Proton Transfer In 3-hydroxyflavone Research Articles

Nonadiabatic excited-state intramolecular proton transfer in 3-hydroxyflavone: S2 state involvement via multi-mode effect.

The excited-state intramolecular proton transfer process in 3-hydroxyflavone is investigated based on the computed structural parameters and energetics of stationary points of vibronically coupled S1-S2 potential energy surfaces. A conical intersection close to the Franck-Condon point on S1 is identified. The minimum energy of the conical intersection is found to be near-degenerate with the equilibrium minimum of S2. Quantum nuclear wavepacket simulations revealed a small population transfer from the "bright" S1 to "dark" S2 on a time scale shorter than the O-H stretching vibrational period. Such a nonadiabatic transition opens up the possibility of new photophysical and photochemical pathways, including the proton transfer via S2.

Different types of hydrogen-bonded complexes would accelerate or delay the excited state proton transfer in 3-hydroxyflavone

3-hydroxyflavone (3HF) has been found dual emission in polar and protic solvents for many years. The excited state proton transfer (ESPT) is the key to control the dual emissions of 3HF. We found the ESPT rate of 3HF in hexane is faster than in acetonitrile because of the lower ESPT energy barrier in hexane. Hence, it was found there are two ESPT rates in methanol, one is faster than in hexane, and the other is slower than in acetonitrile. Two solvent-solute hydrogen bonded complexes (I and II) response to the two ESPT rates. The energy barrier of ESPT was found the lowest (1.324 kcal/mol) in Complex I, corresponded to the shortest ESPT time constant (<0.09 ps). In Complex II, the ESPT time constant is the longest (21.97 ps) with the highest ESPT energy barrier (3.865 kcal/mol). Comparing the results of two complexes, we found that intermolecular hydrogen-bonds would accelerate or delay the ESPT of 3HF based on their different types.

Role of solute-solvent hydrogen bonds on the ground state and the excited state proton transfer in 3-hydroxyflavone. A systematic spectrophotometric study.

A detailed account on the photophysics of 3-hydroxyflavone (3HF) in 27 organic solvents is reported. Dual fluorescence of neutral 3HF was observed in protic, polar, and weakly polar solvents, endowed with sufficiently high hydrogen bond accepting and/or donating capabilities. Ground-state solvent-induced 3HF deprotonation was reported in 14 cases. 3HF anion photophysics was investigated, and the deprotonation constant Kdep calculated. Previously reported models (based on solute-solvent intermolecular hydrogen bonds) to explain solvent effects on Excited-State Intramolecular Proton Transfer (ESIPT) and on solvent-induced deprotonation have been re-examined and improved in order to rationalize the observed photophysical behaviour in all the studied solvents. Hydrogen bond donor acidity and hydrogen bond acceptor basicity are shown to be key parameters. The results are discussed in the framework of the use of 3HF as an environment-sensitive fluorescent sensor in several research fields, and as a model system in the study of ESIPT reactions. Solvent effects on 3HF reactivity are also discussed, as the role of the surrounding media on the chemistry of flavonols is an emerging topic in natural product research.

COMMUNICATION: Solvent effects on the energy barrier of excited state proton transfer in 3-hydroxyflavone

COMMUNICATION: Solvent effects on the energy barrier of excited state proton transfer in 3-hydroxyflavone

ChemInform Abstract: Direct Observation of Fast Proton Transfer: Femtosecond Photophysics of 3-Hydroxyflavone

We report the first investigation of the fast excited-state intramolecular proton transfer of 3-hydroxyflavone. Picosecond stimulated emission and transient absorption spectroscopy demonstrate that the tautomer formation can be monitored by 620-nm transient absorption. The excited-state proton transfer was studied at 620 nm with femtosecond time resolution, and determined to be 240±50 fs in a nonpolar solvent environment. The fast excited-state proton transfer in methanol solution, however, was faster than the 125-fs instrument response

Proton transfer in 3-hydroxyflavone: The influence of physical excitation conditions and dynamic quenching

