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Searching for solvent cavities via electron photodetachment: The ultrafast charge-transfer-to-solvent dynamics of sodide in a series of ether solvents
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10.1063/1.3245864
/content/aip/journal/jcp/131/15/10.1063/1.3245864
http://aip.metastore.ingenta.com/content/aip/journal/jcp/131/15/10.1063/1.3245864

Figures

Image of FIG. 1.
FIG. 1.

Molecular structure of the solvents studied in this work: THF, DEE, DME, and DG.

Image of FIG. 2.
FIG. 2.

Absorption spectra of sodide and the sodide CTTS photoproducts in the ethers shown in Fig. 1. Upper panel: absorption spectra of sodide in THF (black curve), DEE (blue dotted curve), DME (green dot-dashed curve), and DG (red dashed curve) as measured in our laboratory; since we could not independently determine the concentration of our samples, we assumed each spectrum had the same maximum extinction coefficient as sodide in THF. The gray dashed curve shows the spectrum of sodide in THF taken from the Gaussian–Lorentzian parameters presented in the literature (Ref. 47), which should be free of spectral contributions from potasside and/or scattering. Lower panel: absorption spectra of the solvated electron in THF (black curve), DEE (blue dotted curve), DME (green dot-dashed curve), and DG (red dashed curve) taken from Gaussian–Lorentzian parameters given in the literature (Ref. 68). The thin purple dashed curve shows the absorption spectrum of the sodium cation:electron TCP, , in THF, also taken from the literature (Ref. 47).

Image of FIG. 3.
FIG. 3.

Electron photodetachment dynamics following excitation at both the low-energy and high-energy sides of the CTTS band of sodide in both DME and DG. Upper panels: ultrafast absorption transients for sodide samples in DME (left panel) and DG (right panel) excited at 395 nm and probed at various wavelengths where the solvated electron absorbs in the near-IR. Lower panel: ultrafast absorption transients for sodide samples in DME (left panel) and DG (right panel) excited at 785 nm and probed at various wavelengths in the near-IR where the solvated electron absorbs. For ease of comparison, all the data have been normalized at the maximum transient absorbance. We note that the delayed appearance of the electron’s absorption and the complete lack of solvation dynamics also was seen for following excitation of sodide in both DEE and THF at these wavelengths (Refs. 14 and 18), suggesting that all four ether solvents contain cavities. The slight difference in the 1735 nm probe dynamics for the 395 nm excitation of sodide in DG (purple curve, upper right panel) is likely an artifact coming from the front cell wall of the sample.

Image of FIG. 4.
FIG. 4.

Solvent dependence of the electron photodetachment dynamics following CTTS excitation of sodide. Left panel: ultrafast absorption transients probing the solvated electron’s absorption near following CTTS excitation of sodide at 395 nm in THF (black curve), DEE (blue dotted curve), DME (green dot-dashed curve), and DG (red dashed curve). Right panel: ultrafast absorption transients probing the solvated electron’s absorption near following CTTS excitation of sodide at 785 nm in the same four solvents as in the left panel (same color scheme). Although the exact probe wavelength is slightly different in each of these scans, we know that the spectral dynamics of the detached electron are independent of probe wavelength, as seen in both Fig. 3 and Refs. 14, 15, and 18. The data have been normalized at the maximum transient absorption for ease of comparison.

Image of FIG. 5.
FIG. 5.

Electron photodetachment dynamics probed at 2130 nm following CTTS photoexcitation of sodide in THF (black curves), DME (green dot-dashed curves), and DG (red dashed curves) at 490 nm (upper panel), 575 nm (center panel) and 635 nm (lower panel). We were unable to cleanly extract electron photodetachment dynamics for sodide excited at intermediate wavelengths in DEE due to potasside contamination (Ref. 77). The data in each panel have been normalized to the maximum transient absorbance for ease of comparison.

Image of FIG. 6.
FIG. 6.

Fraction of long-lived electrons produced following CTTS photodetachment from sodide for different excitation wavelengths. The fraction is determined by the number of electrons that remain after photodetachment relative to the maximum number of electrons produced after photoexcitation from the data in Figs. 4 and 5. Data shown are for CTTS excitation of sodide in THF (black diamonds), DEE (blue inverted triangles), DME (green squares), and DG (red triangles).

Image of FIG. 7.
FIG. 7.

Energy level schematic illustrating our understanding of the relative positions of the localized sodide CTTS states and the disjoint states supported by the naturally occurring solvent cavities in THF (left), DME (center), and DG (right). The average energies of the sodide CTTS ground and optically allowed excited states are shown as the purple lines; the adjacent purple Gaussian distributions indicate the fact that these states are likely homogeneously broadened. The density of solvent-supported disjoint states in each liquid is portrayed as being proportional to the degree of color in the band: darker color indicates a higher density of disjoint states at a given energy (Refs. 14 and 17). The recombination dynamics for electrons photodetached from sodide suggest that the lowest solvent-supported states turn on at about the same energy in each solvent, but that the density of the solvent-supported states increases more rapidly in THF than in DME and much more rapidly than in DG.

Image of FIG. 8.
FIG. 8.

Long-time electron photodetachment dynamics probed at 2085 nm following CTTS excitation of sodide at 395 nm in THF (black curve), DEE (blue dotted curve), DME (green dot-dashed curve), and DG (red dashed curve). The data have been scaled to match the transient absorbance between and the -axis has been expanded for ease of comparison.

Image of FIG. 9.
FIG. 9.

Ultrafast dynamics of the initially created neutral sodium species and sodide bleach probed at 580 nm produced following 395 nm CTTS excitation of sodide in THF (black curve), DEE (blue dotted curve), DME (green dot-dashed curve), and DG (red dashed curve). The data has been normalized at the maximum transient absorbance for ease of comparison.

Image of FIG. 10.
FIG. 10.

Longer-time solvation dynamics of the TCP probed at 1110 nm following 395 nm CTTS excitation of sodide in THF (black curves), DEE (blue dotted curves) DME (green dot-dashed curves), and DG (red dashed curves). The initial rise and decay of the transients reflects absorption from the CTTS excited state and the small amount of fast recombination dynamics that still takes place at this excitation wavelength; the solvation dynamics of the TCP are reflected in the slower, 5–10 ps rise of the transient absorption (see text for details) (Ref. 84). The upper panel highlights the first of the dynamics and the lower panel shows the dynamics out to . The TCP solvation dynamics are essentially the same within error in THF, DME, and DG, but different (and much faster) in DEE. The data in both panels has been normalized at for ease of comparison.

Tables

Generic image for table
Table I.

Bulk properties of the ether solvents used in this study: is the index of refraction, is the viscosity, is the static dielectric constant, and is a measure of the solvatochromatic shift in the absorption spectrum of penta-tert-butyl pyridinium N-phenolate betaine in solution (see text). To the best of our knowledge the dielectric constant for DG has not been measured.

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/content/aip/journal/jcp/131/15/10.1063/1.3245864
2009-10-20
2014-04-25
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Searching for solvent cavities via electron photodetachment: The ultrafast charge-transfer-to-solvent dynamics of sodide in a series of ether solvents
http://aip.metastore.ingenta.com/content/aip/journal/jcp/131/15/10.1063/1.3245864
10.1063/1.3245864
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