Short-lived intermediates arising from the donor-acceptor interaction of non-steroidal anti-inflammatory drug (NSAID)-(S)-naproxen (NPX) and its (R)-enantiomer with the tryptophan amino acid residue (Trp) have been studied by spin chemistry and photochemistry methods. The donor-acceptor interaction has caried out in a model linked system-dyad under the UV-irradiation. Interest in the NPX-Trp dyad diastereomers is connected with the possibility of using them as models of ligand-enzyme binding as long as amino acid residues are located at the enzyme's active centers. It is these residues that interact with NSAID during the binding. It is widely thought that charge transfer processes are involved in the process of drug-enzyme binding. Withing this framework the role of charge transfer in NPX-Trp excited state quenching have been investigated. The analysis of the chemically induced dynamic nuclear polarization (CIDNP), as well as fluorescence kinetics and quantum yield in different polarity media has shown that the main channel of NPX fluorescence quenching is the intramolecular electron transfer between NPX and Trp fragments. Electron transfer rate constants and fluorescence quantum yields of diastereomers have demonstrated stereodifferentiation.