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Spectroscopically relevant properties in photosynthetic reaction centers change during charge separation. In this paper, we focus on incorporation of the complete set of environmental fluctuations in the modeling of the nonlinear spectra of molecular aggregates. The model is applied in simulations of two-dimensional electronic spectra of a photosynthetic reaction center at low temperature (5 K), where spectral lines are narrow, such that more features can be resolved. We show that vertical cross sections of the simulated two-dimensional spectra (with all populations in the lowest excited state) reveal transient hole-burned spectra excited resonantly within the B band in agreement with experiment, thus providing new insight into environmental fluctuation parameters of Rhodobacter sphaeroides at low temperatures. Correlated fluctuations of molecular parameters are found to be necessary to describe charge separated configurations of molecular excited states. [ABSTRACT FROM AUTHOR]

Molecular conformational changesin electronic excited states play a key role in numerous light-activatedprocesses. In the case of porphyrin oligomers intramolecular twistinginfluences energy and charge transport dynamics. Here we address thetwisting reaction in both ground and excited states in a model porphyrindimer, employing two-dimensional electronic spectroscopy (2D ES).By spreading the information over excitation and detection frequencies,cross-peaks reveal the twisting reaction in both the ground and excitedstates unambiguously and distinctly from other dynamics. A quasi-barrierlessplanarization reaction is observed in the excited state on a tensof picoseconds time scale. This is accompanied by a spectral narrowing,indicative of a reduction in conformational disorder. The reversereaction is suppressed in the excited state due to a steep activationenergy barrier. However, in the ground state the barrier is withinthe thermal energy distribution, and therefore contributions fromreverse and forward reactions could be observed on the subnanosecondtime scale. Crucially 2D ES enables simultaneous assessment of groundand excited state reactions through analysis of different spectralregions on the 2D spectral maps. [ABSTRACT FROM AUTHOR]

The electronic absorption spectrumof 9,9-dimethyl-2,7-dinitrofluoreneradical anion in HMPA displays both a NIR intervalence charge transferand a visible excited state mixed valence transition. These transitionscontain a similar vibronic progression resulting from molecular orbitalsthat are common to both transitions. Vibrational frequency and intensitydata are acquired from the resonance Raman spectrum and used to calculatea best fit for the absorption spectrum. The normal coordinate distortionsare analyzed in terms of the electronic changes for both transitionsto explain their similarity. The Raman scattering intensity decreasesat lower excitation wavelength as a result of Raman de-enhancementcaused by interference between neighboring excited states. [ABSTRACT FROM AUTHOR]

The potential energy curves and spectroscopic constantsof theground and excited states of the RbAr van der Waals system have beendetermined using a one-electron pseudopotential approach. This techniqueis used to replace the effect of the Rb+core and the electron–Arinteractions by effective potentials. The core–core interactionfor Rb+Ar was incorporated using the accurate CCSD(T) potentialof Hickling et al. [Hickling,H. L.; Viehland, L. A.; Shepherd, D. T.; Soldán, P.; Lee, E.P. F.; Wright, T. G. Phys. Chem. Chem. Phys.2004, 6, 4233−4239]. This model reduces the number of activeelectrons of the RbAr van der Waals systems to just the single valenceelectron, permitting the use of very large basis sets for the Rb andAr atoms. Using this approach, the potential energy curves of theground and excited states dissociating into Rb(5s, 5p, 4d, 6s, 6p,6d, and 7s) + Ar are calculated at the SCF level. Spin–orbitinteraction was also considered within a semiempirical scheme forthe states dissociating into Rb(5p) and Rb(6p). Spectroscopic constantsare derived and compared with the available theoretical and experimentaldata. Such comparisons for RbAr show very good agreement for the groundand the first excited states. Furthermore, we have predicted the B2Σ+1/2← X2Σ+, A2Π1/2← X2Σ+, A2Π3/2←X2Σ+, A2Π3/2← X2Σ+, 52Σ+← X2Σ+, 32Π1/2← X2Σ+, and 32Π3/2← X2Σ+absorptionspectra. [ABSTRACT FROM AUTHOR]

The electronic origin bands A and B of 5-hydroxyindolewere measuredusing rotationally resolved electronic spectroscopy. From comparisonof the experimental rotational constants to the results of ab initiocalculated structures, we could make the assignment of band A beingdue to the synconformer and of band B being dueto the anticonformer. These conformers, which differin the orientation of the hydroxy group with respect to the rest ofthe molecule, have considerably different S1state lifetimes. The most probable explanation for this surprising finding isa different conical intersection of the ππ* states ofboth conformers with the repulsive πσ* state. [ABSTRACT FROM AUTHOR]