A Quantitative Study of the Changes Produced in the Absorption Bands of Certain Organic Fluorescent Dye Solutions by Alterations of Concentration and Temperature

Abstract

The forms of the absorption bands have been obtained for solutions of rhodamin-B and eosin at different concentrations and temperatures; also for solutions of fluorescein, uranine, and resorcinol-benzein at various temperatures. It has been found that an increase in concentration produces the same general effect on the absorption bands as a lowering of the temperature of the solutions. In a concentrated aqueous solution of rhodamin-B there are two prominent bands in the visible which overlap. Change in concentration produces unsymmetrical modifications in the forms of the bands, one band growing at the expense of the other. Increase in the temperature of the concentrated solution produces the same effect on the bands as a reduction in concentration. Temperature changes produce only a slight effect on the absorption of a dilute solution. Increase in concentration of an alcoholic solution of rhodamin-B produces an increase in the absorption per molecule and a shift of the bands towards the red. Lowering the temperature of a dilute solution produces an effect similar to that due to an increase in concentration. Decrease in temperature of a concentrated solution produces an increase in absorption which is less than for a dilute solution, and produces no observable shift in the bands. Increase in concentration of an alkaline alcoholic solution of eosin produces a slight increase in absorption, and a shift of the bands towards the violet. Decrease in temperature produces a similar effect which is more marked for a dilute solution than for a concentrated solution. Increase in temperature in neutral alcoholic solutions of fluorescein and eosin causes a marked increase in the absorption, but no shift of the bands. The solutions become colorless at very low temperatures. Increase in temperature of an alcoholic solution of uranine produces an increase in the intensity of the band, and a shift of the band towards the red. Increase in temperature in alcoholic solutions of resorcinol-benzein causes a decrease in absorption with no appreciable shift of the bands.A theory recently proposed by Merritt to account for the form of the absorption bands of the organic dye solutions on the long wave-length side has been tested with the data herein recorded and has been verified for dilute aqueous solutions of rhodamin but not for the other solutions.