juan carlos del valle - Academia.edu (original) (raw)
Papers by juan carlos del valle
Angewandte Chemie International Edition, 2014
Journal of Luminescence, 1996
The photophysical behaviour of 2-(2′-hydroxyphenyl) perimidine (6), which possesses a strong intr... more The photophysical behaviour of 2-(2′-hydroxyphenyl) perimidine (6), which possesses a strong intramolecular hydrogen bond is evidenced as due to the non-transferred enol form. This compound is highly stable to light, with a photodegradative quantum yield in ...
Chemical Physics, 2006
The photophysics of the 5-hydroxyflavone (5HF) molecule has been revised. Conversely to what has ... more The photophysics of the 5-hydroxyflavone (5HF) molecule has been revised. Conversely to what has been hitherto reported, the proton-transfer fluorescence of 5HF has been recorded under xenon lamp excitation in cyclohexane, hexane, ethanol, ethyl ether, 2-methyl-2-propanol, and dimethylsulfoxide at room temperature. The 5HF fluorescence spectra only exhibit one emission band centered at ca. 700 nm. A small photoreaction quantum yield of 10-5-10-6 denotes the great photostability exemplified by 5HF in hydrocarbon solvent, ethanol, and dimethylsulfoxide. This great photostability is predominantly explained owing to an internal conversion process from the first excited singlet state 1(π,π*)1 (S1), which has a repulsive (proton-transfer) potential energy curve with respect to the stretching of the OH bond and only one energy minimum for the proton-transfer tautomer. The S1'-S0' energy gap proves to be small because of important modifications found in the molecular geometry of 5HF upon photoexcitation. A computational strategy, based upon theoretical calculations at the B3LYP density functional theory (DFT) and time-dependent DFT levels, supports the experimental spectroscopic evidence. Also an abnormal singlet-triplet splitting for a π,π* configuration has been found in 5HF.
The photophysics of the 5-hydroxyflavone (5HF) molecule has been revised. Conversely to what has ... more The photophysics of the 5-hydroxyflavone (5HF) molecule has been revised. Conversely to what has been hitherto reported, the proton-transfer fluorescence of 5HF has been recorded under xenon lamp excitation in cyclohexane, hexane, ethanol, ethyl ether, 2-methyl-2-propanol, and dimethylsulfoxide at room temperature. The 5HF fluorescence spectra only exhibit one emission band centered at ca. 700 nm. A small photoreaction quantum yield of 10(-5)-10(-6) denotes the great photostability exemplified by 5HF in hydrocarbon solvent, ethanol, and dimethylsulfoxide. This great photostability is predominantly explained owing to an internal conversion process from the first excited singlet state 1(pi,pi*)1 (S1), which has a repulsive (proton-transfer) potential energy curve with respect to the stretching of the OH bond and only one energy minimum for the proton-transfer tautomer. The S1'-S0' energy gap proves to be small because of important modifications found in the molecular geometry of 5HF upon photoexcitation. A computational strategy, based upon theoretical calculations at the B3LYP density functional theory (DFT) and time-dependent DFT levels, supports the experimental spectroscopic evidence. Also an abnormal singlet-triplet splitting for a pi,pi* configuration has been found in 5HF.
The Journal of Physical Chemistry, 1995
... Alexander Sytnik* and Juan Carlos Del Valle? Institute of Molecular Biophysics, Florida State... more ... Alexander Sytnik* and Juan Carlos Del Valle? Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306-301 5 Received: April 13, 1995; In Final Form: June 12, 1999 ... J.; Perez, P.; Fabero, F.; Wilshire, JFK; Claramunt, R. M.; Elguero, J. J. Am. Chem. ...
