Photophysics and photodynamics of Pyronin Y in n-alcohols

The photophysical properties and photodynamics of Pyronin Y (PyY) dye compound in seven polar protic solvents (n-alcohols) were examined as a function of temperature by using UV-visible, steady-state and time-resolved fluorescence spectroscopy techniques. To understand dye-solvent interactions, photophysical parameters including Stokes' shifts, fluorescence quantum yields and fluorescence lifetimes were determined. To examine the effect of solvent polarity, the difference between the ground state dipole moment and the excited state dipole moment was determined. For this purpose, the multiple regression analysis and the Kamlet-Taft technique were used. Moreover, photodynamic parameters, rotational relaxation times and steady-state anisotropy were calculated. The result showed that the specific interactions of PyY with the solvent molecules take place through hydrogen bonding. As the hydrocarbon chain of the alcohols gets longer, photophysical parameters diminish, probably because of weaker hydrogen bonding. Furthermore, it was found out that the dipole moment of excited states (μ_e ) is higher than that of the ground state (μ_g ). In addition, Brownian motions increased with the increasing temperature that weakened the fluorescence character of PyY. It was also revealed that the rotation of PyY increased with a prolonged hydrocarbon chain of alcohol series, due to the lesser extent of hydrogen bonding.