Papers by Xanthipe Jordanides
Chemical Physics Letters, 2002
Two-photon absorption (TPA) resonance effects on the ultrafast pump-probe and transient grating (... more Two-photon absorption (TPA) resonance effects on the ultrafast pump-probe and transient grating (TG) responses of some transparent liquids excited with 400 nm pulses are demonstrated. The contribution of TPA and ground state Raman responses are separated in a TG experiment when the third-order polarization signal is viewed in the appropriate phase-matched direction as shown for the homodyne, TG response of CS 2. The pump-probe dichroic responses of liquids with (CS 2 and CH 3 I) and without (H 2 O, CCl 4 , and CH 3 OH) TPA resonances at 200 nm are compared. These results are discussed in the context of a perturbative third-order polarization treatment of TPA.
Chemical Physics, Aug 1, 1998
Two-dimensional Raman spectroscopy is used to probe the intermolecular interaction dynamics of CS... more Two-dimensional Raman spectroscopy is used to probe the intermolecular interaction dynamics of CS at 295 and 165 K. 2 The influence of nonlinear polarizability and liquid anharmonicity on the observable is discussed. It is found that the response at both temperatures is dominated by the nonlinear polarizability, which is most likely due to interaction-induced effects. A model using three Brownian oscillators to represent the collective motions on three time scales is unable to reproduce the 295 K data. At low temperature, the model presumably works better as a result of the timescale separation between the inertial and diffusive dynamics.
Springer series in chemical physics, 1998
Two-dimensional Raman spectroscopy using femtosecond pulse sequences is used to better understand... more Two-dimensional Raman spectroscopy using femtosecond pulse sequences is used to better understand the interactions between molecules and collective dynamics in liquids.
APS March Meeting Abstracts, Mar 1, 1998
An experimental study of the solvation dynamics in water is presented. Three pulse photon echo pe... more An experimental study of the solvation dynamics in water is presented. Three pulse photon echo peak shift measurements have been used to investigate the solute/solvent interactions of a fluorescein derivative in water. The data reveals that 70% of the decay occurs under 20fs, while the remaining amplitude corresponds to longer time solvation components. Implications of the ultrafast dynamics resulting from
Springer series in chemical physics, 2001
The dynamics of energy transfer processes in photosynthetic reaction centers and the light harves... more The dynamics of energy transfer processes in photosynthetic reaction centers and the light harvesting antenna LH2 are elucidated quantitatively using a new prescription for applying Forster theory to complex molecular aggregates. We conclude that the design of highly efficient light harvesting antenna systems generally cannot be predicted by pairwise Forster theory.
Journal of Physical Chemistry B, Feb 2, 2001
The remarkable efficiencies of solar energy conversion attained by photosynthetic organisms deriv... more The remarkable efficiencies of solar energy conversion attained by photosynthetic organisms derive partly from the designs of the light-harvesting apparatuses. The strategy employed by nature is to capture sunlight over a wide spectral and spatial cross section in chromophore arrays, then funnel the energy to a trap (reaction center). Nature's blueprint has inspired the conception of a diversity of artificial light-harvesting antenna systems for applications in solar energy conversion or photonics. Despite numerous, wide-ranging studies, truly quantitative predictions for such multichromophoric assemblies are scarce because Förster theory in its standard form often seems to fail. We report here a new framework within which energy transfer in molecular assemblies can be modeled quantitatively using a generalization of Förster's theory. Our results show that the principles involved in optimization of energy transfer in confined molecular assemblies are not revealed in a simple way by the absorption and emission spectra because such spectra are insensitive to length scales on the order of molecular dimensions.
Journal of Chemical Physics, Mar 22, 1999
Three-pulse photon echo peak shift measurements were employed to study aqueous solvation dynamics... more Three-pulse photon echo peak shift measurements were employed to study aqueous solvation dynamics. A new perspective of dielectric continuum theory ͓X. Song and D. Chandler, J. Chem. Phys. 108, 2594 ͑1998͔͒ aided in characterizing the system-bath interactions of eosin in water. Application of this theory provides solvation energies, which were used within the spectral density representation ͑͒, to calculate the experimental peak shift. Simulations with only solvation contributions to ͑͒, where a substantial amplitude of the solvation occurs within ϳ30 fs, are remarkably consistent with our data. Furthermore, simulations using this theoretical solvation spectral density and an experimentally determined intramolecular spectral density yield an excellent total simulation of the peak shift data over the entire dynamic range. Our experimental results substantiate predictions that interaction-induced polarizability effects, contributing via a ϳ180 cm Ϫ1 band in the spectral density, influence the initial dynamics.