The influence of excitation conditions, temperature, and fluorescence quencher on the properties of 3-hydoxyflavone excited states is considered. Two-band fluorescence spectra of 3-hydroxyflavone formed in excitation by electromagnetic radiation in the region of the S1 and S2 absorption bands over the temperature range 20–80°C were recorded and analyzed. The TEMPO spin quencher was used as an excited state quencher. An analysis of the fluorescence parameters showed that solution heating from room temperature to 60°C increased the rate of proton transfer by 1.24 times at standard excitation into the main absorption band. The rate increased still more rapidly (by 6.9 times) in excitation into the second absorption band. The presence of the quencher caused a decrease in the yields of both fluorescence bands according to the diffusion mechanism and a noticeable growth in the rate of proton transfer. The latter increased by 1.16 times at room temperature and by 1.25 times at 80°C. The corresponding changes were more substantial, especially at elevated temperatures, if the second singlet band was excited. They then amounted to 1.24 and 3.5 times over the same temperature range.

Excited state intramolecular proton transfer in 3-hydroxy flavone and 5-hydroxy flavone: A DFT based comparative study

Potential energy (PE) curves for the intramolecular proton transfer in the ground (GSIPT) and excited (ESIPT) states of 3-hydroxy-flavone (3HF) and 5-hydroxy-flavone (5HF) were studied using DFT/B3LYP (6-31G (d,p)) and TD-DFT/B3LYP (6-31G (d,p)) level of theory respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer for both the compounds. Calculated PE curves of 3HF for the ground and excited singlet states proton transfer process explain its four state laser diagram. Excited states PE calculations support the ESIPT process to both 5HF and 3HF. The difference in ESIPT emission process of 3HF and 5HF have been explained in terms of HOMO and LUMO electron distribution of the enol and keto tautomer of these two compounds.

Effect of temperature and dynamic fluorescence quenching on proton transfer in 3-hydroxyflavone

The effect of temperature and a fluorescence quencher on the properties of the excited states of 3-hydroxyflavone is considered. The absorption spectra and the spectra of dual fluorescence exited by electromagnetic radiation in the region of the S1 absorption band of 3-hydroxyflavone in acetonitrile are measured and analyzed in the temperature range of 20–80°C. The fluorescence lifetimes are also measured at different temperatures. As a quencher of excited states we used the TEMPO spin quencher. The analysis of the fluorescence parameters shows that the heating of the solution to 60°C leads to a considerable (by a factor of 1.24) increase in the proton-transfer rate for the first absorption band. The introduction of a quencher decreases the yield of the two fluorescence bands by the diffusion mechanism and increases the proton-transfer rate with respect to the rate in the pure solvent by a factor of 1.16 at room temperature and 1.65 at T = 80°C.

Dynamic quenching of the dual fluorescence of molecules

Mathematical relations describing the properties of spontaneous steady-state dual fluorescence under conditions of dynamic quenching of excited states by foreign impurities are derived. It is shown that, in the case of a kinetic character of the reaction, the initial form of the dye and its photoproduct are quenched, the intensity ratio of the fluorescence bands of the initial form and the product linearly increasing with the quencher concentration. Analysis performed is applicable to a wide range of photoreactions accompanied by the dual fluorescence (charge transfer, proton transfer, complexation, etc.). The properties of the fluorescence, absorption, and dual fluorescence excitation for 3-hydroxyflavone in acetonitrile under conditions of dynamic quenching by the TEMPO spin quencher with a concentration below 1.25 × 10−2 M are studied. 3-Hydroxyflavone is characterized by the excited-state intramolecular proton transfer and by the fluorescence spectrum consisting of two well-spaced bands. The observed dependences of the intensity of both fluorescence bands on the quencher concentration correspond to the theoretical conclusions. The Stern-Volmer constants calculated from the experimental data on the assumption of diffusion quenching of the excited states are 858 and 1141 M−1 for the normal and tautomeric fluorescence bands, respectively. The experimental results reveal the kinetic character of the excited-state proton transfer in 3-hydroxyflavone in acetonitrile.

