Proton-Transfer-Induced Fluorescence in Self-Assembled Short Peptides.

We employ molecular dynamics (MD) and time-dependent density functional theory (TDDFT) to explore the fluorescence of hydrogen-bonded dimer and trimer structures of cyclic FF (Phe-Phe) molecules. We show that in some of these configurations a photon can induce either an intra-molecular proton transfer, or an inter-molecular proton transfer that can occur in the excited S1 and S2 states. This proton transfer, taking place within the hydrogen bond, leads to a significant red-shift that can explain the experimentally observed visible fluorescence in biological and bioinspired peptide nanostructures with a β-sheet biomolecular arrangement.

Analysis of nonlinear gain-induced effects on short-pulse amplification in doped fibers by use of an extended power equation.

Optical pulse amplification in doped fibers is studied using an extended power transport equation for the coupled pulse spectral components. This equation includes the effects of gain saturation, gain dispersion, fiber dispersion, fiber nonlinearity, and amplified spontaneous emission. The new model is employed to study nonlinear gain-induced effects on the spectrotemporal characteristics of amplified subpicosecond pulses, in both the anomalous and the normal dispersion regimes.