Dynamic solvatochromism in solvent mixtures

Solvatochromism and thermochromism of 4-aminophthalimide and 4-amino-N-meth ylphthalimide were studied by absorption and steady-state and time-resolved emission spectroscopy in solvent mixtures of toluene-ethanol and toluene-a cetonitrile at different temperatures. Emission spectra shift to the red up on addition of a polar solvent (PS) to toluene. Solvent mixtures show a muc h greater thermochromic shift to the blue in emission than the neat solvent s. This is explained by the decrease in temperature of the exothermic assoc iation of the polar solvent to the excited state. Emission spectra are time dependent in solvent mixtures in the ns timescale. The time evolution of t his emission is interpreted on the basis of the different solvation of the ground state and the emitting excited state. Stern-Volmer plots are obtaine d for the dependence of the spectral-shift characteristic time with [PS].