Amino-acid-functionalized solvatochromic probes

N-(4-nitrophenyl)-L-proline (2) has been obtained by a nucleophilic aromatic substitution reaction of 4-fluoronitrobenzene with L-proline. The corresponding amide derivatives 3-5 have been synthesized by peptide coupling of 2 with different amino acid derivatives and chiral amines. Solvatochromism of the long-wavelength UV/Vis band in the electronic absorption spectra of the compounds 2-5 has been studied and analyzed using the empirical Kamlet-Taft solvent polarity parameters pi* (dipolarity/polarizability), alpha (hydrogen bond donating ability), and beta (hydrogen bond accepting ability). Reasonable Kamlet-Taft solvatochromic correlations (r > 0.95) were established for the three amide derivatives 3-5 in a range of common solvents and three room temperature ionic liquids (RTILs). The UV/Vis absorption of the 4-nitroaniline derivative 2 showed a hypsochromic shift with increasing concentration due to intermolecular hydrogen bonded aggregate formation in protic solvents, which is not observed for compounds 3-5. Copyright (c) 2008 John Wiley & Sons, Ltd.