The project centres on the aromaticity concept applied to excited states of organic molecules. Quantum chemical calculations, using DFT/TD-DFT as well as complete active space and coupled cluster methods, will be applied. In the lowest pipi* singlet and triplet excited states, the (anti)aromaticity of a cyclic system is governed by Baird's rule, stating that compounds with 4n pi-electrons become aromatic, whereas 4n+2 species become antiaromatic. Through this project, calculations will be used to investigate the impact of excited state aromaticity and antiaromaticity on the photochemical reactivity of heteroaromatic systems and other aromatic compounds that are more complex than simple annulenes.