Solvent Assisted Photoacidity

Pines, Dina; Pines, Ehud

doi:10.1002/9783527611546.ch12

Cited by 34 publications

(62 citation statements)

References 138 publications

(279 reference statements)

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“…Protonation and deprotonation of organic molecules occur in 10 −10 to 10 −9 s . Thus, one proton can dissociate or attach to a molecule during fluorescence processes in aqueous solutions, because the lifetime of fluorescence is approximately 10 −9 s .…”

Section: Resultsmentioning

confidence: 99%

“…Generally, there are two methods for estimating the pK a value of a compound in an excited state by utilizing the F€ orster cycle. One utilizes the absorption peaks (15), and the other utilizes both the absorption and emission peaks (36). In the former method, the pK a value of the S 1 state, pK Ã a , is estimated by…”

Section: Comparison Of Our Methods and The Methods Based On The F € Orsmentioning

confidence: 99%

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Theoretical Study of Fluorescence Spectra Utilizing the pK_a Values of Acids in Their Excited States

Hiyama

Akiyama

Yamada

et al. 2013

Photochem & Photobiology

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Assignment of the fluorescence spectrum of firefly luciferin in aqueous solutions was achieved by utilizing not only emission energies but also theoretical absorption spectra and relative concentrations as estimated by pKa values. Calculated Gibbs free energies were utilized to estimate pKa values. These pKa values were then corrected by employing the experimental results. It was previously thought that the main peak near 550 nm observed in the experimental fluorescence spectra at all pH values corresponds to emission from the first excited state of the luciferin dianion [Ando et al. (2010) Jpn. J. Appl. Phys. 49, 117002-117008]. However, we found that the peak near 550 nm at low pH corresponds to emission from the first excited state of the phenolate monoanion of luciferin. Furthermore, we found that the causes of the red fluorescence at pH 1-2 are not only the emission from phenol monoanion but also the emission from the protonated species at nitrogen atom in the thiazoline ring of dianion.

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Section: Resultsmentioning

confidence: 99%

Section: Comparison Of Our Methods and The Methods Based On The F € Orsmentioning

confidence: 99%

Theoretical Study of Fluorescence Spectra Utilizing the pK_a Values of Acids in Their Excited States

Hiyama

Akiyama

Yamada

et al. 2013

Photochem & Photobiology

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“…34,35 Thus, Δp K a ∼ 7 for the reaction: H 2 CO 3 is a far stronger acid than is CH 3 NH 3 + . This Δp K a is already past the transition, near Δp K a ∼ 5 16,18,31–33 between activated and activation-less PT. This Δp K a ∼ 7 acidity difference corresponds to a strongly favorable reaction free energy asymmetry ∼ −10 kcal/mol for the PT reaction.…”

Section: Introductionmentioning

confidence: 87%

Reaction Mechanism for Direct Proton Transfer from Carbonic Acid to a Strong Base in Aqueous Solution I: Acid and Base Coordinate and Charge Dynamics

et al. 2016

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Protonation by carbonic acid H2CO3 of the strong base methylamine CH3NH2 in a neutral contact pair in aqueous solution is followed via Car–Parrinello molecular dynamics simulations. Proton transfer (PT) occurs to form an aqueous solvent-stabilized contact ion pair within 100 fs, a fast time scale associated with the compression of the acid–base hydrogen-bond (H-bond), a key reaction coordinate. This rapid barrierless PT is consistent with the carbonic acid-protonated base pKa difference that considerably favors the PT, and supports the view of intact carbonic acid as potentially important proton donor in assorted biological and environmental contexts. The charge redistribution within the H-bonded complex during PT supports a Mulliken picture of charge transfer from the nitrogen base to carbonic acid without altering the transferring hydrogen’s charge from approximately midway between that of a hydrogen atom and that of a proton.

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“…Photoacids and photobases, molecular systems that respectively exhibit a profound increase in acidity or basicity, 23 , 24 are ideal molecular tools to study proton transport dynamics on ultrafast time scales using short pulse laser systems. 25 , 26 Proton dissociation to or proton abstraction from water and alcohol solvents 27 − 34 and photoacid–base neutralization reactions 35 − 40 have been investigated with picosecond time-correlated single photon counting, femtosecond UV–vis and UV–IR pump–probe techniques.…”

Section: Introductionmentioning

confidence: 99%

Switching between Proton Vacancy and Excess Proton Transfer Pathways in the Reaction between 7-Hydroxyquinoline and Formate

et al. 2021

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Bifunctional or amphoteric photoacids simultaneously present donor (acidic) and acceptor (basic) properties making them useful tools to analyze proton transfer reactions. In protic solvents, the proton exchange between the acid and the base is controlled by the acidity or basicity strength and typically occurs on two different pathways known as protolysis and hydrolysis. We report here how the addition of a formate base will alter the relative importance of the possible reaction pathways of the bifunctional photoacid 7-hydroxyquinoline (7HQ), which has been recently understood to predominantly involve a hydroxide/methoxide transport mechanism between the basic proton-accepting quinoline nitrogen site toward the proton-donating OH group with a time constant of 360 ps in deuterated methanol (CD 3 OD). We follow the reaction dynamics by probing the IR-active marker modes of the different charged forms of photoexcited 7HQ, and of formic acid (HCOOD) in CD 3 OD solution. A comparison of the transient IR spectra as a function of formate concentration, and classical molecular dynamics simulations enables us to identify distinct contributions of “tight” (meaning “contact”) and “loose” (i.e., “solvent-separated”) 7HQ–formate reaction pairs in our data. Our results suggest that depending on the orientation of the OH group with respect to the quinoline aromatic ring system, the presence of the formate molecule in a proton relay pathway facilitates a net proton transfer from the proton-donating OH group of 7HQ-N* via the methanol/formate bridge toward the quinoline N site.

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Solvent Assisted Photoacidity

Cited by 34 publications

References 138 publications

Theoretical Study of Fluorescence Spectra Utilizing the pK_a Values of Acids in Their Excited States

Theoretical Study of Fluorescence Spectra Utilizing the pK_a Values of Acids in Their Excited States

Reaction Mechanism for Direct Proton Transfer from Carbonic Acid to a Strong Base in Aqueous Solution I: Acid and Base Coordinate and Charge Dynamics

Switching between Proton Vacancy and Excess Proton Transfer Pathways in the Reaction between 7-Hydroxyquinoline and Formate

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Solvent Assisted Photoacidity

Cited by 34 publications

References 138 publications

Theoretical Study of Fluorescence Spectra Utilizing the pKa Values of Acids in Their Excited States

Theoretical Study of Fluorescence Spectra Utilizing the pKa Values of Acids in Their Excited States

Reaction Mechanism for Direct Proton Transfer from Carbonic Acid to a Strong Base in Aqueous Solution I: Acid and Base Coordinate and Charge Dynamics

Switching between Proton Vacancy and Excess Proton Transfer Pathways in the Reaction between 7-Hydroxyquinoline and Formate

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Theoretical Study of Fluorescence Spectra Utilizing the pK_a Values of Acids in Their Excited States

Theoretical Study of Fluorescence Spectra Utilizing the pK_a Values of Acids in Their Excited States