This thesis investigates the excited states properties within the framework of Frozen Density Embedding Theory (FDET), covering vertical excitation energy (one-photon absorption properties) and extending to two-photon absorption properties. Efforts are made to improve the accuracy of vertical excitation energy by examining the impact of state-specific polarisation from the environment. While achieving a small error in vertical excitation energy, the reliability of the utilized approximations in FDET is evaluated for the two-photon absorption cross section. The computational challenges associated with modeling this property are highlighted. Additionally, the importance of various environment-induced effects is addressed. Last but not least, the oscillation of the entangled two-photon absorption cross section, with time-frequency-entangled pairs, is explored with varying coherence time, and its relationship with the electronic structure of molecules is discussed.