Intramolecular Proton Transfer Effects on 2,6-diaminopyridine

Abstract

The photophysical behaviour of 2,6-diaminopyridine (DAP) has been studied in solvents of different polarity, pH, beta-cyclodextrin (beta-CD) and compared with 2-amino pyridine (2AP). The inclusion complex of both molecules with beta-CD are analysed by UV-visible, fluorimetry, FT-IR, (1)H NMR, SEM and AM1 methods. The solvent studies shows i) DAP gives more red shifted absorption and emission maxima than 2AP molecule and ii) addition of amino group in 2AP effectively increase the resonance interaction in the pyridine ring. A regular red shift observed in acidic pH solutions suggests intramolecular proton transfer (IPT) present in both molecules. beta-CD studies indicates i) in pH approximately 7, a regular red shifted absorption and emission maxima observed in AP molecules suggests pyridine ring encapsulated in to the beta-CD cavity (1:1 inclusion complex formed) and ii) in pH approximately 1, a blue shifted absorption maxima noticed in 2AP, is due to protonated amino group deeply encapsulated in to the hydrophobic part of the beta-CD cavity.