Direct observation of ion-pair dynamics

Masnovi, John; Kochi, Jay K.

doi:10.1021/ja00312a014

Cited by 80 publications

(51 citation statements)

References 3 publications

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“…(Although in some cases there are appreciable changes in the spectra of carbocations on increasing the concentrations of added perchlorate (14), in our reactions the position of the main absorption maximum in spectra of solutions of the carbocation is essentially the same on changing the concentration of electrolyte from 0.5 to 3.5 mol dm -3 .) Finally, we assume that step (v) of Scheme 1 constitutes a postequilibrium with equilibrium constant K 5 (equal to k 5 /k -5 ), i.e., [R + ||X -] = K 5 [R + ][X -] and that maintenance of this equilibrium does not affect the overall rate of equilibration (13). With no further assumptions, these approximations allow derivation of the following equation:…”

Section: Discussionmentioning

confidence: 99%

“…[11] gives eq. [13] where K 2 = k 2 /k -2 and values for K 1 K 2 k 3 and K 1 k 4 obtained by linear regression of k f against…”

Section: Discussionmentioning

confidence: 99%

“…From the results for the influence of perchloric acid on the reaction parameters at nonconstant ionic strength (Table 6), we obtain the following using eq. [13] (linear regression of k f against [ClO 4 -]) and eq. [15] (linear regression of 1/k r against [ClO 4 -]): K 1 K 2 k 3 = 8.3 ± 0.4 dm 3 mol -1 s -1 , K 1 k 4 = 7.9 ± 0.6 dm 6 mol -2 s -1 , k -3 = 122 ± 3 s -1 , K 5 = 1.80 ± 0.07 dm 3 mol -1 , K R + = 14.7 ± 0.8 mol dm -3 , and k 4 = 3200 dm 3 mol -1 s -1 .…”

Section: Influence Of Hydronium Ion Concentrationmentioning

confidence: 99%

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The 4,4'-dimethoxytrityl carbenium ion by ionization of 4,4'-dimethoxytrityl alcohol in acetonitrile - aqueous perchloric and nitric acids containing electrolytes: kinetics, equilibria, and ion-pair formation

Crugeiras¹,

Maskill²

1999

Can. J. Chem.

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We have studied the equilibration shown in eq. [3] of 4,4′-dimethoxytrityl alcohol in aqueous perchloric and nitric acids containing low proportions of acetonitrile using stopped-flow kinetics techniques. The rate constants for the overall progress to equilibrium, k obs , have been resolved into forward and reverse components using the equilibrium UV absorbance and a value for the molar absorptivity of the 4,4′-dimethoxytrityl carbenium ion determined in concentrated aqueous perchloric acid. The forward reaction (rate constant k f ) is first order in both the alcohol and the acid concentrations; the reverse reaction (rate constant k r ) is pseudo first order with respect to the carbocation. At constant hydronium ion concentration, the forward rate constant increases linearly with the concentration of electrolyte, whereas the reverse rate constant decreases. These effects depend upon the nature of the anion, but not the cation, and are not ionic strength effects. At constant anion concentrations, k f in both acids, and k r in perchloric acid, are independent of hydronium ion concentration; however, k r decreases with increasing hydronium ion concentration at constant nitrate concentration. At nonconstant ionic strength, changes in k f and k r observed in increasing concentrations of perchloric acid are attributable wholly to changes in perchlorate concentration. A mechanism is proposed which involves pre-equilibrium protonation of the alcohol, heterolysis of the protonated alcohol to give a 4,4′-dimethoxytrityl carbenium ion -water ion-molecule pair, then conversion of this into a dissociated carbenium ion in equilibrium with ion pairs. To account for the strong effects of perchlorate and nitrate upon the forward rate constants, it is proposed that these anions provide additional reaction channels from the ion-molecule pair. However, we find no evidence of acid catalysis in the reaction of the ion-molecule pair (in contrast to our finding for the reaction of the corresponding ion-molecule pair formed from dimethoxytritylamine in acidic media). Some of the elementary rate and equilibrium constants of the proposed mechanism have been evaluated.

