SOLUTE-SOLVENT INTERACTIONS IN THE GROUND-STATE AND IN ELECTRONIC EXCITED-STATES - DIPOLAR APROTIC TO POLAR PROTIC SOLVENT BLUE SHIFT OF NITROAROMATICS

The long-wavelength transition of some nitroaromatics was found to be uniformly blue shifted on transfer from dimethylformamide to methanol solvent. The enthalpies of transfer of the Franck-Condon excited states of these compounds were then determined by combining calorimetric and spectroscopic data. It was found that the enthalpies of transfer of the Franck-Condon excited states were uniformly endothermic into the hydrogen-bonding solvent and larger than the groundstate transfer enthalpies. As this is contrary to expectation for a transition that transfers negative charge to the nitro group, an estimate of the relaxed excited state transfer enthalpies was made using fluorescence measurements. It was found that the relaxed excited state has even more endothermic transfer enthalpies from the dipolar aprotic solvent to the polar protic solvent. © 1979, American Chemical Society. All rights reserved.