Reversible excited-state transient solvation in binary supercritical fluids revealed by multifrequency phase and modulation fluorescence

Frequency-domain fluorescence spectroscopy is used to study the transient solvation of 4-amino-N-methylphthalimide (4AMP) in binary supercritical fluids composed of 2-propanol and CO₂. The time-resolved emission spectra are constructed for this system with the use of the wavelength-dependent frequency-domain data. Analysis of the experimental data indicates that: (1) 4AMP is pre-associated with 2-propanol prior to excitation; (2) the 2-propanol-induced spectral relaxation occurs on a nanosecond time scale; and (3) the excited-state reaction between 4AMP and 2-propanol is reversible.