Journal of Physical Chemistry B, Jan 10, 2004
It has been known for 30 years that the oxidized special pair radical cation P + is as efficient ... more It has been known for 30 years that the oxidized special pair radical cation P + is as efficient as the neutral ground-state species P in quenching excitation from the neighboring accessory bacteriochlorophylls B L and B M , but the mechanism for this process has remained elusive. Indeed, simple treatments based on application of standard Förster theory to the most likely acceptor candidate fails by 5 orders of magnitude in the prediction of the energy transfer rates to P +. We present a qualitative description of the electronic energy transfer (EET) dynamics that involves mixing of the strongly allowed transitions in P + with a manifold of exotic lowerenergy transitions to facilitate EET on the observed time scale of 150 fs. This description is obtained using a three-step procedure. First, multireference configuration-interaction (MRCI) calculations are performed using the semiempirical INDO/S Hamiltonian to depict the excited states of P +. However, these calculations are qualitatively indicative but of insufficient quantitative accuracy to allow for a fully a priori simulation of the EET and so, second, the INDO results are used to establish a variety of scenarios, empirical parameters that are then fitted to describe a range of observed absorption and circular dichroism data. Third, EET according to these scenarios is predicted using a generalized Förster theory that uses donor and acceptor transition densities, which together account for the large size of the chromophores in relation to the interchromophore spacings. The spectroscopic transitions of P + that facilitate the fast EET are thus unambiguously identified.
Journal of Physical Chemistry B, Feb 2, 2001
1640), a generalization of Förster theory is developed to calculate electronic energy transfer (E... more 1640), a generalization of Förster theory is developed to calculate electronic energy transfer (EET) in molecular aggregates. Here we apply the theory to wild-type and mutant photosynthetic reaction centers (RCs) from Rb. sphaeroides, as well as to the wild-type RC from Rps. Viridis. Experimental information from the X-ray crystallographic structure, resonance Raman excitation profiles, and hole-burning measurements are integrated with calculated electronic couplings to model the EET dynamics within the RC complex. Optical absorption and circular dichroism spectra are calculated at various temperatures between 10 K and room temperature, and compare well with the experimentally observed spectra. The calculated rise time of the population of the lower exciton state of P, P-, as a result of energy transfer from the accessory bacteriochlorophyll, B, to the special pair, P, in Rb. sphaeroides (Rps. Viridis) wild-type at 298 K is 193 fs (239 fs), and is in satisfactory agreement with experimental results. Our calculations, which employ a weak-coupling mechanism suggest that the upper exciton state of P, P + plays a central role in trapping excitation from B. Our ability to predict the experimental rates is partly attributed to a proper calculation of the spectral overlap J δR () using the vibronic progressions. The main advance we have made, however, is to calculate the electronic couplings V δR in terms of the molecular composition of donor and/or acceptor aggregates, rather than treating the acceptors P + and Pas point dipoles associated with each spectroscopic band. Thus, we believe our electronic couplings capture the essence of the many-body interactions within the RC. Calculations for EET in two mutants, (M)-L214H (the beta mutant) and (M)H202L (the heterodimer), are in reasonable agreement with experimental results. In the case of the heterodimer the agreement depends on a decrease in the electronic couplings between D M and the rest of the pigments.
Chemical Physics Letters, 2002
Abstract Two-photon absorption (TPA) resonance effects on the ultrafast pump–probe and transient ... more Abstract Two-photon absorption (TPA) resonance effects on the ultrafast pump–probe and transient grating (TG) responses of some transparent liquids excited with 400 nm pulses are demonstrated. The contribution of TPA and ground state Raman responses are separated in a TG experiment when the third-order polarization signal is viewed in the appropriate phase-matched direction as shown for the homodyne, TG response of CS 2 . The pump–probe dichroic responses of liquids with (CS 2 and CH 3 I) and without (H 2 O, CCl 4 , and CH 3 OH) TPA resonances at 200 nm are compared. These results are discussed in the context of a perturbative third-order polarization treatment of TPA.
