Intramolecular charge transfer effects on 3,5-diaminobenzoic acid – Effect of β-cyclodextrin, pH and solvents

Department of Chemistry, Annamalai University, Annamalainagar-608 002, Tamilnadu, India

E-mail : drrajendiran@rediffmail.com Fax : 91-4144-238080

Manuscript received online 29 July 2013, revised 22 August 2013, accepted 29 August 2013

Absorption and fluorescence spectra of 3,5-diaminobenzoic acid (DABA) were analysed in different solvents, pH and β-cyclodextrin (β-CD) and compared with 3-aminobenzoic acid (ABA). A large red shifted absorption and emission maxima in non-polar solvents indicate ICT present in DABA molecule. Effects of β-CD on DABA molecule were studied in different buffer solutions (pH ~1, pH ~7 and pH ~10). In all the above pHs, DABA forms 1 : 1 inclusion complex. Dual luminescence is observed at pH~1 and pH~7 solutions which shows that intramolecular charge transfer present in both pHs. The broad spectral maximum at pH ~10 indicates that intramolecular proton transfer is present in DABA molecule. Proton transfer reactions in β-CD medium indicates COOH group present in the hydrophilic part, whereas amino group present in the hydrophobic part of the β-CD cavity. The present study demonstrates that in DABA, ICT interactions play a significant role in all solvents and β-CD.