Chlorophyll a (Chl) in most model systems (monolayers, fluid solvents, adsorbed layers, and polymer films) occurs in three forms: `dry monomers' (isolated from interaction with water), hydrated dimers and oligomers built from such dimers; but in nematic liquid crystal (LC) cell `dry monomers' are predominant. It is a competition between the various paths of deactivation of excited Chl. Excitation energy can be emitted as fluorescence, or delayed luminescence, transferred to other forms of Chl (ET), thermally deactivated or used for photochemical reactions. In order to compare the efficiency of these various paths the following measurements were done and analyzed: absorption, fluorescence, fluorescence excitation, photoacoustic spectra, and lifetime of fluorescence in ps range. There are some important differences between Chl in LC cell and polymer films: Chl in LC cell has a much lower concentration of aggregated forms and the pigment molecules are more uniformly distributed as compared to the Chl in polymer samples. To explain ET in polymer films the fractals model has to be used, whereas mean distances between solvated Chl molecules in LC can be obtained from dye concentration. In order to establish the interaction between Chl a and (beta) -carotene the LC cell with both pigments were also investigated.