electronic and optical measurements. Among introducing various protection groups to the bare oligoquinanes, single bond protection was found to be the least effective in the change of aromaticity of oligoquinane. In the protection of benzene rings, aromaticity change depends on the configuration of the molecule formed. HOMO-LUMO energy gap and UV-Vis absorption also depends on the molecular shape. The results show the potential application of the oligoquinanes as they can be diversely tuned for specific applications, and therefore is worthy of future studies.