Threshold concentration in nonlinear absorbance law
A new nonlinear relationship of the absorption coefficient with the concentration was proposed, allowing calculating the threshold concentration, after which there is a deviation from the Beer-Lambert law. The nonlinear model was successfully tested on a stable dimeric phthalocyanine ligand of J-type in solvents with different polarity. It was shown that deviation from the linearity is associated with a specific association of the macrocyclic molecules, which, in the case of non-polar solvents, leads to the formation of H-aggregates from J-type dimeric molecules. The aggregation number was estimated to be less than 1.5 that has allowed us conducting a series of analytic experiments in a wide range of concentrations (1×10-6 – 5×10-4 mol L-1).