FLUORESCENCE EMISSION AND ANISOTROPY FROM RHODAMINE DIMERS

The absorption, fluorescence emission, and excitation fluorescence ani sotropy spectra of a rhodamine dye in a water-glycerol solution at hig h concentration were investigated to determine spectroscopic propertie s of the ground state dimer. The combination of data from these spectr a measured at several dye concentrations contained sufficient constrai nts on the model for dimer association to permit an estimate of: the a ssociation constant, the extinction coefficients, the relative fluores cence quantum yield, and the emission spectra of the monomeric and dim eric species. The rhodamine dimer is an efficient fluorescence emitter with fluorescence anisotropy equivalent to that of the pure monomeric species over the range of excitation wavelengths covering its two low est energy transitions.