Based on a correct quantum dynamical description, exciton formation and self-trapping in alpha-helical polypeptides is reinvestigated. The studies are focused on the amide 1 high-frequency vibration of the peptide group and account for their modulation by longitudinal helix vibrations. First, the adiabatic single- and two-exciton states are analyzed for a chain of 10 peptide units, whereby the presence of two types of self-trapped amide 1 two-exciton states is confirmed. In a second step, by using the multi-configuration time-dependent Hartree method an exact quantum description is achieved for the complete exciton helix-vibrational states. The computational approach incorporating up to nine helix coordinates is used to calculate the infrared linear absorbance. Moreover, excitation energy motion through the chain is characterized. sigma 2005 Elsevier B.V. All rights reserved.