Rotational Brownian motion of the proton crane operating in a photoinduced long-distance intramolecular proton transfer

Jalink, C. Jojakim; Huizer, A. Herbert; Varma, Cyril A. G. O.

doi:10.1039/ft9928801643

Cited by 15 publications

(19 citation statements)

References 11 publications

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“…The observed broadening provides experimental support for the procedure, introduced in simulations of the photoinduced tautomerization of HMMQ, in which the electron distribution of the excited chromophoric part of the molecule is adapted to the position of the protonated morpholino group. 7,16 As time proceeds the spectrum sharpens gradually, and at t ) 45 ps a narrower band can be seen around 550 nm.…”

Section: B Time Dependence Of the Transient Absorptionsmentioning

confidence: 99%

“…5,10,11 Previous studies revealed how solvents act in the catalysis of the multistep, photoinduced enol-keto tautomerization of HMMQ. 5,[7][8][9][10][11][12] These studies provide reaction schemes (Figure 1) and other useful information concerning the conversion process. Two forms of HMMQ are in the ground state when the solvent contains proton acceptors (S), namely a bare form with an intramolecular H-bond and a complex in which the proton in the intramolecular H-bond is also H-bonded to S. It has been concluded that only the latter exhibits photoinduced enol-keto tautomerization.…”

Section: Introductionmentioning

confidence: 99%

“…Adiabatic excited state intramolecular proton transfer (ESIPT) from the OH group to the morpholino's N atom can be observed in the case of HMMN only when it is dissolved in a polar solvent, , and in the case of HMMQ when it is dissolved in either a nonpolar or a polar solvent. ,− In the case of solutions of HMMQ in polar solvents or in 1,4-dioxane, the first ESIPT step is followed by rotational Brownian motion of the protonated side group, which enables delivery of the proton at the N atom in the quinoline ring and results in formation of the excited keto form of HMMQ. The fluorescence spectrum of HMMN in an alkane consists of a single band, that arises from the excited enol form, with its maximum at 363 nm.…”

Section: Introductionmentioning

confidence: 99%

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Elementary Processes in Photoinduced Proton Transfers in 2-Hydroxy-1-(N-morpholinomethyl)naphthalene and 7-Hydroxy-8-(N-morpholinomethyl)quinoline in Liquid Solutions

2000

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The evolution of a primary excited electronic state of 2-hydroxy-1-(N-morpholinomethyl)naphthalene (HMMN) and 7-hydroxy-8-(N-morpholinomethyl)quinoline (HMMQ) in liquid solutions has been followed with a time resolution of 200 fs by detecting the emerging transient UV-visible absorptions and stimulated emissions. The primary state lies about 7000 cm -1 above the state S 1 . The spectral changes in the case of HMMN in n-hexane are attributed to vibrational relaxation, because intramolecular proton transfer (i.e., formation of the excited zwitterionic form Z*) does not take place and effects due to dielectric polarization of the solvent could be ruled out. A similar vibrational relaxation has been observed in the case of HMMN in tetrahydrofurane. The Z* state of HMMN emerges in tetrahydrofurane, but only from a complex {E*,S} of the excited enol form (E*) and a solvent molecule (S) and certainly not from the vibrationless S 1 state of E*. The transferable proton in {E*,S} is simultaneously involved in an intramolecular and an intermolecular H-bond. HMMN behaves in a similar fashion as in tetrahydrofurane, when the former is dissolved in 1,4-dioxane. In the case of HMMN in acetonitrile, the evolution of triplet states 3 {Z*,S} can be seen in addition to a quasistationary singlet state 1 {Z*,S} 1 . The intersystem crossing from the singlet into the triplet manifold of states proceeds from 1 {Z*,S} states above the vibrationless state 1 {Z*,S} 1 . The triplet state formation is attributed to the weaker intermolecular H-bond involved in the complex {Z*,S} when S ) CH 3 CN. Dielectric polarization of the solvent is of no significance in promoting the intramolecular proton transfer compared to the specific solute-solvent interaction in the complex {E*,S}. The protonated morpholino group in the Z-* form of HMMN is kept fixed by an intramolecular H-bond in all the cases. In the case of HMMQ, only its solution in tetrahydrofurane has been studied. The rate constant for the conversion of the Z* form of HMMQ into the excited keto (K*) form has been determined, as well as the rate constant for the relaxation of the latter into the ground-state keto form (K). The rate constant for the conversion of the form K of HMMQ into the groundstate enol form (through rotational Brownian motion of the protonated morpholino group) has also been determined. Spectral broadening arising from the motion of the protonated morpholino group in the Z* form of HMMQ has been observed in accordance with previous simulations.