International Journal of Quantum Chemistry, 1999
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![Research paper thumbnail of Understanding the solvatochromism of 10-hydroxybenzo[h]quinoline. An appraisal of a polarity calibrator](https://attachments.academia-assets.com/48934043/thumbnails/1.jpg)
](Chemical Physics, 2001
The solvatochromism of the 10-hydroxybenzo[h]quinoline molecule (HBQ) has been investigated for t... more The solvatochromism of the 10-hydroxybenzo[h]quinoline molecule (HBQ) has been investigated for the S 0→S 1 absorption of the normal tautomer, and for the S 1'→S 0' fluorescence emission of the proton-transfer (PT) tautomer. The wavelength shifts of the first absorption band depend principally on polarity of the solvent used with a minor contribution of acidity, contrary to the fluorescence band wavelength shifts, which exhibit a greater dependence on acidity than on polarity. These observations preclude the use of HBQ for probing polarity in cavities of biopolymers. Theoretical calculations show that the local minimum of electrostatic potential ( Vmin) which is found at the carbonyl oxygen center in the S 1' state of the PT tautomer is much deeper than that Vmin located at the hydroxy oxygen center in the S 1 state of the normal tautomer. This observation is interpreted as a significant increase in basicity of the carbonyl oxygen center, this being approximately twice more basic than the hydroxy oxygen center for the first singlet excited electronic state. Therefore, the oxygen center is the most subjected to be perturbed by solvent acidity. The steps followed in this paper for analyzing the response of HBQ to solvent effects can be applied to any molecular system to be used for probing polarity of the environment (e.g., in biopolymers).
Proceedings of The National Academy of Sciences, 1999
The experimental and theoretical bases for a synchronous or concerted double-proton transfer in c... more The experimental and theoretical bases for a synchronous or concerted double-proton transfer in centrosymmetric H-bonded electronically excited molecular dimers are presented. The prototype model is the 7-azaindole dimer. New research offers confirmation of a concerted mechanism for excited-state biprotonic transfer. Recent femtosecond photoionization and coulombic explosion techniques have given rise to time-of-f light MS observations suggesting sequential two-step biprotonic transfer for the same dimer. We interpret the overall species observed in the time-of-f light experiments as explicable without conf lict with the concerted mechanism of proton transfer.
International Journal of Quantum Chemistry, 1999
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International Journal of Quantum Chemistry, 2000
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Journal of Physical Chemistry A, 1997
... David Gormin, Alexander Sytnik, and Michael Kasha*. Institute of Molecular Biophysics and Dep... more ... David Gormin, Alexander Sytnik, and Michael Kasha*. Institute of Molecular Biophysics and Department of Chemistry, Florida State University, Tallahassee, Florida 32306-3015. J. Phys. Chem. A , 1997, 101 (4), pp 672677. DOI ...
Journal of Luminescence, 1997
Photophysical characterization of perimidine 1, 1-methylperimidine 2, 2-phenylperimidine 3, 1-met... more Photophysical characterization of perimidine 1, 1-methylperimidine 2, 2-phenylperimidine 3, 1-methyl-2-phenylperimidine 4, 2-(2'-hydroxyphenyl)perimidine 5, 1-methyl-2-(2'-hydroxyphenyl)perimidine 6, 2-@'-methoxyphenyl)perimidine 7 and 1-methyl-2-(2'-methoxyphenyl)perimidine 8 has been achieved. All derivatives exhibit a high photostability against the UV light with small photochemical quantum yields 4, in the range of 1O-5-1O-6, implying that non-radiative processes different from the excited state intramolecular proton transfer (ESIPT) mechanism are responsible for their photophysics.
Journal of Organic Chemistry, 1995
Two new families of compounds, the 3(5)-(1'-hydroxy-2'-naphthyl)pyrazoles (a series) and the 3(5)... more Two new families of compounds, the 3(5)-(1'-hydroxy-2'-naphthyl)pyrazoles (a series) and the 3(5)-(2'-hydroxy-l'-naphthyl)pyrazoles (b series), have been synthesized and fully characterized. The use of NMR (lH and I3C) and W (absorption and emission) spectroscopies in different solvents led us to determine the major tautomers, the coplanarity of both rings (naphthyl and pyrazolyl) if present, and the existence of hydrogen bonds. The photostability of a representative set of such derivatives was also determined, showing that the existence of a n intramolecular hydrogen bond (IMHB) is not a n essential condition for providing W stability. Moreover when such an IMHB is present in the molecule, the photostability is not dependent on whether the proton is transferred or not. Abstract published in Advance ACS Abstracts, May 1, 1995. (1) For part 3, see: Catalln, J.; del Valle, J. C.; Claramunt, R. M.; Sanz, D.; Dotor, J. Chem. Phys. Lett. Submitted. (2) Catalln, J.; Fabero, F.; Claramunt, R. M.; Santa Maria, M. D.; Foces-Foces, M. C.; Hernlndez-Cano, F.; Martinez-Ripoll, M.; Elguero, J.; Sastre, R. J . Am. Chem. SOC. 1992, 114, 5039.
