Matrix-isolation studies of 7-hydroxyquinoline. 3. Deuterium-isotope and xenon matrix effects

Lavin, Anita; Collins, Susan

doi:10.1021/j100153a031

Cited by 26 publications

(17 citation statements)

References 2 publications

(2 reference statements)

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“…4,5 While the ground-state tautomers (T) of ESIPT systems are often reasonably assumed to be unstable (i.e., with no ground-state local minimum at the equilibrium nuclear configuration of the excited-state T*), nevertheless a few stable ground-state tautomers of ESIPT systems have been observed or inferred. [6][7][8][9][10][11][12][13][14] It is evident that the polarity and H-bonding strength of solvents affect the stabilization of ground-state tautomers. Recently 15,16 Bisht et al interpreted the pressureinduced increase of the emission intensity of salicylic acid in nonpolar methylcyclohexane as partly due to increased formation of the ground-state tautomer with pressure.…”

Section: Introductionmentioning

confidence: 99%

Ground-State Proton-Transfer Tautomer of the Salicylate Anion

et al. 1999

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Solutions of sodium salicylate in anhydrous polar solvents exhibit a weak, temperature-dependent absorption band (λ max ≈ 325 nm) lying in the Stokes gap between the main absorption (296 nm) and the fluorescence band (396 nm, acetonitrile). This weak, longer wavelength absorption band is hardly observable in aqueous solution, but its intensity increases with temperature and increases with polarity in anhydrous organic solvents in the order of ethanol < acetonitrile < dimethyl sulfoxide at room temperature. After correction for solvent thermal contraction, the temperature-dependent absorption spectrum of salicylate in acetonitrile solutions reveals a clear isosbestic point ( 310 ) 2000 M -1 cm -1 ) characteristic of an equilibrium between two salicylate species with band-maximum extinction coefficients of 325 ) 3400 M -1 cm -1 and 296 ) 3586 M -1 cm -1 . In acetonitrile at room temperature (298 K) the concentration equilibrium constant (minor/major) for the interconversion reaction between the two species is K 298 ) 0.11, with ∆H ) 1.6 kcal mol -1 and ∆S ) 0.97 cal‚mol -1 K -1 . The fluorescence lifetime (4.8 ns in acetonitrile) and the shape of the fluorescence spectrum are independent of excitation wavelength. The fluorescence quantum yield for excitation in the long-wavelength shoulder (340 nm) is approximately 60% larger than the yield for excitation in the main band at 296 nm ( 340 ) 0.29, 296 ) 0.18) in acetonitrile at room temperature. These results are consistent with assignment of the shoulder band to the proton-transfer tautomer of the salicylate anion. Electronic structure calculations support assignment of the 325 nm absorption band to the ground-state tautomer (phenoxide anion form) of the salicylate anion. Absorption transition moments for both the normal and tautomer forms are parallel to the emission transition moment, are electronically allowed, and are consistent with 1 L b assignment for both absorbing and emitting transitions. The static dipole moments are in the order of µ(N*) g µ(N) > µ(T*) > µ(T) for the normal (N) and tautomer (T) ground and electronic excited states.

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Section: Introductionmentioning

confidence: 99%

Ground-State Proton-Transfer Tautomer of the Salicylate Anion

et al. 1999

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“…The two tautomers of 7-hydroxyquinoline as well as the anion 7Q À and the cation 7H 2 Q þ have been extensively characterized by absorption and fluorescence spectroscopy in non-polar, polar and protic solvents [59][60][61][62][63][64][65][66][67][68][69][70]. 7HQ emits in the 370-390 nm range, depending on the solvent, while 7KQ emits in the 525-580 nm range, strongly Stokes shifted relative to 7HQ.…”

Section: Techniques Usedmentioning

confidence: 99%

Controlling Excited‐State H‐Atom Transfer along Hydrogen‐Bonded Wires

Manca

Tanner

Leutwyler

2010

Hydrogen Bonding and Transfer in the Excited State

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Hydrogen-bonded wires are involved in a large variety of chemical and biological processes [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. The main reaction associated with hydrogen bonds is proton or H-atom transfer, in which a charge accompanies the transferring proton. A topic of specific interest is proton transport through transmembrane ion channels ('proton wires'), because many transmembrane proteins create, control and use the proton gradient across biological membranes. Hydrogen-bonded wires of water molecules have been identified in numerous membrane-spanning proteins, such as bacteriorhodopsin [17][18][19][20][21][22], the bacterial photosynthetic reaction centre of Rhodobacter sphaeroides [23], the transmembrane channel formed by gramicidin [24][25][26], cytochrome oxidase [27] and other voltage-gated proton channels [28]. The enzymes carbonic anhydrase [29,30] and alcohol dehydrogenase [30] also contain proton relays along chains of water molecules embedded in the interior of the protein. Recently, hydrogen-bonded ammonia wires have been detected in ammonia/ammonium transporter (Amt) transmembrane proteins, which are essential for nitrogen metabolism in all species [31,32]. The translocation mechanisms along these 'proton wires' have become fields of intense theoretical study [5-8, 24-26, 29, 30, 33, 34]. Most of the time, the assumed mechanism is Grotthuss type, after the inventor (1806) of the process. The modern version of the Grotthuss mechanism consists of successive transfers of an excess proton along a hydrogen-bonded wire. These transfers require sequences of reorientation of the wire molecules, which constitutes the rate-limiting step of the mechanism [35]. The excess proton diffuses through a hydrogen bond network via the formation/breaking of covalent bonds, as shown schematically in

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“…The analogous fluorescence appears in rare-gas matrices following excitation of the ground state keto form at 23 800-25 000 cm Ϫ1 . [32][33][34][35] In basic (pHϾ9) aqueous solutions, excitation of the 7HQ Ϫ absorption at 25 910 cm Ϫ1 leads to a fluorescence band with max ϭ20 620 cm Ϫ1 , arising from emission of the 7Q Ϫ anion, and the yellow 7KQ* fluorescence is no longer observed. 26…”

Section: A Absorption and Fluorescence Spectra Of 7-hydroxyquinolinementioning

confidence: 99%

“…S 1 ←S 0 electronic excitation of 7HQ renders the -O-H group more acidic and the N atom more basic, leading to an ESPT reaction in bulk protic solvents. [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] In gasphase ammonia solvent clusters, laser excitation of 7HQ to the S 1 state can trigger the injection of the proton into the cluster, followed by a series of proton transfers along the ammonia wire until the aromatic molecule is reprotonated at the quinolinic N atom, equivalent to a cluster-mediated enol→keto tautomerization. 23,25 Ab initio calculations using Hartree-Fock 24 and density functional 25 ͑DFT͒ methods provide a picture of a step-by-step PT along ammonia wire clusters held at both ends by the 7HQ scaffold, and predict cluster-size dependent effects on the ground state PT.…”

Section: Introductionmentioning

confidence: 99%

“…[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] Both spectroscopic and laser kinetic measurements have been interpreted in terms of models for excited state enol→keto tautomerization involving PT reactions along a hydrogen bonded chain of two or three solvent molecules between the -O-H group and the N atom. [28][29][30][31][32][33][34][35][36][37][38][39][40] The S 0 and S 1 state PT behavior is similar for 6-methyl-7HQ, but different for 8-methyl-7HQ, where the H bonded chain of solvent molecules is believed to be interrupted. 36 A recent review of the ground and excited state photoreactions of 7HQ in bulk solution has been given by Bardez.…”

Section: Introductionmentioning

confidence: 99%

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