FTIR and fluorescence studies on the ground and excited state hydrogen-bonding interactions between 1-methylindole and water in water-triethylamine mixtures

The ground and excited state pi-hydrogen-bonding interactions between 1-methylindole, MI, and water have been investigated in water-triethylamine, water-TEA, mixtures. FTIR measurements performed on the OH stretching bands of the water-TEA clusters show that, upon MI addition, the typical bands of the water-TEA system at 3348 cm(-1), 3440 cm-1, 3545 cm-1 and 3682 cm-1 diminish, whereas two new absorption bands at 3316 cm(-1) and 3654 cm(-1) grow up. These spectral changes have been rationalised assuming the formation of only one 1:1 water-MI complex, in which the dangling protons in the water-TEA clusters are hydrogen bonded to the pi-cloud of the MI aromatic ring. Steady state and time resolved fluorescence measurements provide additional proofs on the ground state formation of a fluorescent OH center dot center dot center dot pi hydrogen bonded complex. The relevance that the present and the previously reported results could have on the indole ring photophysics is discussed. (c) 2007 Elsevier B.V. All rights reserved.