Proton Transfer in 3-Hydroxyflavone Studied by High-Resolution 10 K Laser-Excited Shpol'skii Spectroscopy

High-resolution 10 K Shpol'skii spectra of 3-hydroxyflavone (3HF) and its deuterated analogue (3DF) in n-octane and n-octane/octanol mixtures are presented for the first time. In pure n-octane for both 3HF and 3DF, well-resolved excitation and emission spectra were observed, showing fluorescence shifted from 380−460 to 513−550 nm because of excited-state intramolecular proton/deuteron transfer (ESIPT/ESIDT). Compared to those of 3DF, the 3HF excitation and emission bands are much wider because of lifetime-limited homogeneous broadening. Proton transfer is at least a factor of 4 faster than deuteron transfer. From the homogeneous contribution to the total bandwidth of 3HF, the rate constants of ESIPT and ground-state back proton transfer were estimated to be 39 ± 10 and 210 ± 30 fs, respectively. The effect of four octanol additives was investigated. Only for 2-octanol andthough less favorable3-octanol, a new site in the emission spectrum was observed, blue-shifted over 7 and 10 nm, respectively, versus th...

A theoretical analysis of excited state proton transfer in 3-hydroxyflavone. Promoting effect of a low frequency bending mode

The dynamical properties of excited state intramolecular proton transfer in 3-hydroxyflavone have been analyzed on the basis of the time evolution of the quantum states of the two isomeric forms. Potential energy surfaces have been computed at the MNDO/AM1 level. The results shed light on the essential features of the proton transfer mechanism: in particular, the rapidity of the process is to be attributed to the promoting effect of a low frequency bending vibration, which shortens the distance between donor and acceptor atoms.

A picosecond transient absorption study of the intramolecular excited state proton transfer in 3-hydroxyflavone: assignment of the observed bands

The time-resolved transient absorption and gain of 3-hydroxyflavone in ethanol ( T = 300 and 173 K) and MCH ( T = 300 and 198 K) has been investigated. Two absorption bands (A and B) and two gain bands (E 1 and E 2) have been observed. Band A (lying in the 5200 Å spectral region) appears during and just after the excitation step and is assigned to the normal excited form N ★ x Band B (lying in the 6050 Å spectral region) appears after band A and is assigned to the tautomer form T ★. A gain band E 2 (lying at λ=5400 Å) appears at the same time as the B band and is attributed to the T ★→T emission. A gain band E 1 (lying at λ = 5730 Å) appears earlier than the E 2 band. Its origin is discussed and two possible assignments are presented: vibronic progression of the emission spectrum of T ★ or formation of an intermediate species on the proton transfer pathway from N ★ x to T ★.

The ground state tautomer in the excited state relaxation process of 3-hydroxyflavone at room temperature

Very recently, the ground state reverse proton transfer in 3-hydroxyflavone (3-HF) has been reported to take place within 30 ps by picosecond transient absorption spectroscopy by Aartsma and co-workers. Here we present evidence of intervention of a long-lived ground state tautomer involved in the excited state relaxation process of 3-HF by transient absorption and two-step laser excitation fluorescence spectroscopy.

Intramolecular excited-state proton transfer in 3-hydroxyflavone. Hydrogen-bonding solvent perturbations

The phenomenon of excited-state proton transfer in 3-hydroxyflavone is shown to depend sensitively on traces of H-bonding impurities in hydrocarbon solvents. In extremely dry and highly purified hydrocarbon solvents, a unique tautomer yellow-green fluorescence (region I) is observed from 298 to 77 K, independent of solvent temperature and viscosity, in contradiction to the results of previous research. With traces of water present, three regions of fluorescence of 3-hydroxyflavone of 3-hydoxyflavone (2.0 x 10/sup -5/ M in methylcyclohexane (MCH)) can be observed, the tautomer yellow-green fluorescence (maximum at 523 nm) (region I), another green fluorescence (maximum at 497 nm) (region II) attributed to the solute anion, and a blue-violet fluorescence (maximum at 400 nm) (region III) attributed to the normal electromer of 3-hydroflavone. Excitation spectroscopy confirms the presence of a series of ground-state solvates which are correlated with the diverse luminescence behavior observed with water, alcohol, and ether both as trace impurities and as pure solvents. Potential energy curves for the various molecular species studied, and for various solvation modes, are used to reinterpret laser kinetic studies previously published. In particular the reported biexponential normal molecule fluorescence (III) decay, and tautomer fluorescence (I) rise time, are shown to represent a slowmore » solvent-reorganization step from the polysolvated 3-hydroxyflavone and an ultrarapid intrinsic portion-transfer step for the intramolecularly H-bonded 3-hydroxyflavone.« less

Two-step laser excitation fluorescence study of the ground- and excited-state proton transfer in 3-hydroxyflavone and 3-hydroxychromone