Proceedings of The National Academy of Sciences, 2002
A mechanism is proposed for the formation in gas phase, during a short time, of the delicately sy... more A mechanism is proposed for the formation in gas phase, during a short time, of the delicately symmetrical coplanar C2h classic 7-azaindole (7AI) doubly hydrogen-bonded dimer. Of the five card-pack or otherwise random geometry structures most likely to be formed in the supersonic jet expansion molecular beam, none would be an obvious precursor to the C2h dimer. One unstable dimer with dipole-dipole, van der Waals, and plane-to-plane hydrogen bonding is shown to be capable of unhinging about the hydrogen-bond pair as an axis, from 0° to 90° to 180°, yielding a deep minimum for the C2h structure with its delicate geometry and symmetry. This relaxation mechanism is feasible in the 3-μs interval between the nozzle escape and the first laser pulse interception of the molecular beam. In the second part of the paper four published mechanisms are compared for concerted vs. two-step biprotonic phototransfer for the 7AI dimers. The dependence of the latter two models on H-atom instead of proton-transfer as an intermediate step negates the mechanism in a singlet (,*) electronic state by the valency repulsion, in the 3-electron orbital that would be generated. The concerted mechanism for biprotonic phototransfer is reaffirmed by the analysis of the quantum mechanical conditions set on the biprotonic transfer in the photo-excited molecular 7AI pair.
Journal of Physical Chemistry A, 2008
Methylation at the 1N position of 2-phenylimidazole provides the shortest wavelength for a liquid... more Methylation at the 1N position of 2-phenylimidazole provides the shortest wavelength for a liquid-state laser dye reported to date; that is, the 1-methyl-2-phenylimidazole molecule in cyclohexane solution yields amplified spontaneous emission (ASE) with a peak wavelength at 314.5 nm and a constant laser gain value of 5 cm -1 from 310 to 317 nm. Methyl substitution in this case favors the appearance of laser action (owing to a torsion-vibrational mechanism) in cyclohexane as compared with the nonmethylated species which does not exhibit ASE in this solvent. The 2-(2′-hydroxyphenyl)imidazole molecules give rise to ASE with high gain values (ca. 9 cm -1 ) at 450 and 466 nm. The mechanism of population inversion is understood in terms of a vibronic coupling between the hydroxyl stretching motion and the torsional vibration of the phenyl and imidazole rings. The proton-transfer spectroscopy of 2-(2′-hydroxyphenyl)imidazoles is studied in dioxane, cyclohexane, dimethyl sulfoxide, methanol, and water. The greater the acidity of the solvent the greater the disruption of the intramolecular hydrogen bond; solvent acidity is the main parameter which favors formation of the open-form species in the ground electronic state. Methyl substitution at the 1N position favors formation of the open species for 2-hydroxyphenylimidazoles in the ground electronic state, which decreases their own capacity to undergo ASE. Low-temperature absorption spectroscopy confirms aggregation processes for 2-(2′hydroxyphenyl)imidazoles in solution. In accordance with X-ray analyses in the solid phase, these molecules form associations through intermolecular chains of the type NsH · · · O or OsH · · · N.
