Steady-State Spectroscopy to Single Out the Contact Ion Pair in Excited-State Proton Transfer

Grandjean, Alexander; Lustres, J. Luis Pérez; Muth, Stephan; Maus, Daniel; Jung, Gregor

doi:10.1021/acs.jpclett.0c03593

Cited by 8 publications

(23 citation statements)

References 43 publications

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“…This affords polarity‐dependent SE spectra of complex and HBIP. The SE bandshapes match the positions of the SE bands in the TA spectra almost perfectly, which is taken as further confirmation of the solvatochromic analysis performed in our previous publication [30] …”

Section: Discussionsupporting

confidence: 87%

“…The corresponding spectral amplitudes, the DAS, are shown in Figure 6. Remarkably, τ 3 matches the decay time of the deprotonated form in pure acetonitrile: 6.15 ns [30] . Furthermore, its associated amplitude matches the SE bandshape of RO − , indicating that the latter is formed non‐reversibly in the excited‐state.…”

Section: Resultssupporting

confidence: 53%

“…Ideally, proton‐transfer complexes for intermolecular proton transfer must fulfill a series of requirements as high photostability and fluorescence quantum yield, high association constants in the ground state, single complexation sites, high spectral contrast between bound and unbound species and be electrically neutral to favor good solubility in a broad range of solvents. The molecular system presented in our previous publication [30] fulfills these conditions. A pyrene‐based photoacid (ROH, with

p K_{a} = 4.7

and

p K_{a}^{*} = - 2.7

) binds a tri‐n‐octyl‐phosphine oxide (TOPO) in the ground electronic state, see Scheme 2 [30,31] .…”

Section: Introductionmentioning

confidence: 75%

“…The molecular system presented in our previous publication [30] fulfills these conditions. A pyrene‐based photoacid (ROH, with

p K_{a} = 4.7

and

p K_{a}^{*} = - 2.7

) binds a tri‐n‐octyl‐phosphine oxide (TOPO) in the ground electronic state, see Scheme 2 [30,31] . Excited‐state proton transfer occurs along the hydrogen‐bond of the complex.…”

Section: Introductionmentioning

confidence: 75%

“…Remarkably, the SE bandshapes shown in the top panel of Figure 7 were obtained by spectral decomposition and solvatochromic analysis of the stationary fluorescence spectra of the ROH : TOPO complex in an ample number of solvents [30] . This affords polarity‐dependent SE spectra of complex and HBIP.…”

Section: Discussionmentioning

confidence: 93%

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Solvent‐Controlled Intermolecular Proton‐Transfer Follows an Irreversible Eigen‐Weller Model from fs to ns

2021

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Intermolecular Proton Transfer (PT) dynamics can be best studied by optical spectroscopy, which can cover the vast timescale spanned by the process. PT in a hydrogen bonding complex between a pyranine‐based photoacid and a trialkyl‐phosphine oxide is addressed. The photoreaction is traced with the help of femtosecond transient absorption and picosecond‐resolved fluorescence. Characteristic kinetics and spectra of the intervening species are isolated by global analysis and spectral decomposition of time‐resolved fluorescence. It is found that the shared proton shifts towards the phosphine site upon photoexcitation in acetonitrile. The process occurs on the sub‐picosecond timescale, essentially, under solvent control. Despite the ultrafast rate, an equilibrium between the complex and the hydrogen‐bonded ion pair (HBIP) is established. Further reaction steps are delayed to the nanosecond timescale, where formation of the excited deprotonated form is observed. The far‐reaching consistency between the various methods supports an irreversible Eigen‐Weller mechanism in the excited state.

