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Abstract
Ab initio molecular electronic structure methods at the HF-SCF and post HF correlated methods at the MP2, MP4 and Coupled clusters (CC) methods and DFT methods, with different extended basis sets, have been used to compute the ground and excited state electronic properties of bio-active molecules. Detailed charge density analysis, molecular topology of charge density and analysis of charge density characteristics along reaction pathways have been performed aiming to correlate these electronic properties to the structural and biological activity of molecules. A direct manifestation of the structural and electronic features of molecules is their electronic spectra. Experimental and TD-DFT theoretical investigation of these electronic spectra enabled a much deeper insight into the structural-activity relationships. Gas phase acidities of several different molecular systems have been computed at high levels of theory. Dynamics of the protonation processes were very closely examined. Reaction profiles have been constructed and various geometric, topological and electronic descriptors have been evaluated, analyzed and discussed. Quantitative analysis of substituent effects, polarizations and hyper polarizabilities and energy gaps were also analyzed and discussed. This work presents also our contribution to applications of the modern computational chemistry tools in different areas of research. Thus, we have investigated the possibility of designing molecular switches and signaling devices based on Schiff bases or naphthol derivatives; a growing and very promising area of research. Furthermore, quantitative structure-activity relationships have been attempt and arrived at for different important class of bio-active molecules