Vibrationally resolved absorption emission resonance Raman and photoelectron spectra of selected organic molecules associated radicals and cations : a time dependent approach Time dependent correlation function based methods to study optical spectroscopy involving electronic transitions can be traced back to the work of Heller and coworkers. This intuitive methodology can be expected to be computationally efficient and is applied in the current work to study the vibronic absorption emission and resonance Raman spectra of selected organic molecules. Besides the non standard application of this approach to photoionization processes is also explored. The application section consists of four chapters as described below. In Chapter 4 the molar absorptivities and vibronic absorption emission spectra of perylene and several of its N substituted derivatives are investigated. By systematically varying the number and position of N atoms it is shown that the presence of nitrogen heteroatoms has a negligible effect on the molecular structure and geometric distortions upon electronic transitions while spectral properties are more sensitive: In particular the number of N atoms is important while their position is less decisive. Thus N substitution can be used to fine tune the optical properties of perylene based molecules. ...