The interaction of light with biomolecules is an important aspect of our everyday lives. Several biologically important molecules that depend on light were investigated in the course of this research. The emphasis was on the chemical and physical characterization of these biomolecules and encompassed several fundamental analytical techniques;Photosynthesis is the process by which organisms convert light energy into chemical energy. An important aspect of photosynthesis research has been the investigation of biomimetic systems that will mimic natural photosynthesis. To this end, specifically halogenated chlorins were synthesized and the effect of halogen substitution on the spectroscopic and electrochemical properties was investigated. Raman, absorption, and NMR spectroscopies were utilized in addition to cyclic voltammetry. Optical spectra of the derivatized compounds were similar to those of the parent compounds, while the redox properties were more strongly affected. In addition, further experiments are planned in which these halogenated compounds will be used as intermediates in the synthesis of biomimetic photosynthetic systems;The second section describes the synthesis and characterization of suspected bacteriochlorophyll degradation products. An important concern when working with photosynthetic pigments is the viability of the compounds. In in vivo photosynthetic reaction centers, these pigments are quite stable. However, when removed from their native environment, they are subject to degradation. Knowledge of the conditions under which the least amount of degradation occurs and the nature of the degradation products will assist in the formulation of biomimetic membrane systems;The final sections deal with hypericin, a photodynamic quinone compound. Initial spectroscopic studies were intended to elucidate the spectral profile as well as establish physical, chemical, and biological parameters of this compound. As little spectroscopic work has been reported, model compounds were utilized to assist in spectral assignments. Section IV describes some preliminary results of hypericin-virus complexes utilizing surface enhanced resonance Raman spectroscopy. The location and environment of the hypericin with respect to the virus will be determined.