Hydrogen bonding NH/pi interactions between betacarboline and methyl benzene derivatives

In the presence of benzene, toluene, m-xylene, mesitylene and durene, the p yrrolic NH stretching band of betacarboline, 9H-pyrido[3,4-b]indole, and it s 1-methyl derivative, harmane, in tetrachloroethane diminishes in intensit y while a new red-shifted band grows up. The shifts of the associated bands increase linearly with the pi -electron density of the substrates. These s pectral changes are attributed to the formation of 1:1 molecular associatio n complexes between the betacarbolines and the benzenoid substrates. The co mplexes are stabilized by the hydrogen-bonding interaction between the pyrr olic NH group of betacarboline and the pi -delocalized electrons of the ben zene derivatives. The influence of these NH/pi hydrogen-bonding interaction s in the fluorescence spectra of betacarboline is discussed. (C) 2001 Elsev ier Science B.V. All rights reserved.