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Section: Discussionmentioning

confidence: 99%

“…[11] gives eq. [13] where K 2 = k 2 /k -2 and values for K 1 K 2 k 3 and K 1 k 4 obtained by linear regression of k f against…”

Section: Discussionmentioning

confidence: 99%

Section: Influence Of Hydronium Ion Concentrationmentioning

confidence: 99%

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The 4,4'-dimethoxytrityl carbenium ion by ionization of 4,4'-dimethoxytrityl alcohol in acetonitrile - aqueous perchloric and nitric acids containing electrolytes: kinetics, equilibria, and ion-pair formation

Crugeiras¹,

Maskill²

1999

Can. J. Chem.

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“…123 Later on, it was realised that free ions could also be generated upon direct excitation into the charge-transfer band of donor-acceptor complexes in polar solvents, however, with a substantially smaller yield. [124][125][126][127][128] This difference was explained by the existence of different types of ion pairs, depending on the excitation scheme, bimolecular CS quenching yielding socalled loose ion pairs (LIPs), and charge-transfer excitation resulting in tight ion pairs (TIPs). 129,130 Many other denominations can be found in the literature for LIPs, such as solventshared or solvent-separated ion pairs, as well as for TIPs, like intimate or contact ion pairs.…”

Section: Ion Pairsmentioning

confidence: 99%

Bimolecular photoinduced electron transfer reactions in liquids under the gaze of ultrafast spectroscopy

Rosspeintner

Vauthey

2014

Phys. Chem. Chem. Phys.

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Because of their key role in many areas of science and technology, bimolecular photoinduced electron transfer reactions have been intensively studied over the past five decades. Despite this, several important questions, such as the absence of the Marcus inverted region or the structure of the primary reaction product, have only recently been solved while others still remain unanswered. Ultrafast spectroscopy has proven to be extremely powerful to monitor the entire electron transfer process and to access, with the help of state-of-the-art theoretical models of diffusion-assisted reactions, crucial information like e.g. the intrinsic charge separation dynamics beyond the diffusion limit. Additionally, extension of these experimental techniques to other spectral regions than the UV-visible, such as the infrared, has given a totally new insight into the nature, the structure and the dynamics of the key reaction intermediates, like exciplexes and ions pairs. In this perspective, we highlight these recent progresses and discuss several aspects that still need to be addressed before a thorough understanding of these processes can be attained.

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“…Electron and energy transfer processes between donor-acceptor components not only provide useful methodologies for exploring reaction mechanisms in DNA [1,2] but are also the most common deactivation pathways for the excited state of many organic and inorganic systems [3][4][5]. Owing to the availability of versatile derivatives of synthetic chromophores and their good lightharvesting properties, there has been great interest in optimizing and controlling desirable features of a simple donor-acceptor molecular system for photoinduced charge transfer and separation, which are prerequisites for solar photovoltaic cell applications [6].…”

Section: Introductionmentioning

confidence: 99%

Photoinduced energy and electron transfer in rubrene–benzoquinone and rubrene–porphyrin systems

Khan¹,

Abbas²,

Aly³

et al. 2014

Chemical Physics Letters

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Direct observation of ion-pair dynamics

Cited by 80 publications

References 3 publications

The 4,4'-dimethoxytrityl carbenium ion by ionization of 4,4'-dimethoxytrityl alcohol in acetonitrile - aqueous perchloric and nitric acids containing electrolytes: kinetics, equilibria, and ion-pair formation

The 4,4'-dimethoxytrityl carbenium ion by ionization of 4,4'-dimethoxytrityl alcohol in acetonitrile - aqueous perchloric and nitric acids containing electrolytes: kinetics, equilibria, and ion-pair formation

Bimolecular photoinduced electron transfer reactions in liquids under the gaze of ultrafast spectroscopy

Photoinduced energy and electron transfer in rubrene–benzoquinone and rubrene–porphyrin systems

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