Zeeman shift of two-dimensional optical signals of Mg-porphyrin dimers with circularly polarized beams.

Two-dimensional (2D) electronic spectra of Mg-porphyrin dimers with circularly polarized laser pulses are simulated for two molecular geometries. The Zeeman shift of the non-chiral 2D spectra induced by a magnetic field highlights spectral regions that are dominated by exciton states with large total angular momentum, and are particularly sensitive to the geometry. These 2D shifts show much higher sensitivity to the molecular array than the absorption spectrum shifts.

Probing ring currents in Mg-porphyrins by pump-probe spectroscopy.

Theoretical studies of Manz et al. have shown that upon excitation of a Mg-porphyrin molecule with a circularly polarized laser pulse, a ring current can be generated that is much stronger than what can be induced by means of an external magnetic field with present technology. We show that the circular dichroism signal of a Mg-porphyrin molecule that has been excited to a state with an inner ring current is proportional to the magnitude of the probability of this ring current and can be used for the detection of this current.

Dissecting two-dimensional ultraviolet spectra of amyloid fibrils into beta-strand and turn contributions.

We present an analysis of the contributions of various secondary structure elements of the amyloid β-protein to the two-dimensional far ultraviolet (2DFUV) signal of an amyloid fibril model. The contributions of the turns and the β-strands are affected by the geometry of the backbone peptide amide π → π* transition dipoles, the backbone interamide coupling in the excited state, and the exciton delocalization. These contributions are clearly distinguishable in the xyxy-xyyx pulse polarization configuration.

On the influence of nonlocal molecular vibrations and charge transfer on the spectra of aggregated push-pull chromophores.

Through their fluorescence spectrum, aggregates of push-pull chromophores are good reporters of their microenvironment temperature and polarity. The understanding of the fluorescence and charge-separation dynamics in arrays composed of this type of species is consequently of considerable interest. In this article, we study the effect of charge fluctuations induced by molecular nonlocal vibrations on the electronic coupling between a pair of linear push-pull chromophores, for side-to-side or head-to-tail orientations, using a valence-bond charge-transfer (VB-CT) model and the Redfield equation.

On the role of dissipation on the Casimir-Polder potential between molecules in dielectric media.

An expression for the Casimir-Polder potential between molecules in a homogeneous dispersive and absorptive dielectric medium is derived. The effect of retardation on the interaction energy is discussed by examining the wave-zone and nonretarded limits of the potential. Unlike Lifshitz theory, the interaction energy is not derived from the potential between macroscopic bodies.

Effect of medium chirality on the rate of resonance energy transfer.

Resonance energy transfer (RET) between two chromophores in an absorptive and dispersive chiral medium is investigated using a quantum electrodynamical formulation. To accurately describe such an environment involves the introduction of electric displacement and auxiliary magnetic field operators that are solutions of the Drude-Born-Fedorov equations and the time-harmonic Maxwell equations. Perturbation theory within the electric and magnetic dipole approximation is used in the derivation of the probability amplitude for energy transfer.