The Journal of Physical Chemistry B, 2004
It has been known for 30 years that the oxidized special pair radical cation P + is as efficient ... more It has been known for 30 years that the oxidized special pair radical cation P + is as efficient as the neutral ground-state species P in quenching excitation from the neighboring accessory bacteriochlorophylls B L and B M , but the mechanism for this process has remained elusive. Indeed, simple treatments based on application of standard Förster theory to the most likely acceptor candidate fails by 5 orders of magnitude in the prediction of the energy transfer rates to P +. We present a qualitative description of the electronic energy transfer (EET) dynamics that involves mixing of the strongly allowed transitions in P + with a manifold of exotic lowerenergy transitions to facilitate EET on the observed time scale of 150 fs. This description is obtained using a three-step procedure. First, multireference configuration-interaction (MRCI) calculations are performed using the semiempirical INDO/S Hamiltonian to depict the excited states of P +. However, these calculations are qualitatively indicative but of insufficient quantitative accuracy to allow for a fully a priori simulation of the EET and so, second, the INDO results are used to establish a variety of scenarios, empirical parameters that are then fitted to describe a range of observed absorption and circular dichroism data. Third, EET according to these scenarios is predicted using a generalized Förster theory that uses donor and acceptor transition densities, which together account for the large size of the chromophores in relation to the interchromophore spacings. The spectroscopic transitions of P + that facilitate the fast EET are thus unambiguously identified.
In the accompanying paper (Scholes, G. D.; Jordanides, X. J.; Fleming, G. R. J. Phys. Chem. 2001,... more In the accompanying paper (Scholes, G. D.; Jordanides, X. J.; Fleming, G. R. J. Phys. Chem. 2001, 105, 1640, a generalization of Förster theory is developed to calculate electronic energy transfer (EET) in molecular aggregates. Here we apply the theory to wild-type and mutant photosynthetic reaction centers (RCs) from Rb. sphaeroides, as well as to the wild-type RC from Rps. Viridis. Experimental information from the X-ray crystallographic structure, resonance Raman excitation profiles, and hole-burning measurements are integrated with calculated electronic couplings to model the EET dynamics within the RC complex. Optical absorption and circular dichroism spectra are calculated at various temperatures between 10 K and room temperature, and compare well with the experimentally observed spectra. The calculated rise time of the population of the lower exciton state of P, P -, as a result of energy transfer from the accessory bacteriochlorophyll, B, to the special pair, P, in Rb. sphae...
Springer Series in Chemical Physics, 1998
An experimental study of the solvation dynamics in water is presented. Three pulse photon echo pe... more An experimental study of the solvation dynamics in water is presented. Three pulse photon echo peak shift measurements have been used to investigate the solute/solvent interactions of a fluorescein derivative in water. The data reveals that 70% of the decay occurs under 20fs, while the remaining amplitude corresponds to longer time solvation components. Implications of the ultrafast dynamics resulting from
Two-dimensional Raman spectroscopy is used to probe the intermolecular interaction dynamics of CS... more Two-dimensional Raman spectroscopy is used to probe the intermolecular interaction dynamics of CS at 295 and 165 K. 2 The influence of nonlinear polarizability and liquid anharmonicity on the observable is discussed. It is found that the response at both temperatures is dominated by the nonlinear polarizability, which is most likely due to interaction-induced effects. A model using three Brownian
Springer Series in Chemical Physics, 2001
The Journal of Physical Chemistry B, 2001
In the accompanying paper (Scholes, G. D.; Jordanides, X. J.; Fleming, G. R. J. Phys. Chem. 2001,... more In the accompanying paper (Scholes, G. D.; Jordanides, X. J.; Fleming, G. R. J. Phys. Chem. 2001, 105, 1640, a generalization of Förster theory is developed to calculate electronic energy transfer (EET) in molecular aggregates. Here we apply the theory to wild-type and mutant photosynthetic reaction centers (RCs) from Rb. sphaeroides, as well as to the wild-type RC from Rps. Viridis. Experimental information from the X-ray crystallographic structure, resonance Raman excitation profiles, and hole-burning measurements are integrated with calculated electronic couplings to model the EET dynamics within the RC complex. Optical absorption and circular dichroism spectra are calculated at various temperatures between 10 K and room temperature, and compare well with the experimentally observed spectra. The calculated rise time of the population of the lower exciton state of P, P -, as a result of energy transfer from the accessory bacteriochlorophyll, B, to the special pair, P, in Rb. sphaeroides (Rps. Viridis) wild-type at 298 K is 193 fs (239 fs), and is in satisfactory agreement with experimental results. Our calculations, which employ a weak-coupling mechanism suggest that the upper exciton state of P, P + plays a central role in trapping excitation from B. Our ability to predict the experimental rates is partly attributed to a proper calculation of the spectral overlap J δR ( ) using the vibronic progressions. The main advance we have made, however, is to calculate the electronic couplings V δR in terms of the molecular composition of donor and/or acceptor aggregates, rather than treating the acceptors P + and Pas point dipoles associated with each spectroscopic band. Thus, we believe our electronic couplings capture the essence of the many-body interactions within the RC. Calculations for EET in two mutants, (M)-L214H (the beta mutant) and (M)H202L (the heterodimer), are in reasonable agreement with experimental results. In the case of the heterodimer the agreement depends on a decrease in the electronic couplings between D M and the rest of the pigments.