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Section: Discussionsupporting

confidence: 87%

Section: Resultssupporting

confidence: 53%

p K_{a} = 4.7

and

p K_{a}^{*} = - 2.7

) binds a tri‐n‐octyl‐phosphine oxide (TOPO) in the ground electronic state, see Scheme 2 [30,31] .…”

Section: Introductionmentioning

confidence: 75%

“…The molecular system presented in our previous publication [30] fulfills these conditions. A pyrene‐based photoacid (ROH, with

p K_{a} = 4.7

and

p K_{a}^{*} = - 2.7

) binds a tri‐n‐octyl‐phosphine oxide (TOPO) in the ground electronic state, see Scheme 2 [30,31] . Excited‐state proton transfer occurs along the hydrogen‐bond of the complex.…”

Section: Introductionmentioning

confidence: 75%

Section: Discussionmentioning

confidence: 93%

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Solvent‐Controlled Intermolecular Proton‐Transfer Follows an Irreversible Eigen‐Weller Model from fs to ns

2021

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Excited‐State Proton Transfer Dynamics of a Super‐Photoacid in Acetone‐Water Mixtures

et al. 2022

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Super‐photoacids, that is, photoacids with a negative pKnormala value in the electronically excited state, can trigger an excited‐state proton transfer (ESPT) to the solvent. For the neutral pyranine‐derived super‐photoacid studied here, even indications for ESPT in acetoneous solution are reported. The characteristics of ESPT in this environment, that is, which intermediates exist and what the impact of cosolvents is, remain unsettled though. In this work, we study ESPT in acetone‐water mixtures by steady‐state and time‐resolved fluorescence spectroscopy. Various effects are observed: First, the addition of water supports the formation of a hydrogen‐bonded ground‐state complex comprising one water molecule and the photoacid, whose excitation triggers the formation of a hydrogen‐bonded ion pair on a sub‐ns time scale. Second, water has an overall accelerating effect on the fluorescence dynamics of the involved emitting species, whose contributions are disentangled in a global analysis scheme, enabling the identification of emission from the free photoacid, a photoacid‐water complex, a hydrogen‐bonded ion pair, and the deprotonated photoacid. At least two water molecules are necessary for ESPT in the environment. Third, additional acidification thwarts an efficient ground‐state complex formation of the photoacid and water. However, upon excitation, complexation may occur on a timescale faster than the photoacid's excited‐state lifetime, so that emission from a nascent complex emerges.

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Ultrafast transient absorption and solvation of a super-photoacid in acetoneous environments

Knorr

Sülzner

Geissler

et al. 2022

Photochem Photobiol Sci

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The phenomenon of photoacidity, i.e., an increase in acidity by several orders of magnitude upon electronic excitation, is frequently encountered in aromatic alcohols capable of transferring a proton to a suitable acceptor. A promising new class of neutral super-photoacids based on pyranine derivatives has been shown to exhibit pronounced solvatochromic effects. To disclose the underlying mechanisms contributing to excited-state proton transfer (ESPT) and the temporal characteristics of solvation and ESPT, we scrutinize the associated ultrafast dynamics of the strongest photoacid of this class, namely tris(1,1,1,3,3,3-hexafluoropropan-2-yl)8-hydroxypyrene-1,3,6-trisulfonate, in acetoneous environment, thereby finding experimental evidence for ESPT even under these adverse conditions for proton transfer. Juxtaposing results from time-correlated single-photon counting and femtosecond transient absorption measurements combined with a complete decomposition of all signal components, i.e., absorption of ground and excited states as well as stimulated emission, we disclose dynamics of solvation, rotational diffusion, and radiative relaxation processes in acetone and identify the relevant steps of ESPT along with the associated time scales. Graphical abstract

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Steady-State Spectroscopy to Single Out the Contact Ion Pair in Excited-State Proton Transfer

Cited by 8 publications

References 43 publications

Solvent‐Controlled Intermolecular Proton‐Transfer Follows an Irreversible Eigen‐Weller Model from fs to ns

Solvent‐Controlled Intermolecular Proton‐Transfer Follows an Irreversible Eigen‐Weller Model from fs to ns

Excited‐State Proton Transfer Dynamics of a Super‐Photoacid in Acetone‐Water Mixtures

Ultrafast transient absorption and solvation of a super-photoacid in acetoneous environments

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