Solvent effects on the steady state photophysics of estrone and 17β-estradiol

Absorption and emission yields for estrone and 17β-estradiol were measured in a variety of room temperature solvents. Molar extinction coefficients were found to not vary as a function of solvent, while fluorescence yields were found to be significantly affected by the polarity and hydrogen-bond accepting ability of the solvent, with the yield for 17β-estradiol being highest in nonpolar, hydrogen-bond donating solvents, and lowest in the nonpolar, hydrogen-bond accepting solvent ethyl acetate. Estrone's emission yield was found to be a factor of ten smaller than 17β-estradiol's. Strong solvent and excitation wavelength dependences were found for the relative amounts of emission between estrone's two emission bands, with increased relative emission occurring in nonpolar aprotic solvents, and under higher excitation energies. These results are interpreted with the aid of vertical excitation energies from time-dependent density functional calculations using both explicit and implicit solvation models.