Journal of The American Chemical Society, 1993
Two new families of compounds, the 3(5)-(1'-hydroxy-2'-naphthyl)pyrazoles (a series) and the 3(5)... more Two new families of compounds, the 3(5)-(1'-hydroxy-2'-naphthyl)pyrazoles (a series) and the 3(5)-(2'-hydroxy-l'-naphthyl)pyrazoles (b series), have been synthesized and fully characterized. The use of NMR (lH and I3C) and W (absorption and emission) spectroscopies in different solvents led us to determine the major tautomers, the coplanarity of both rings (naphthyl and pyrazolyl) if present, and the existence of hydrogen bonds. The photostability of a representative set of such derivatives was also determined, showing that the existence of a n intramolecular hydrogen bond (IMHB) is not a n essential condition for providing W stability. Moreover when such an IMHB is present in the molecule, the photostability is not dependent on whether the proton is transferred or not. Abstract published in Advance ACS Abstracts, May 1, 1995. (1) For part 3, see: Catalln, J.; del Valle, J. C.; Claramunt, R. M.; Sanz, D.; Dotor, J. Chem. Phys. Lett. Submitted. (2) Catalln, J.; Fabero, F.; Claramunt, R. M.; Santa Maria, M. D.; Foces-Foces, M. C.; Hernlndez-Cano, F.; Martinez-Ripoll, M.; Elguero, J.; Sastre, R. J . Am. Chem. SOC. 1992, 114, 5039.
Chemical Physics Letters, 2000
w In this Letter we consider the second laser-pulse time delay experiments of Castleman and co-wo... more w In this Letter we consider the second laser-pulse time delay experiments of Castleman and co-workers D.E. Folmer, L.
Journal of The Chemical Society-perkin Transactions 2, 1995
Journal of Physical Chemistry A, 1999
Chemical Physics Letters, 1996
A spectroscopic study of the fluorescence, amplified spontaneous emission (ASE), and gain spectra... more A spectroscopic study of the fluorescence, amplified spontaneous emission (ASE), and gain spectra is made, testing for UV lasing from several phenyloxazoles. ASE laser spikes occur at 333 and 349 nm for 2-phenylbenzoxazole (PBO), 356 and 374 nm for 2,5-diphenyloxazole (PPO) and 365 and 385 nm for 2-(1-naphthyl)-5-phenyl-l,3,4-oxadiazole (ct-NPD), all in hydrocarbon solution at 298 K. For DPOPOP, 1,4-bis(4-methyl-5-phenyloxazol-2-yl)benzene, the ASE laser spike occurs at 420 nm. The gain coefficients range from 5 to 10 cm-1. Unorthodox features in the ASE spectroscopy serve as a clue to the electronic excitation dynamics of complex composite molecular systems.
Angewandte Chemie International Edition, 2014
Journal of Luminescence, 1996
The photophysical behaviour of 2-(2′-hydroxyphenyl) perimidine (6), which possesses a strong intr... more The photophysical behaviour of 2-(2′-hydroxyphenyl) perimidine (6), which possesses a strong intramolecular hydrogen bond is evidenced as due to the non-transferred enol form. This compound is highly stable to light, with a photodegradative quantum yield in ...
Chemical Physics, 2006
The photophysics of the 5-hydroxyflavone (5HF) molecule has been revised. Conversely to what has ... more The photophysics of the 5-hydroxyflavone (5HF) molecule has been revised. Conversely to what has been hitherto reported, the proton-transfer fluorescence of 5HF has been recorded under xenon lamp excitation in cyclohexane, hexane, ethanol, ethyl ether, 2-methyl-2-propanol, and dimethylsulfoxide at room temperature. The 5HF fluorescence spectra only exhibit one emission band centered at ca. 700 nm. A small photoreaction quantum yield of 10-5-10-6 denotes the great photostability exemplified by 5HF in hydrocarbon solvent, ethanol, and dimethylsulfoxide. This great photostability is predominantly explained owing to an internal conversion process from the first excited singlet state 1(π,π*)1 (S1), which has a repulsive (proton-transfer) potential energy curve with respect to the stretching of the OH bond and only one energy minimum for the proton-transfer tautomer. The S1'-S0' energy gap proves to be small because of important modifications found in the molecular geometry of 5HF upon photoexcitation. A computational strategy, based upon theoretical calculations at the B3LYP density functional theory (DFT) and time-dependent DFT levels, supports the experimental spectroscopic evidence. Also an abnormal singlet-triplet splitting for a π,π* configuration has been found in 5HF.