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Section: B Time Dependence Of the Transient Absorptionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Elementary Processes in Photoinduced Proton Transfers in 2-Hydroxy-1-(N-morpholinomethyl)naphthalene and 7-Hydroxy-8-(N-morpholinomethyl)quinoline in Liquid Solutions

2000

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“…The relation I = mR2 is used to calculate R. A previously determined experimental value of E,,, will be used. 14 The required values of the molecular parameters are listed in Table 2.…”

Section: Simulated Reaction Dynamicsmentioning

confidence: 99%

Comparison of several frequency-dependent friction models for the description of liquid-phase reaction dynamics

Jalink¹,

Huizer²,

Varma³

1993

Faraday Trans.

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“…Varma and co-workers were the first to demonstrate the proton-craning behavior of this molecule . The proton crane has been studied previously by steady-state fluorescence, time-resolved fluorescence, and transient absorption spectroscopies as well as simulations. − Interestingly, the intermolecular hydrogen-bond breaking that should precede the craning has never been observed. The ground-state retautomerization has also never been observed, as it was thought to occur too fast. , The experimental techniques employed previously are intrinsically not capable of providing a complete picture of the structural changes that occur during the different steps of the photocycle of the proton crane.…”

Section: Introductionmentioning

confidence: 99%

Unraveling the Mechanism of a Reversible Photoactivated Molecular Proton Crane

et al. 2014

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We study the structural dynamics of the photoactivated molecular proton crane 7-hydroxy-8-(morpholinomethyl)quinoline using femtosecond UV-pump IR-probe spectroscopy. Upon electronic excitation, a proton is transferred from the hydroxy to the amine group located on the rotatable morpholino side group. This morpholino group subsequently delivers the proton to the aromatic quinoline nitrogen by rotation around the C-C bond. Time-resolved vibrational spectroscopy allows us to study this process in unprecedented detail. We find that the transport of the proton involves multiple time scales. Upon photoexcitation, the OH proton is transferred within <300 fs to the morpholino side group. After this, the intramolecular hydrogen bond that locks the crane arm breaks with a time constant of 36 ± 1 ps. Subsequently, the protonated crane arm rotates with a time constant of 334 ± 12 ps to deliver the proton at the quinoline moiety. After the proton crane has returned to its electronic ground state with a time constant 700 ± 22 ps, the proton is transferred back from the quinoline nitrogen to the negatively charged O atom. The time constant of the back rotation is 39.8 ± 0.2 ns, about 200 times slower than the forward proton transfer.

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Rotational Brownian motion of the proton crane operating in a photoinduced long-distance intramolecular proton transfer

Cited by 15 publications

References 11 publications

Elementary Processes in Photoinduced Proton Transfers in 2-Hydroxy-1-(N-morpholinomethyl)naphthalene and 7-Hydroxy-8-(N-morpholinomethyl)quinoline in Liquid Solutions

Elementary Processes in Photoinduced Proton Transfers in 2-Hydroxy-1-(N-morpholinomethyl)naphthalene and 7-Hydroxy-8-(N-morpholinomethyl)quinoline in Liquid Solutions

Comparison of several frequency-dependent friction models for the description of liquid-phase reaction dynamics

Unraveling the Mechanism of a Reversible Photoactivated Molecular Proton Crane

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