Photon Echo Peak Shift Measurements Research Articles

Ultrafast Solvation Dynamics in Room Temperature Ionic Liquids Observed by Three-Pulse Photon Echo Peak Shift Measurements

Three-pulse photon echo peak shift (3PEPS) measurement was applied to the investigation of the primary part (<100 ps) of the solvation dynamics in a series of imidazolium ionic liquids (IL) with an organic dye, oxazine 4 (Ox4), utilized as a probe. The ultrafast solvent response in the range of ≤300 fs exhibited dependence on the square root of the anion mass, indicating its relation with the inertial motion of anion. The inertial response of ILs with chloride anion was the fastest among other ILs with heavier and larger anions. Because Ox4 is a cationic dye, it holds a stronger interaction with the anion of IL, thus the ultrafast part of the solvation is strongly affected by the inertial motion of anions. The second solvation component in the range of ≤3.5 ps had better correlation with the reduced mass and the size of both ions included, indicating the beginning of a more global solvation process.

Three-Pulse Photon Echo Peak Shift Measurements of Capped CdSe Quantum Dots

In this article, the results of femtosecond three-pulse photon echo peak shift (3-PEPS) measurements are reported for a series of cadmium selenide core−shell semiconductor nanocrystals. The peak shift data were found to be highly dependent on the shell compositions and particle morphologies. The static inhomogeneity parameter was found to vary from 10 cm−1 for highly isotropic particles to 170 cm−1 for particles with a broad size distribution. We also discuss the high-frequency (≈212 cm−1) longitudinal optical (LO) phonon and the low-frequency (≈13−19 cm−1) longitudinal acoustic (LA) phonon modes (ω00) and how the damping times and frequencies also depend on the choice of capping material.

Dephasing in semiconducting single-walled carbon nanotubes induced by exciton-exciton annihilation

Three-pulse photon echo peak-shift measurements were performed on semiconducting single-walled carbon nanotubes embedded in a polymer matrix at room temperature. We found a striking dependence of the peak shift on the excitation intensity. Numerical simulations based on an interacting-boson model demonstrate that the intensity dependence originates from a highly nonlinear optical response initiated by exciton-exciton annihilation.

Femtosecond Photon Echo Spectroscopy of Semiconducting Single-Walled Carbon Nanotubes

Three-pulse photon echo peak shift measurements were performed on semiconducting single-walled carbon nanotubes embedded in polymer matrix at room temperature. Simultaneous modeling of the peak shift data in the limit of zero-intensity and the linear absorption spectrum enable us to extract an intrinsic homogeneous line width of 178 cm(-1), an inhomogeneous width of 698 cm(-1), and a Huang-Rhys factor of 0.04 for the radial breathing mode vibration. The peak shift data when combined with two-pulse photon echo and pump-probe measurements allows us to determine a pure exciton dephasing time scale of 78 fs at room temperature.

Strongly Interacting Organic Conjugated Dendrimers with Enhanced Two-Photon Absorption

We report a strongly interacting new dendrimer system with an extended spectroscopic unit (coherent domain) beyond the trimer configuration. This report focuses on the mechanism of enhancement of the two-photon absorption (TPA) response of this material as a function of the dendrimer generation number. This enhancement is strongly correlated to the size and geometry of the spectroscopic unit in a strongly interacting macromolecular system. These systems are investigated by a wide variety of time-resolved spectroscopy methods including time-resolved fluorescence, transient absorption, three-pulse photon echo peak shift measurements as well as TPA cross section measurements. The extensive combination of modern spectroscopic methods strongly indicates that the spectroscopic unit (domain) in high generations covers the G1 (nine linear building blocks) and exceeds the trimer size.

Ultrafast Exciton Dynamics in a Branched Molecule Investigated by Time-Resolved Fluorescence, Transient Absorption, and Three-Pulse Photon Echo Peak Shift Measurements

The excited-state dynamics of a branched octupolar molecule (tris-4,4‘,4‘ ‘-(4-nitrophenilethynyl)triphenylamine (T-NPTPA)) with charge-transfer character is investigated by complementary measurements of time-resolved fluorescence, transient absorption, and three-pulse photon echo peak shift. The data are compared with those obtained for the linear molecule dimethylnitroaminotolane (DMNAT) representing a linear building block of the octupolar system. Time-resolved fluorescence as well as transient absorption experiments showed the presence of an intermediate C3 symmetry state for the trimer with a depolarization time faster than ∼50 fs. Three-pulse photon echo peak shift measurements for the trimer revealed a large initial fast component of the peak shift decay. The initial peak shift during the first 100 fs was found to be much higher for the trimer as compared to the linear building block. This is in accordance with the time-resolved anisotropy results suggesting a different character of the initial excitation of the trimer. The higher peak shift value for the trimer suggests a smaller total coupling of electronic transition frequency to the nuclear motions, which may be the result of the delocalized character of this initial excited state. A residual peak shift (∼2 fs) at long population times was also observed and was interpreted as an indication of the residual static inhomogeneity (inhomogeneous broadening) in the system.