The photophysics of the 5-hydroxyflavone (5HF) molecule has been revised. Conversely to what has ... more The photophysics of the 5-hydroxyflavone (5HF) molecule has been revised. Conversely to what has been hitherto reported, the proton-transfer fluorescence of 5HF has been recorded under xenon lamp excitation in cyclohexane, hexane, ethanol, ethyl ether, 2-methyl-2-propanol, and dimethylsulfoxide at room temperature. The 5HF fluorescence spectra only exhibit one emission band centered at ca. 700 nm. A small photoreaction quantum yield of 10(-5)-10(-6) denotes the great photostability exemplified by 5HF in hydrocarbon solvent, ethanol, and dimethylsulfoxide. This great photostability is predominantly explained owing to an internal conversion process from the first excited singlet state 1(pi,pi*)1 (S1), which has a repulsive (proton-transfer) potential energy curve with respect to the stretching of the OH bond and only one energy minimum for the proton-transfer tautomer. The S1'-S0' energy gap proves to be small because of important modifications found in the molecular geometry of 5HF upon photoexcitation. A computational strategy, based upon theoretical calculations at the B3LYP density functional theory (DFT) and time-dependent DFT levels, supports the experimental spectroscopic evidence. Also an abnormal singlet-triplet splitting for a pi,pi* configuration has been found in 5HF.
The Journal of Physical Chemistry, 1995
... Alexander Sytnik* and Juan Carlos Del Valle? Institute of Molecular Biophysics, Florida State... more ... Alexander Sytnik* and Juan Carlos Del Valle? Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306-301 5 Received: April 13, 1995; In Final Form: June 12, 1999 ... J.; Perez, P.; Fabero, F.; Wilshire, JFK; Claramunt, R. M.; Elguero, J. J. Am. Chem. ...
International Journal of Quantum Chemistry, 1999
Skip to Main Content. ...
Chemical Physics, 2001
The solvatochromism of the 10-hydroxybenzo[h]quinoline molecule (HBQ) has been investigated for t... more The solvatochromism of the 10-hydroxybenzo[h]quinoline molecule (HBQ) has been investigated for the S 0→S 1 absorption of the normal tautomer, and for the S 1'→S 0' fluorescence emission of the proton-transfer (PT) tautomer. The wavelength shifts of the first absorption band depend principally on polarity of the solvent used with a minor contribution of acidity, contrary to the fluorescence band wavelength shifts, which exhibit a greater dependence on acidity than on polarity. These observations preclude the use of HBQ for probing polarity in cavities of biopolymers. Theoretical calculations show that the local minimum of electrostatic potential ( Vmin) which is found at the carbonyl oxygen center in the S 1' state of the PT tautomer is much deeper than that Vmin located at the hydroxy oxygen center in the S 1 state of the normal tautomer. This observation is interpreted as a significant increase in basicity of the carbonyl oxygen center, this being approximately twice more basic than the hydroxy oxygen center for the first singlet excited electronic state. Therefore, the oxygen center is the most subjected to be perturbed by solvent acidity. The steps followed in this paper for analyzing the response of HBQ to solvent effects can be applied to any molecular system to be used for probing polarity of the environment (e.g., in biopolymers).
Proceedings of The National Academy of Sciences, 1999
The experimental and theoretical bases for a synchronous or concerted double-proton transfer in c... more The experimental and theoretical bases for a synchronous or concerted double-proton transfer in centrosymmetric H-bonded electronically excited molecular dimers are presented. The prototype model is the 7-azaindole dimer. New research offers confirmation of a concerted mechanism for excited-state biprotonic transfer. Recent femtosecond photoionization and coulombic explosion techniques have given rise to time-of-f light MS observations suggesting sequential two-step biprotonic transfer for the same dimer. We interpret the overall species observed in the time-of-f light experiments as explicable without conf lict with the concerted mechanism of proton transfer.
International Journal of Quantum Chemistry, 1999
Skip to Main Content. ...
International Journal of Quantum Chemistry, 2000
Skip to Main Content. ...
Journal of Physical Chemistry A, 1997
... David Gormin, Alexander Sytnik, and Michael Kasha*. Institute of Molecular Biophysics and Dep... more ... David Gormin, Alexander Sytnik, and Michael Kasha*. Institute of Molecular Biophysics and Department of Chemistry, Florida State University, Tallahassee, Florida 32306-3015. J. Phys. Chem. A , 1997, 101 (4), pp 672677. DOI ...