Etude de l'excitation en 2 etapes par faisceau laser, de la fluorescence de solution benzenique d'hydroxy-3 flavone et hydroxy-3 chromone. La 1ere excitation induit la formation d'un tautomere T instable, obtenu par transfert de proton a l'etat excite, la 2eme excitation provoque la fluorescence du tautomere T* a l'etat excite

ChemInform Abstract: TRANSIENT ABSORPTION STUDY OF THE INTRAMOLECULAR EXCITED‐STATE AND GROUND‐STATE PROTON TRANSFER IN 3‐HYDROXYFLAVONE AND 3‐HYDROXYCHROMONE

Chemischer InformationsdienstVolume 14, Issue 35 Article ChemInform Abstract: TRANSIENT ABSORPTION STUDY OF THE INTRAMOLECULAR EXCITED-STATE AND GROUND-STATE PROTON TRANSFER IN 3-HYDROXYFLAVONE AND 3-HYDROXYCHROMONE M. ITOH, M. ITOHSearch for more papers by this authorY. TANIMOTO, Y. TANIMOTOSearch for more papers by this authorK. TOKUMURA, K. TOKUMURASearch for more papers by this author M. ITOH, M. ITOHSearch for more papers by this authorY. TANIMOTO, Y. TANIMOTOSearch for more papers by this authorK. TOKUMURA, K. TOKUMURASearch for more papers by this author First published: August 30, 1983 https://doi.org/10.1002/chin.198335078AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume14, Issue35August 30, 1983 RelatedInformation

Transient absorption study of the intramolecular excited-state and ground-state proton transfer in 3-hydroxyflavone and 3-hydroxychromone

Transient absorption study of the intramolecular excited-state and ground-state proton transfer in 3-hydroxyflavone and 3-hydroxychromone

ChemInform Abstract: TIME‐RESOLVED AND STEADY‐STATE FLUORESCENCE STUDIES OF THE EXCITED‐STATE PROTON TRANSFER IN 3‐HYDROXYFLAVONE AND 3‐HYDROXYCHROMONE

Chemischer InformationsdienstVolume 13, Issue 44 Physical Organic Chemistry ChemInform Abstract: TIME-RESOLVED AND STEADY-STATE FLUORESCENCE STUDIES OF THE EXCITED-STATE PROTON TRANSFER IN 3-HYDROXYFLAVONE AND 3-HYDROXYCHROMONE M. ITOH, M. ITOHSearch for more papers by this authorK. TOKUMURA, K. TOKUMURASearch for more papers by this authorY. TANIMOTO, Y. TANIMOTOSearch for more papers by this authorY. OKADA, Y. OKADASearch for more papers by this authorH. TAKEUCHI, H. TAKEUCHISearch for more papers by this authorK. OBI, K. OBISearch for more papers by this authorI. TANAKA, I. TANAKASearch for more papers by this author M. ITOH, M. ITOHSearch for more papers by this authorK. TOKUMURA, K. TOKUMURASearch for more papers by this authorY. TANIMOTO, Y. TANIMOTOSearch for more papers by this authorY. OKADA, Y. OKADASearch for more papers by this authorH. TAKEUCHI, H. TAKEUCHISearch for more papers by this authorK. OBI, K. OBISearch for more papers by this authorI. TANAKA, I. TANAKASearch for more papers by this author First published: November 2, 1982 https://doi.org/10.1002/chin.198244055AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume13, Issue44November 2, 1982 RelatedInformation

Time-resolved and steady-state fluorescence studies of the excited-state proton transfer in 3-hydroxyflavone and 3-hydroxychromone

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTime-resolved and steady-state fluorescence studies of the excited-state proton transfer in 3-hydroxyflavone and 3-hydroxychromoneMichiya Itoh, Kunihiro Tokumura, Yoshifumi Tanimoto, Yoko Okada, Hiroshi Takeuchi, Kinichi Obi, and Ikuzo TanakaCite this: J. Am. Chem. Soc. 1982, 104, 15, 4146–4150Publication Date (Print):July 1, 1982Publication History Published online1 May 2002Published inissue 1 July 1982https://doi.org/10.1021/ja00379a017RIGHTS & PERMISSIONSArticle Views392Altmetric-Citations87LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (583 KB) Get e-Alerts Get e-Alerts