Self-trapping of the N–H vibrational mode in -helical polypeptides

Recent calculations on the formation of self-trapped amide group vibrational states in -helical polypeptides J. Chem. Phys. 124, 134907 2006 are extended to the amide N–H normal mode vibrations. First, the adiabatic N–H vibrational singleand two-exciton states are examined by treating the longitudinal chain coordinates as parameters. Then, in using the multiconfiguration time-dependent Hartree method coupled exciton-chain vibrational quantum dynamics are accounted for. Based on the respective exciton-chain vibrational wave function propagation the infrared transient absorption related to a sequential pump-probe experiment is calculated. The modulation of local amide vibrational energies by the longitudinal chain coordinates is found to have a pronounced effect on the broadening of absorption lines. Moreover, the ultrafast exciton transfer in the system is studied in order to characterize the dynamics of the self-trapped single-exciton states on a time scale below 10 ps. © 2006 American Institute of Physics. DOI: 10.1063/1.2402171