The time scale for the relaxation of an electronically excited molecule to its ground state in a solvent environment typically ranges from picoseconds 10^-12 seconds to nanoseconds 10^-9 seconds . This process, known as non-radiative relaxation, can occur through various mechanisms such as internal conversion, intersystem crossing, and solvation dynamics.Ab initio calculations, which are based on quantum mechanics and do not rely on empirical data, can be used to predict the relaxation time of an electronically excited molecule. However, the reliability of these predictions depends on several factors, including the level of theory used, the size of the basis set, and the accuracy of the solvent model.In general, higher levels of theory and larger basis sets provide more accurate results but are computationally more expensive. Additionally, the choice of solvent model can significantly impact the predicted relaxation time, as it needs to accurately describe the interactions between the solute and solvent molecules.In recent years, advances in computational methods and hardware have improved the reliability of ab initio calculations for predicting relaxation times. However, it is still essential to validate these predictions with experimental data to ensure their accuracy.