Changing the geometry of a molecule can significantly affect its excited state properties, such as energy levels and transition probabilities. This is because the molecular geometry influences the distribution of electrons within the molecule, which in turn affects the electronic structure and the way the molecule interacts with electromagnetic radiation.Quantum chemical calculations, such as time-dependent density functional theory TD-DFT and configuration interaction singles CIS , can be used to predict the excited state properties of molecules. These calculations take into account the molecular geometry and the electronic structure to determine the energy levels and transition probabilities.When the geometry of a molecule changes, several factors can be affected:1. Bond lengths and angles: Changes in bond lengths and angles can alter the distribution of electron density within the molecule. This can lead to changes in the energy levels of the molecular orbitals, which in turn affects the energy required for electronic transitions.2. Conjugation and aromaticity: Changes in molecular geometry can disrupt or enhance the conjugation within the molecule, affecting the stability of the excited states. Aromatic systems, for example, have unique electronic properties due to their delocalized -electron systems, and changes in geometry can affect the aromaticity and thus the excited state properties.3. Steric effects: Changes in molecular geometry can lead to steric effects, where the spatial arrangement of atoms or groups within the molecule can influence the electronic transitions. Steric effects can cause changes in the energy levels and transition probabilities by affecting the overlap of molecular orbitals.4. Intermolecular interactions: Changes in molecular geometry can also affect the way molecules interact with each other, such as through hydrogen bonding, van der Waals forces, or - stacking. These interactions can influence the excited state properties by stabilizing or destabilizing certain electronic states.In summary, changing the geometry of a molecule can have a significant impact on its excited state properties, as it affects the distribution of electrons within the molecule and the way it interacts with electromagnetic radiation. Quantum chemical calculations can be used to predict these properties and help us understand the relationship between molecular geometry and excited state behavior.