Vibrational Dynamics of the OH Stretching Mode of Water in Reverse Micelles Studied by Infrared Nonlinear Spectroscopy

ABSTRACTVibrational dynamics of the OH stretching mode of water in the water pool of reverse micelles (H2O/Aerosol OT (AOT)/isooctane) are studied by nonlinear infrared spectroscopy such as transient grating method and three-pulse photon echo peak shift measurements. The W0 value (W0 =[H2O]/[AOT]) is changed from 2 to 40, which corresponds to a water pool diameter of a few nm to about 20 nm. Polarization dependent transient grating experiments show rapid anisotropy decay of the OH stretching mode, which could be due to resonant intra and intermolecular energy transfer. From the three-pulse photon echo peak shift experiments, the spectral diffusion is found to be dependent on W0.

Ultrafast Energy Transfer in LHC-II Revealed by Three-Pulse Photon Echo Peak Shift Measurements

We report the results of three-pulse photon echo peak shift (3PEPS) measurements on the light-harvesting complex II (LHC-II) of the green algae Chlamydomonas reinhardtii. Experiments were performed at two different excitation wavelengths, 670 and 650 nm, corresponding to Chl-a and Chl-b excitation, respectively. The 3PEPS data are analyzed using a new theory that incorporates the effect of energy transfer on third-order response functions. Our theoretical model separates energy transfer dynamics from the solvation dynamics arising from coupling of the electronic transitions to the protein environment. We suggest that the protein fluctuations can be described by an ultrafast solvation on a sub-100 fs time scale and a long time correlation (static disorder). Decay of the 670 nm peak shift reveals spectral equilibration time scales for Chl-a molecules that range from 300 fs to 6 ps and agree well with other experiments. 3PEPS data at 650 nm (Chl-b excitation) reveal rapid Chl-b to Chl-b energy transfer (<1 p...

Aqueous solvation dynamics studied by photon echo spectroscopy

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 (1998)] 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 ρ(ω), to calculate the experimental peak shift. Simulations with only solvation contributions to ρ(ω), where a substantial amplitude of the solvation occurs within ∼30 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 ∼180 cm−1 band in the spectral density, influence the initial dynamics.

The interaction of solutes with their environments

The origins of electronic spectral broadening in solutions, glasses and proteins are discussed via three pulse stimulated echo peak–shift measurements. Spectral densities for dye molecules in polar solutions are presented and discussed in terms of molecular models for the dynamics. The breakdown of the harmonic bath picture at low frequencies is presented. Finally, echo measurements on light harvesting complexes of purple bacteria are presented and it is shown that the energy transfer timescale can be obtained from peak–shift measurements.

Three pulse echo peak shift measurements on the B820 subunit of LH1 of Rhodospirillum rubrum

Three pulse photon echo peak shift measurements (3PEPS) of the detergent isolated B820 subunit of the light harvesting complex of Rhodospirillum rubrum are presented and compared with 3PEPS data for the LH1 complex of Rhodobacter sphaeroides. The comparison suggests that the 90 fs component of LH1 3PEPS is indeed the energy transfer component. The striking similarity between 3PEPS of LH1 and B820 subunit also suggests that excitation is delocalized over only a dimer unit.

Third-order nonlinear time domain probes of solvation dynamics

Several closely related third-order nonlinear time-resolved spectroscopic techniques, pump/probe transient absorption, transient grating, and three pulse stimulated photon echo peak shift measurements, are investigated theoretically and experimentally. It is shown in detail, through the consideration of response functions and numerical simulations including both finite pulse durations and detuning from exact resonance, how the solvation dynamics are manifested in these third-order nonlinear time-resolved spectroscopies. It is shown that the three pulse stimulated photon echo peak shift measurement and the transient grating measurement can give accurate dynamical information, whereas transient absorption may not be a reliable technique for a study of solvation dynamics in some cases. The contribution of very slow or static (inhomogeneous) components to the dynamics, however, can only be obtained from the three pulse echo peak shift measurements. Comprehensive experimental measurements are presented to illustrate and corroborate the calculations. We show that it is possible to separate the intramolecular vibrational and solvent contributions to the dephasing (or optical lineshape). Furthermore it is shown that the solvation of polar solutes in polar protic solvents has rather universal characteristics. The initial ultrafast process, usually identified as an inertial response of solvent molecules, occurs on a ∼100 fs time scale, and is essentially identical in methanol, ethanol, and butanol. The amplitude of this ultrafast component does, however, decrease with increasing alcohol size in 1-alkanols. The diffusive (≳0.5 ps) regime of the solvation process shows a strong solvent dependence, and may be described satisfactorily by dielectric relaxation theories.