A study of the solution photophysics of the isomeric aminobenzoic acids, N, N-dimethylaminobenzoic acids and their methyl esters
type: CreativeWork
description: The solution photophysics of the isomeric aminobenzoic acids and N,Ndimethylaminobenzoic acids and their methyl esters were studied under a variety of conditions of solvent, pH, concentration and temperature. The most straightforward behaviour was obtained when the amino or N,N-dimethylamino substituent was in the meta- position relative to the carboxylic add or ester function. The amino compounds absorb with a peak between 300 and 325 nm depending on solvent, their fluorescence peaks lie between 350 and 410 rim. The corresponding N,N-dimethylamino compounds usually absorb and fluoresce some 20 - 30 rim to the red of these wavelengths. Both protonation and deprotonation of the ground state molecules takes place under weakly acidic conditions with pKi, values of approximately 3.0 and pK a values of approximately 5.0 being obtained. The observed variation in the fluorescence of the meta isomers with pH is largely caused by ground state equilibria. Förster cycle calculations suggest that the excited state pK a is little changed from the ground state whereas pKC is much smaller. This is in good agreement with the observed fluorescence data and the nature of the excited nglet state (usually some 10 -20 ns) than is seen for the other isomers. The fluorescence intensity of the meta- isomers was observed to rise with decreasing temperature, although this could possibly be attributed to absorbance changes. The photophysics of the corresponding ortho compounds is complicated by steric and hydrogen-bonding interactions especially in the compounds containing an N,N-dimethylamino group. The increased interaction between the two substituent groups leads to an increase in extinction coefficient and fluorescence quantum yield and a decrease in fluorescence lifetime for 2-aminobenzoic acid and its methyl ester compared to the meta derivatives. Spectral band positions, pK values and the effect of temperature on the fluorescence are similar in the two sets of compounds. The 2-N,Ndimet…
abstract: The solution photophysics of the isomeric aminobenzoic acids and N,Ndimethylaminobenzoic acids and their methyl esters were studied under a variety of conditions of solvent, pH, concentration and temperature. The most straightforward behaviour was obtained when the amino or N,N-dimethylamino substituent was in the meta- position relative to the carboxylic add or ester function. The amino compounds absorb with a peak between 300 and 325 nm depending on solvent, their fluorescence peaks lie between 350 and 410 rim. The corresponding N,N-dimethylamino compounds usually absorb and fluoresce some 20 - 30 rim to the red of these wavelengths. Both protonation and deprotonation of the ground state molecules takes place under weakly acidic conditions with pKi, values of approximately 3.0 and pK a values of approximately 5.0 being obtained. The observed variation in the fluorescence of the meta isomers with pH is largely caused by ground state equilibria. Förster cycle calculations suggest that the excited state pK a is little changed from the ground state whereas pKC is much smaller. This is in good agreement with the observed fluorescence data and the nature of the excited nglet state (usually some 10 -20 ns) than is seen for the other isomers. The fluorescence intensity of the meta- isomers was observed to rise with decreasing temperature, although this could possibly be attributed to absorbance changes. The photophysics of the corresponding ortho compounds is complicated by steric and hydrogen-bonding interactions especially in the compounds containing an N,N-dimethylamino group. The increased interaction between the two substituent groups leads to an increase in extinction coefficient and fluorescence quantum yield and a decrease in fluorescence lifetime for 2-aminobenzoic acid and its methyl ester compared to the meta derivatives. Spectral band positions, pK values and the effect of temperature on the fluorescence are similar in the two sets of compounds. The 2-N,Ndimet…
author: Revill, John Austin Timothy
language: en
keywords: F100 - Chemistry
date published: 1993-02
date modified: 2026-07-24T01:36:06Z
provider: University of Central Lancashire
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Central Lancashire