Intramolecular charge transfer associated with hydrogen bonding effects on 2-aminobenzoic acid

Effect of solvents, buffer solutions of different pH and P-cyclodextrin (beta-CD) on the absorption and fluorescence spectra of 2-aminobenzoic acid (2ABA) have been investigated. The inclusion complex of 2ABA with P-CD is discussed by semiempirical quantum calculations (AMI), absorption, emission, FT-IR, H-1 NMR and scanning electron microscope (SEM). The Stokes shifts in 2ABA is correlated with different polarity scales suggest that 2ABA molecule is more polar in the S I state. The increase in the excited state dipole moment values and P-CD studies confirm that the presence of intramolecular charge transfer (ICT) in 2ABA. Acidity constants for different prototropic equilibria of 2ABA in the So and S I states are calculated. P-CD studies shows that (i) at pH similar to 1, 2ABA forms 1: 1 inclusion complex with P-CD, whereas at pH similar to 7, it forms mixture of 1: 1 and 1:2 inclusion complex and (ii) at pH similar to 1, appearance of dual luminescence in higher P-CD solutions indicates carboxyl and amino groups present in the hydrophobic part of the P-M. A mechanism is proposed to explain the inclusion process. (c) 2006 Elsevier B.V. All rights reserved.