Propyl acetate/butyronitrile mixture is ideally suited for investigating the effect of dielectric stabilization on (photo)chemical reactions

Verma, Pragya; Rosspeintner, Arnulf; Kumpulainen, Tatu

doi:10.1039/d0ra04525j

Cited by 7 publications

(6 citation statements)

References 66 publications

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“…A different strategy is here followed: optical excitation of a pre‐established hydrogen‐bonded complex between a photoacid and a base should trigger intermolecular proton transfer in a non‐basic solvent. The approach was successfully applied by a number of groups, [19,26–29] demonstrating that such molecular systems are ideally suited to monitor intermolecular proton transfer dynamics. Under optimal conditions, optical spectra of the various intermediates can be determined by global analysis of fluorescence and transient absorption data.…”

Section: Introductionmentioning

confidence: 99%

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: Introductionmentioning

confidence: 99%

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

2021

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“…To fill this gap, a stable hydrogen-bonded photoacid–base complex, more stable than previous systems, is desirable. Such systems − can be exposed to different solvents, i.e., different surroundings, where they act as a reactive probe for the solvent polarity. Thus, the extent of the proton transfer reaction in an optimized PT pair reports about the polarity of the surroundings, which is quantified by the relative emission of the PT reactants and products.…”

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confidence: 99%

“…Furthermore, the spectral shape of CPX and HBIP was determined, which is fundamental to investigate the system by steady-state single-molecule fluorescence spectroscopy. There are a few examples of alternative systems in the literature, − but unfortunately, many of these have only low fluorescence quantum yields and association constants, more than one complexation site (leading to complex mixtures), or comprise charged photoacids with limited solubility in apolar solvents. These limitations have been overcome with the molecular system proposed here.…”

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confidence: 99%

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

Grandjean

Lustres

Muth

et al. 2021

J. Phys. Chem. Lett.

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Despite the outstanding relevance of proton transfer reactions, investigations of the solvent dependence on the elementary step are scarce. We present here a probe system of a pyrene-based photoacid and a phosphine oxide, which forms stable hydrogen-bonded complexes in aprotic solvents of a broad polarity range. By using a photoacid, an excitedstate proton transfer (ESPT) along the hydrogen bond can be triggered by a photon and observed via fluorescence spectroscopy. Two emission bands could be identified and assigned to the complexed photoacid (CPX) and the hydrogen-bonded ion pair (HBIP) by a solvatochromism analysis based on the Lippert−Mataga model. The latter indicates that the difference in the change of the permanent dipole moment of the two species upon excitation is ∼3 D. This implies a displacement of the acidic hydrogen by ∼65 pm, which is in quantitative agreement with a change of the hydrogen bond configuration from O−H

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“…Both analyses of the temperature and nitrile mixture experiments resulted in pre-exponential factors for CS close to the theoretical limit of ≲1 × 10 13 s −1 (from transition-state theory or dynamic fluorescence Stokes shift 76,77 ). The value for ΔG°C S from the fit was equal to that for the 0 → 0 transition.…”

Section: ■ Conclusionmentioning

confidence: 56%

Solvent and Temperature Effects on Photoinduced Proton-Coupled Electron Transfer in the Marcus Inverted Region

et al. 2021

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Concerted proton-coupled electron transfer (PCET) in the Marcus inverted region was recently demonstrated ( Science 2019 , 364 , 471–475). Understanding the requirements for such reactivity is fundamentally important and holds promise as a design principle for solar energy conversion systems. Herein, we investigate the solvent polarity and temperature dependence of photoinduced proton-coupled charge separation (CS) and charge recombination (CR) in anthracene–phenol–pyridine triads: 1 (10-(4-hydroxy-3-(4-methylpyridin-2-yl)benzyl)anthracene-9-carbonitrile) and 2 (10-(4-hydroxy-3-(4-methoxypyridin-2-yl)benzyl)anthracene-9-carbonitrile). Both the CS and CR rate constants increased with increasing polarity in acetonitrile: n -butyronitrile mixtures. The kinetics were semi-quantitatively analyzed where changes in dielectric and refractive index, and thus consequently changes in driving force (−Δ G °) and reorganization energy (λ), were accounted for. The results were further validated by fitting the temperature dependence, from 180 to 298 K, in n -butyronitrile. The analyses support previous computational work where transitions to proton vibrational excited states dominate the CR reaction with a distinct activation free energy (Δ G * CR ∼ 140 meV). However, the solvent continuum model fails to accurately describe the changes in Δ G ° and λ with temperature via changes in dielectric constant and refractive index. Satisfactory modeling was obtained using the results of a molecular solvent model [ J. Phys. Chem. B 1999 , 103 , 9130–9140], which predicts that λ decreases with temperature, opposite to that of the continuum model. To further assess the solvent polarity control in the inverted region, the reactions were studied in toluene. Nonpolar solvents decrease both Δ G ° CR and λ, slowing CR into the nanosecond time regime for 2 in toluene at 298 K. This demonstrates how PCET in the inverted region may be controlled to potentially use proton-coupled CS states for efficient solar fuel production and photoredox catalysis.

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Propyl acetate/butyronitrile mixture is ideally suited for investigating the effect of dielectric stabilization on (photo)chemical reactions

Abstract: Propyl acetate/butyronitrile mixtures allow for controlling the extent and time scale of dielectric stabilization in a predictable manner.

Cited by 7 publications

References 66 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

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

Solvent and Temperature Effects on Photoinduced Proton-Coupled Electron Transfer in the Marcus Inverted Region

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