The ground-state stabilization of the keto tautomer of the 7-hydroxyquinoline dimer in argon matrices at 10 K

Lavin, Anita; Collins, Susan

doi:10.1016/0009-2614(93)89039-k

Cited by 24 publications

(25 citation statements)

References 5 publications

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“…Emission from T* ( h ν f ) has a characteristically large Stokes gap (>8000 cm -1 ). The nature of the potential energy surface of the ground state at the equilibrium geometry of the excited state of proton-transfer tautomers remains an active area of experimental and theoretical study. , 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. − It is evident that the polarity and H-bonding strength of solvents affect the stabilization of ground-state tautomers. Recently , Bisht et al interpreted the pressure-induced 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 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%

“…We assign it to the ground state 7-keto quinoline tautomer, based on the similarity to the bulk absorption spectra in water or alcohols. 30,[32][33][34][35] On the other hand, the DFT calculations indicate that formation of a solvent-separated ion pair ͑SSIP͒, where the proton hops to the second or third ammonia molecule along the ammonia wire, but does not reach the quinoline N, is another possibility. 25…”

Section: Cluster Spectramentioning

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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Ground- and excited state proton transfer and tautomerization in 7-hydroxyquinoline⋅(NH3)n clusters: Spectroscopic and time resolved investigations

Bach

Tanner

Manca

et al. 2003

The Journal of Chemical Physics

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Diversity of excited state deactivation paths in heteroazaaromatics with multiple intermolecular hydrogen bonds

Dobkowski

Herbich

Galievsky

et al. 1998

Ber Bunsenges Phys Chem

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Transient absorption and luminescence studies were performed for several heteroazaaromatic molecules which possess both hydrogen bonding donor and acceptor groups, and which are capable of forming cyclic, double intermolecular hydrogen bonds. In protic solvents, these systems exhibit complex photophysics, manifested by a strong quenching of the fluorescence. In dipyrido[2,3‐a:3′,2′‐i]carbazole and 7,8,9,10‐tetrahydropyri‐do[2,3‐a]carbazole, photoinduced double proton transfer is observed in the first excited singlet state, leading to tautomeric species which emit strongly Stokes‐shifted fluorescence. The large and temperature‐independent rate of this reaction is observed for the case in which a cyclic complex with an alcohol molecule is formed already in the ground state. Another excited state depopulation channel, internal conversion caused by proton movement in the cyclic complex, is observed in alcohol solutions of 2‐(2′‐pyridyl)‐indoles and pyrido[2,3‐a]carbazole. In these cases, formation of cyclic, doubly hydrogen‐bonded structures occurs in the excited state and involves solvent rearrangement. The rate of this process changes with solvent viscosity and becomes negligible at low temperatures, when the viscosity is high. Fast internal conversion has also been observed in hydrogen‐bonded complexes with azaaromatic bases. Its mechanism can be explained by intermolecular charge transfer interactions. In alcohol solutions of 2‐(2′‐pyridyl)indoles, transient absorption results point to yet another channel of excited state deactivation – photoionization, occurring faster than S1 decay.

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The ground-state stabilization of the keto tautomer of the 7-hydroxyquinoline dimer in argon matrices at 10 K

Cited by 24 publications

References 5 publications

Ground-State Proton-Transfer Tautomer of the Salicylate Anion

Ground-State Proton-Transfer Tautomer of the Salicylate Anion

Ground- and excited state proton transfer and tautomerization in 7-hydroxyquinoline⋅(NH3)n clusters: Spectroscopic and time resolved investigations

Diversity of excited state deactivation paths in heteroazaaromatics with multiple intermolecular hydrogen bonds

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