Influence of Prototropic Reactions on the Absorption and Fluorescence Spectra of Methyl p-dimethylaminobenzoate and Its Two Ortho Derivatives

• Published in: Journal of fluorescence Vol. 21; no. 4; pp. 1749 - 1762
• Main Authors: Józefowicz, M., Aleksiejew, M., Abramov, A. V., Ling, S., Gutowski, M., Heldt, J., Heldt, J. R.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.07.2011
• Subjects: 4-Aminobenzoic Acid - chemical synthesis; 4-Aminobenzoic Acid - chemistry; Analytical Chemistry; Biochemistry; Biological and Medical Physics; Biomedical and Life Sciences; Biomedicine; Biophysics; Biotechnology; Molecular Structure; Original Paper; para-Aminobenzoates; Spectrometry, Fluorescence; Stereoisomerism; Methyl p-dimethylaminobenzoate; Absorption and emission spectra; Quantum-chemical calculations; Fluorescence quenching
• ISSN: 1053-0509; 1573-4994
• DOI: 10.1007/s10895-011-0870-y

The influence of prototropic reactions on the spectral characteristics of methyl p-dimethylaminobenzoate (I) and its o-methoxy (II) and o-hydroxy (III) derivatives has been studied using steady-state spectroscopic technique and quantum-chemical calculations. This study concerns the solvent-induced shift of the absorption, locally excited (LE) and intramolecular charge transfer (ICT) fluorescence bands in the neat tetrahydrofuran (THF) and its hydrochloric acid solutions at different HCl concentrations. On the basis of the experimental results and quantum-chemical calculations, it was shown that in a hydrochloric acid solution the studied molecules exist as a mixture of neutral, mono-, and dicationic forms. Additionally, the results of spectroscopic measurements were used to calculate, according to the Benesi-Hildebrand method, the equilibrium constants of protopropic reactions in the ground, S 0 , and excited, S 1 , states. Our findings predestine molecules I and II to be used as acid fluorescence probes in a region of 0–2.5 M of [H + ] concentrations.