The Journal of Physical Chemistry B, 2001
The remarkable efficiencies of solar energy conversion attained by photosynthetic organisms deriv... more The remarkable efficiencies of solar energy conversion attained by photosynthetic organisms derive partly from the designs of the light-harvesting apparatuses. The strategy employed by nature is to capture sunlight over a wide spectral and spatial cross section in chromophore arrays, then funnel the energy to a trap (reaction center). Nature's blueprint has inspired the conception of a diversity of artificial light-harvesting antenna systems for applications in solar energy conversion or photonics. Despite numerous, wide-ranging studies, truly quantitative predictions for such multichromophoric assemblies are scarce because Förster theory in its standard form often seems to fail. We report here a new framework within which energy transfer in molecular assemblies can be modeled quantitatively using a generalization of Förster's theory. Our results show that the principles involved in optimization of energy transfer in confined molecular assemblies are not revealed in a simple way by the absorption and emission spectra because such spectra are insensitive to length scales on the order of molecular dimensions.
The Journal of Physical Chemistry B, 1999
Photon echo spectroscopy is used to study the mechanisms of solvation dynamics in protein environ... more Photon echo spectroscopy is used to study the mechanisms of solvation dynamics in protein environments at room temperature. Ultrafast and additional multi-exponential long time scales are observed in the three-pulse photon echo peak shift data of the fluorescein dye eosin bound to lysozyme in aqueous solution. The dynamics of the solvated lysozyme are characterized with dielectric continuum models that integrate dielectric data for water with that for lysozyme. By comparing our data with previous results for eosin in water [Lang, M. J.; Jordanides, X. J.; Song, X.; Fleming, G. R. J. Chem. Phys. 1999, 110, 5584], we find that the total coupling of the electronic transition frequency of eosin to the nuclear motions of the aqueous lysozyme solution is smaller than in the aqueous solution. On an ultrafast time scale, solvation appears to be dominated by the surrounding water and not by the ultrafast internal motions of lysozyme. However, over long time scales, lysozyme does contribute significantly, either directly through motions of polar side chains or indirectly through reorientation of the water "bound" to the surface of the protein.
The Journal of Chemical Physics, 1999
Three-pulse photon echo peak shift measurements were employed to study aqueous solvation dynamics... more Three-pulse photon echo peak shift measurements were employed to study aqueous solvation dynamics. A new perspective of dielectric continuum theory ͓X. Song and D. Chandler, J. Chem. Phys. 108, 2594 ͑1998͔͒ aided in characterizing the system-bath interactions of eosin in water. Application of this theory provides solvation energies, which were used within the spectral density representation ͑͒, to calculate the experimental peak shift. Simulations with only solvation contributions to ͑͒, where a substantial amplitude of the solvation occurs within ϳ30 fs, are remarkably consistent with our data. Furthermore, simulations using this theoretical solvation spectral density and an experimentally determined intramolecular spectral density yield an excellent total simulation of the peak shift data over the entire dynamic range. Our experimental results substantiate predictions that interaction-induced polarizability effects, contributing via a ϳ180 cm Ϫ1 band in the spectral density, influence the initial dynamics.
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Papers by Xanthipe Jordanides