Journal of Luminescence, 1997
Photophysical characterization of perimidine 1, 1-methylperimidine 2, 2-phenylperimidine 3, 1-met... more Photophysical characterization of perimidine 1, 1-methylperimidine 2, 2-phenylperimidine 3, 1-methyl-2-phenylperimidine 4, 2-(2'-hydroxyphenyl)perimidine 5, 1-methyl-2-(2'-hydroxyphenyl)perimidine 6, 2-@'-methoxyphenyl)perimidine 7 and 1-methyl-2-(2'-methoxyphenyl)perimidine 8 has been achieved. All derivatives exhibit a high photostability against the UV light with small photochemical quantum yields 4, in the range of 1O-5-1O-6, implying that non-radiative processes different from the excited state intramolecular proton transfer (ESIPT) mechanism are responsible for their photophysics.
Journal of Organic Chemistry, 1995
Two new families of compounds, the 3(5)-(1'-hydroxy-2'-naphthyl)pyrazoles (a series) and the 3(5)... more Two new families of compounds, the 3(5)-(1'-hydroxy-2'-naphthyl)pyrazoles (a series) and the 3(5)-(2'-hydroxy-l'-naphthyl)pyrazoles (b series), have been synthesized and fully characterized. The use of NMR (lH and I3C) and W (absorption and emission) spectroscopies in different solvents led us to determine the major tautomers, the coplanarity of both rings (naphthyl and pyrazolyl) if present, and the existence of hydrogen bonds. The photostability of a representative set of such derivatives was also determined, showing that the existence of a n intramolecular hydrogen bond (IMHB) is not a n essential condition for providing W stability. Moreover when such an IMHB is present in the molecule, the photostability is not dependent on whether the proton is transferred or not. Abstract published in Advance ACS Abstracts, May 1, 1995. (1) For part 3, see: Catalln, J.; del Valle, J. C.; Claramunt, R. M.; Sanz, D.; Dotor, J. Chem. Phys. Lett. Submitted. (2) Catalln, J.; Fabero, F.; Claramunt, R. M.; Santa Maria, M. D.; Foces-Foces, M. C.; Hernlndez-Cano, F.; Martinez-Ripoll, M.; Elguero, J.; Sastre, R. J . Am. Chem. SOC. 1992, 114, 5039.
Proceedings of The National Academy of Sciences, 2002
A mechanism is proposed for the formation in gas phase, during a short time, of the delicately sy... more A mechanism is proposed for the formation in gas phase, during a short time, of the delicately symmetrical coplanar C2h classic 7-azaindole (7AI) doubly hydrogen-bonded dimer. Of the five card-pack or otherwise random geometry structures most likely to be formed in the supersonic jet expansion molecular beam, none would be an obvious precursor to the C2h dimer. One unstable dimer with dipole-dipole, van der Waals, and plane-to-plane hydrogen bonding is shown to be capable of unhinging about the hydrogen-bond pair as an axis, from 0° to 90° to 180°, yielding a deep minimum for the C2h structure with its delicate geometry and symmetry. This relaxation mechanism is feasible in the 3-μs interval between the nozzle escape and the first laser pulse interception of the molecular beam. In the second part of the paper four published mechanisms are compared for concerted vs. two-step biprotonic phototransfer for the 7AI dimers. The dependence of the latter two models on H-atom instead of proton-transfer as an intermediate step negates the mechanism in a singlet (,*) electronic state by the valency repulsion, in the 3-electron orbital that would be generated. The concerted mechanism for biprotonic phototransfer is reaffirmed by the analysis of the quantum mechanical conditions set on the biprotonic transfer in the photo-excited molecular 7AI pair.
