Spectrum, Kinetics, and Radiation Chemical Yield of Solvated Electrons in Hexamethylphosphoric Triamide

Shaede, Eric A.; Dorfman, Leon M.; Flynn, Garry J.; Walker, David C.

doi:10.1139/v73-582

Cited by 47 publications

(39 citation statements)

References 6 publications

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“…A similar situation occurs for electrons in amides, where polar C=O groups also point away from the cavity. 19,29 Thus, one can readily envision macro(bi)cycles with The experimental implementation of this scheme gave an unexpected result (section 3): placing just two cyano groups on the aliphatic scaffolding results in the formation of a molecular anion instead of the anticipated "solvated electron" like species.…”

Section: Electron Encapsulationmentioning

confidence: 99%

Toward Electron Encapsulation: Polynitrile Approach

Shkrob

Sauer

2006

J. Phys. Chem. A

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This study seeks an answer to the following question: Is it possible to design a supramolecular cage that would "solvate" the excess electron in the same fashion in which several solvent molecules do that co-operatively in polar liquids? Such an "encapsulated electron" would be instrumental for structural and dynamics studies of electron solvation and might be useful for molecular electronics. Two general strategies are outlined for "electron encapsulation," viz. electron localization using polar groups arranged on the (i) inside of the cage or (ii) outside of the cage. The second approach is more convenient from the synthetic standpoint, but it is limited to polynitriles. We demonstrate, experimentally and theoretically, that this second approach faces a formidable problem: the electron attaches to the nitrile groups forming molecular anions with bent C-C-N fragments. Since the energy cost of this bending is very high, for dinitrile anions in n-hexane, thebinding energies for the electron are very low and for mononitriles, these binding energies are lower still, and the entropy of electron 2. attachment is anomalously small. Density functional theory modeling of electron trapping by mononitriles in n-hexane suggests that the mononitrile molecules substitute for the solvent molecules at the electron cavity, "solvating" the electron by their methyl groups.We argue that such "solvated electrons" resemble multimer radical anions in which the electron density is shared (mainly) between C 2p orbitals in the solute/solvent molecules, instead of existing as cavity electrons. The way in which the excess electron density is shared by such molecules is similar to the way in which this sharing occurs in large diand poly-nitrile anions, such as 1,2,4,5,7,8,10,11-octacyano-cyclododecane -. The work thus reveals limitations of the concept of "solvated electron" for organic liquids: it might be impossible to draw a clear line between such species and a certain class of radical anions. It also demostrates the feasibility of "electron encapsulation."

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Section: Electron Encapsulationmentioning

confidence: 99%

Toward Electron Encapsulation: Polynitrile Approach

Shkrob

Sauer

2006

J. Phys. Chem. A

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“…The bulky nature of this solvent creates large cavities even before electron detachment [3]. Thus, the forward detachment can proceed rapidly since little solvent translational motion is needed, and the unusually high stability of the newly-formed solvated electron cavity could then result in the observed slow back ET time Overall, the results show that it is not sufficient to consider only the dielectric properties of a solvent when considering ET dynamics.…”

mentioning

confidence: 93%

“…The ~2 µm absorption of the solvated electron in HMPA is also similar to that in ethers. This is a result of the diffuse nature of the positive dipole of HMPA and the difficulty for large HMPA molecules to form cavities around negative particles with radii smaller than 4-5 Å [3], leading to a similar cavity size as for electrons in ethers. These factors also explain why the spectrum of Na¯ in HMPA is so similar to that in the ethers.…”

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confidence: 99%

Solvent Control of Electron Transfer Dynamics

Barthel¹,

Martini²,

Keszei³

et al. 2003

Springer Series in Chemical Physics

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Abstract. We investigate the charge-transfer-to-solvent (CTTS) dynamics of sodide i n several solvents. Since this CTTS system has only electronic degrees of freedom, the dynamics provide a window into how solvent motions control electron transfer.It is of great interest to understand how motions of solvent molecules control the dynamics of electron transfer (ET). Here we tackle this problem using the charge-transfer-to-solvent (CTTS) transition of sodide (Na¯) [1]. Absorption of a visible photon by Na¯ produces a localized excited state bound only by the polarization of the solvent, from which solvent motions promote electron detachment. Since the CTTS band of Na¯ is similar in a variety of ethers and amines [2], we can use ultrafast spectroscopy to determine how the local solvent structure controls the dynamics of CTTS detachment. We find that there is a subps delayed detachment of the electron from the CTTS excited state (Na¯*) followed by back ET (geminate recombination) on a time scale of a few ps. For ether solvents, the back ET times correlate with solvent polarity, with more polar ethers having shorter back ET times. We also find that this trend does not hold in non-ether solvents, and there appears to be no correlation of the forward ET (detachment) time with solvent polarity. This points to the importance of local solvent structure in determining the CTTS detachment dynamics. Figure 1A shows the absorption spectrum of the Na¯ CTTS transition in tetrahydrofuran (THF), tetrahydropyran (THP), diethyl ether (DEE), and hexamethylphosphoramide (HMPA); Figure 1B shows the chemical structures of each of these solvents. The spectrum of Na¯ is similar not only in the three ethers but also the more polar HMPA. The ~2 µm absorption of the solvated electron in HMPA is also similar to that in ethers. This is a result of the diffuse nature of the positive dipole of HMPA and the difficulty for large HMPA molecules to form cavities around negative particles with radii smaller than 4-5 Å [3], leading

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“…In our investigations of the optical absorption spectrum of the solvated electron (1)(2)(3)(4)(5)(6) in polar liquids we have, over the past four years, focussed much of our attention on the important question of whether., and to what extent, short-range interactions may be a dominant factor, along with the bulk solvent properties, in determining.the optical properties of the solvated electron. We have approached this question with three different types of experiments: (a) a broad survey of the spectrum of esol in different classes of compounds (3)(4)(5)(6) with a view to determining whether the spectral grouping (3,7) of these absorptions showed any marked dependence upon class of compouhd;…”

Section: Introductionmentioning

confidence: 99%

“…We have approached this question with three different types of experiments: (a) a broad survey of the spectrum of esol in different classes of compounds (3)(4)(5)(6) with a view to determining whether the spectral grouping (3,7) of these absorptions showed any marked dependence upon class of compouhd;…”

Section: Introductionmentioning

confidence: 99%

Optical absorption spectrum of the solvated electron in polar liquids and in binary solutions

Dorfman

Gavlas

1974

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Spectrum, Kinetics, and Radiation Chemical Yield of Solvated Electrons in Hexamethylphosphoric Triamide

Cited by 47 publications

References 6 publications

Toward Electron Encapsulation: Polynitrile Approach

Toward Electron Encapsulation: Polynitrile Approach

Solvent Control of Electron Transfer Dynamics

Optical absorption spectrum of the solvated electron in polar liquids and in binary solutions

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