Linear solvation energy correlation of the solvatochromic response of amino acid functionalized chromophores.

Solvatochromism of the long wavelength band in the electronic absorption spectra of N-(4-nitrophenyl)-L-proline, NLP, N-(4-nitrophenyl)-D-proline, NDP, and N-(4-nitro-phenyl)-trans-4-hydroxy-L-proline, NHP, was studied and quantitatively described with Kamlet-Taft solvent polarity parameters. To evaluate the environmental effects for NLP, NDP, and NHP, the UV-vis spectroscopic behavior of these compounds was also investigated as pure crystals, as a guest in 2,6-O-dimethyl-beta-cyclodextrin, and also when adsorbed on Aerosil 300 silica particles from nonhydrogen-bond accepting solvents. Excellent Kamlet-Taft solvatochromic correlations were established for the three compounds in most solvents. Multiparameter correlations show the existence of specific solute-solvent interactions. A strong positive solvatochromic behavior was found for these compounds, indicating that their dipole moments were higher in the excited singlet state than in the ground state.