THE CORRELATION BETWEEN THE ABSORPTION AND THE FLUORESCENCE ENERGY SPECTRA,AND THE QUANTUM YIELD OF CHLOROPHYLL a IN DIFFERENT SOLVENTS†

Abstract— The applicability of Stepanov's relation to solutions of chlorophyll a in 17 solvents was determined. The value of T* (the local temperature of the excited molecules calculated by the relation) was higher than T (the ambient temperature) in 7 solvents and lower in one. The relative quantum yield determined by comparing the fluorescence spectrum with the thermal emission spectrum was fairly constant (? 1.0) up to 690 nm in dioxane, methylene chloride and dimethylformamide. In other solvents its value at 690 nm varied between 0.2 and 067. It is suggested that existence of a solute-solute or solute-solvent interaction in some solvents could possibly cause such a drop in the quantum yield.