Application of computational quantum chemistry to excited state aromaticity
The project concerns the influence of aromaticity in the electronically excited states. I will apply the quantum chemical calculations using density functional theory methods to investigate the influence of excited state aromaticity on the photochemical reactivities of small organic molecules. This project exploits Baird's rule which states that the [4n]annulenes are aromatic whereas [4n+2]annulenes are antiaromatic in their lowest ππ* excited states. The concept of excited state (anti)aromaticity together with quantum chemical calculations can be used for the design of compounds that to various extents act as non-polar aromatic chameleons i.e., compounds which can develop aromaticity in their ground and electronically excited states. These compounds are labelled as aromatic chameleons by my supervisor [J. Am. Chem. Soc. 2004, 126, 13938]. [n]Cycloparaphenylenes, the smaller building block of arm-chair carbon nanotubes are also recognized by us as aromatic chameleonic compounds. The novel aromatic chameleons with low singlet-triplet energy gaps can be designed that can have potential applications in organic electronic materials. Computational calculations are needed to investigate the scope and limitations of aromatic chameleons.