Journal of Physical Chemistry A, 2008
Methylation at the 1N position of 2-phenylimidazole provides the shortest wavelength for a liquid... more Methylation at the 1N position of 2-phenylimidazole provides the shortest wavelength for a liquid-state laser dye reported to date; that is, the 1-methyl-2-phenylimidazole molecule in cyclohexane solution yields amplified spontaneous emission (ASE) with a peak wavelength at 314.5 nm and a constant laser gain value of 5 cm -1 from 310 to 317 nm. Methyl substitution in this case favors the appearance of laser action (owing to a torsion-vibrational mechanism) in cyclohexane as compared with the nonmethylated species which does not exhibit ASE in this solvent. The 2-(2′-hydroxyphenyl)imidazole molecules give rise to ASE with high gain values (ca. 9 cm -1 ) at 450 and 466 nm. The mechanism of population inversion is understood in terms of a vibronic coupling between the hydroxyl stretching motion and the torsional vibration of the phenyl and imidazole rings. The proton-transfer spectroscopy of 2-(2′-hydroxyphenyl)imidazoles is studied in dioxane, cyclohexane, dimethyl sulfoxide, methanol, and water. The greater the acidity of the solvent the greater the disruption of the intramolecular hydrogen bond; solvent acidity is the main parameter which favors formation of the open-form species in the ground electronic state. Methyl substitution at the 1N position favors formation of the open species for 2-hydroxyphenylimidazoles in the ground electronic state, which decreases their own capacity to undergo ASE. Low-temperature absorption spectroscopy confirms aggregation processes for 2-(2′hydroxyphenyl)imidazoles in solution. In accordance with X-ray analyses in the solid phase, these molecules form associations through intermolecular chains of the type NsH · · · O or OsH · · · N.
Journal of The American Chemical Society, 1993
Two new families of compounds, the 3(5)-(1'-hydroxy-2'-naphthyl)pyrazoles (a series) and the 3(5)... more Two new families of compounds, the 3(5)-(1'-hydroxy-2'-naphthyl)pyrazoles (a series) and the 3(5)-(2'-hydroxy-l'-naphthyl)pyrazoles (b series), have been synthesized and fully characterized. The use of NMR (lH and I3C) and W (absorption and emission) spectroscopies in different solvents led us to determine the major tautomers, the coplanarity of both rings (naphthyl and pyrazolyl) if present, and the existence of hydrogen bonds. The photostability of a representative set of such derivatives was also determined, showing that the existence of a n intramolecular hydrogen bond (IMHB) is not a n essential condition for providing W stability. Moreover when such an IMHB is present in the molecule, the photostability is not dependent on whether the proton is transferred or not. Abstract published in Advance ACS Abstracts, May 1, 1995. (1) For part 3, see: Catalln, J.; del Valle, J. C.; Claramunt, R. M.; Sanz, D.; Dotor, J. Chem. Phys. Lett. Submitted. (2) Catalln, J.; Fabero, F.; Claramunt, R. M.; Santa Maria, M. D.; Foces-Foces, M. C.; Hernlndez-Cano, F.; Martinez-Ripoll, M.; Elguero, J.; Sastre, R. J . Am. Chem. SOC. 1992, 114, 5039.
Chemical Physics Letters, 2000
w In this Letter we consider the second laser-pulse time delay experiments of Castleman and co-wo... more w In this Letter we consider the second laser-pulse time delay experiments of Castleman and co-workers D.E. Folmer, L.
Journal of The Chemical Society-perkin Transactions 2, 1995
Journal of Physical Chemistry A, 1999
Chemical Physics Letters, 1996
A spectroscopic study of the fluorescence, amplified spontaneous emission (ASE), and gain spectra... more A spectroscopic study of the fluorescence, amplified spontaneous emission (ASE), and gain spectra is made, testing for UV lasing from several phenyloxazoles. ASE laser spikes occur at 333 and 349 nm for 2-phenylbenzoxazole (PBO), 356 and 374 nm for 2,5-diphenyloxazole (PPO) and 365 and 385 nm for 2-(1-naphthyl)-5-phenyl-l,3,4-oxadiazole (ct-NPD), all in hydrocarbon solution at 298 K. For DPOPOP, 1,4-bis(4-methyl-5-phenyloxazol-2-yl)benzene, the ASE laser spike occurs at 420 nm. The gain coefficients range from 5 to 10 cm-1. Unorthodox features in the ASE spectroscopy serve as a clue to the electronic excitation dynamics of complex composite molecular systems.