Transient absorption and two-step laser excitation fluorescence spectra of the excited-state and ground-state proton transfer in 7-hydroxyquinoline

Itoh, Michiya; Adachi, Takayuki; Tokumura, Kunihiro

doi:10.1021/ja00352a047

Cited by 40 publications

(39 citation statements)

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“…For e.g., the relay proton transfer of 7-hydroxyquinoline and 3-hydroxyxanthone involves cyclic networks of two and three solvent molecules, respectively. 58,59 Therefore, to determine the number of methanol molecules acting as a bridge connecting the 'NH' group and pyridyl nitrogen in the relay transfer, the fluorescence characteristics are investigated in the acetonitrile-methanol mixture. DMAPIP-c emits a single emission at 390 nm in acetonitrile and is consistent with the earlier work.…”

Section: Binary Solvent Mixture and Stoichiometrymentioning

confidence: 99%

Relay proton transfer triggered twisted intramolecular charge transfer

Behera

Krishnamoorthy

2015

Photochem Photobiol Sci

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The mechanism for the dual emission of 2-(4'-N,N-dimethylaminophenyl)imidazo[4,5-c]pyridine (DMAPIP-c) in protic solvents was investigated by synthesizing and studying its analogues. Theoretical calculations were carried out to corroborate the experimental findings. The deprotonation studies suggest that the enhancement in the TICT emission of anionic forms of DMAPIP-c is limited to a protic environment. The spectral characteristics of DMAPIP-c were also studied in a methanol-acetonitrile binary solvent mixture. Unlike DMAPIP-c, the methyl derivatives do not emit dual fluorescence in protic solvents. The relative intensity of the TICT emission (with respect to that of normal emission) rises with the methanol amount in the acetonitrile-methanol binary solvent mixture. The studies also show that a 1:3 hydrogen bonded complex is formed between DMAPIP-c and methanol and it is responsible for the TICT emission. Based on the results a relay proton transfer tiggered TICT emission is proposed. TDDFT calculations were performed to predict the emission energies.

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Section: Binary Solvent Mixture and Stoichiometrymentioning

confidence: 99%

Relay proton transfer triggered twisted intramolecular charge transfer

Behera

Krishnamoorthy

2015

Photochem Photobiol Sci

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“…The study of cation‐assisted proton transfer from water to electronically excited heterocyclic bases was pioneered by Weller 4 who investigated the proton abstraction reaction of excited acridine and 6‐hydroxyquinoline in water. Heterocyclic bases, which are much stronger bases in their first excited singlet state than in their ground electronic state, have been since extensively studied in solution 4–21 …”

Section: Introductionmentioning

confidence: 99%

“…They have found that cations with relatively high charge density (i.e., small or multi‐charged cations such as Li + , Ca 2+ , and Mg 2+ ) considerably accelerate the rate of proton transfer from water to the imine group, and have demonstrated by direct kinetic analysis that water molecules that are strongly interacting with metal cations are more acidic than bulk water. Picosecond fluorescence spectroscopy made it possible to investigate in real‐time the ultrafast proton abstraction dynamics from water by imine protonation of the anionic (phenolate) form of 3‐, 6‐, and 7‐hydroxyquinolines solutions 14–20 …”

Section: Introductionmentioning

confidence: 99%

Cation‐Enhanced Deprotonation of Water by a Strong Photobase

Munitz¹,

Avital²,

Pines³

et al. 2009

Israel Journal of Chemistry

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We have used picosecond fluorescence spectroscopy to study the proton-dissociation dynamics of bulk water and H 2 O molecules solvating Mg 2+ ions in aqueous solutions. We have analyzed the photo-initiated proton-transfer reaction to a photobase 6-aminoquinoline by the Collins-Kimball approach and have modeled the ensuing bimolecular reaction dynamics by the Smoluchowski equation with radiation boundary conditions. We have found the on-contact proton transfer rate to follow the Marcus free-energy relation for proton transfer and estimate by this rate-equilibrium correlation the considerable enhancement in the acidity of the water molecules solvating the Mg 2+ ion. Our findings may be used in the study of metalloenzymes such as carbonic anhydrases (CAs), which catalyze the reversible addition reaction of OHto CO 2 by increasing the reactivity of the zinc-bound water molecules by means of stabilizing the product of water dissociation, the OHanion.

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“…Therefore, the occurrence of excited‐state proton transfer (ESPT), if available, requires the assistance of surrounding solvent molecules . As regards an ‐OH‐type of proton donor, a well‐known case in point is that of 7‐hydroxyquinoline ( 7HQ , see Scheme a), for which the formation of a 2:1 (methanol/ 7HQ ) H‐bonded complex through solvent reorganization is required for ESPT . Studies of ESPT catalyzed by protic solvent molecules may provide a valuable model to mimic the ubiquitous proton‐transfer reactions in biological media …”

Section: Introductionmentioning

confidence: 99%

Catalytic‐Type Excited‐State N−H Proton‐Transfer Reaction in 7‐Aminoquinoline and Its Derivatives

Chang

Liu

et al. 2019

Chemistry A European J

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7‐Aminoquinoline (7AQ) and various amino derivatives thereof (‐NHR) have been strategically designed and synthesized to study their excited‐state proton‐transfer (ESPT) properties. Due to the large separation between the proton donor ‐NHR and the acceptor ‐N‐ site, ESPT in 7AQ derivatives, if available, should proceed under protic solvent catalysis. ESPT is found to be influenced by the acidity of ‐NHR and the basicity of the proton‐acceptor ‐N‐ in the quinoline moiety. The latter is varied by the resonance effect at the quinoline ‐N‐ site induced by the ‐NHR substituent. For those 7AQ derivatives undergoing ESPT, increased quinoline basicity results in a faster rate of ESPT, implying that proton donation from methanol to the quinoline moiety may serve as a key step in the process. Our studies also indicate the existence of an equilibrium between cis and trans arrangements of ‐NHR in terms of its hydrogen‐bond (H‐bond) configuration with methanol, whereby only the cis‐H‐bonded form undergoes methanol‐assisted ESPT. With one exception, the interconversion between cis and trans configurations is much faster than the rate of ESPT, yielding amino‐type (normal form) and imine‐type (proton‐transfer tautomer) emissions with distinct relaxation dynamics.

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Transient absorption and two-step laser excitation fluorescence spectra of the excited-state and ground-state proton transfer in 7-hydroxyquinoline

Cited by 40 publications

References 1 publication

Relay proton transfer triggered twisted intramolecular charge transfer

Relay proton transfer triggered twisted intramolecular charge transfer

Cation‐Enhanced Deprotonation of Water by a Strong Photobase

Catalytic‐Type Excited‐State N−H Proton‐Transfer Reaction in 7‐Aminoquinoline and Its Derivatives

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