Photoisomerism: A Colorless Photoinduced Intermediate of
            <i>o</i>
            -Nitrobenzylpyridine

Sousa, John A.; Loconti, J. D.

doi:10.1126/science.146.3642.397

Cited by 6 publications

(7 citation statements)

References 8 publications

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“…Preliminary Observations. It has been known for over 30 years that no detectable coloration appears after UV irradiation of polymer samples doped with α-DNBP at liquid nitrogen temperature but that heating a previously irradiated sample in the dark results in a transient blue coloration . This behavior reflects the existence of a colorless precursor in the photochromism of α-DNBP, in agreement with the results of ref described in the Introduction.…”

Section: Resultssupporting

confidence: 88%

“…It has been known for over 30 years that no detectable coloration appears after UV irradiation of polymer samples doped with R-DNBP at liquid nitrogen temperature but that heating a previously irradiated sample in the dark results in a transient blue coloration. 8 This behavior reflects the existence of a colorless precursor in the photochromism of R-DNBP, in agreement with the results of ref 6 described in the Introduction. Thus, a more systematic study of this "trapping" phenomenon has been carried out at low temperature to study the colorless reaction intermediate assigned to be the P form (Figure 1), by monitoring the effect of irradiation duration and temperature variations on solid samples.…”

Section: Preliminary Observationssupporting

confidence: 91%

“…8 This behavior reflects the existence of a colorless precursor in the photochromism of R-DNBP, in agreement with the results of ref 6 described in the Introduction. Thus, a more systematic study of this "trapping" phenomenon has been carried out at low temperature to study the colorless reaction intermediate assigned to be the P form (Figure 1), by monitoring the effect of irradiation duration and temperature variations on solid samples.…”

Section: Preliminary Observationssupporting

confidence: 80%

“…Because the kinetic data available shows that this is unlikely for R-DNBP crystals, we have turned to the study of polymer samples, in which such a process has been already observed. 8 …”

Section: Preliminary Observationsmentioning

confidence: 99%

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New Insights on the Photochromism of 2-(2‘,4‘-Dinitrobenzyl)pyridine

2002

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The photochromic behavior of 2-(2′,4′-dinitrobenzyl)pyridine (R-DNBP) has been followed in poly(methyl methacrylate) (PMMA) films and benzene solutions to clarify the behavior of a precursor state, previously identified in studies on crystalline R-DNBP at low temperatures. In PMMA films, photolysis at temperatures e50 K led to the concurrent formation of a NH tautomer and a colorless intermediate, which was stable for several hours. On irradiation at low temperatures and warming the sample, the colorless intermediate was seen to react to produce the NH tautomer in a higher yield than that found in the direct photolysis. Further information on this intermediate has come from flash photolysis studies in benzene solution, in which a new transient absorption has been observed at 335 nm and assigned to this species. This decays within a few microseconds at room temperature to form an OH tautomer, which then interconverts to the NH tautomer. The precursor state is not quenched by oxygen or naphthalene. From consideration of the kinetic and spectral data, it is suggested that this new species corresponds to a nonrelaxed tautomeric form of the OH state of R-DNBP.

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Section: Resultssupporting

confidence: 88%

Section: Preliminary Observationssupporting

confidence: 91%

Section: Preliminary Observationssupporting

confidence: 80%

“…Because the kinetic data available shows that this is unlikely for R-DNBP crystals, we have turned to the study of polymer samples, in which such a process has been already observed. 8 …”

Section: Preliminary Observationsmentioning

confidence: 99%

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New Insights on the Photochromism of 2-(2‘,4‘-Dinitrobenzyl)pyridine

2002

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“…Theoretical investigations such as semi-empirical (PM3) calculations, ab initio, and density functional theory (DFT) calculations , were also performed. While the slow dynamics (nanoseconds to microseconds to milliseconds and even seconds) is well understood, ,, the ultrafast PIPT dynamics (femtosecond to picosecond timescale) still largely remains unresolved. ,,,,,,,,,− Vibrational spectroscopic techniques including infrared (IR) spectroscopy as well as various linear and nonlinear Raman spectroscopies − offer the advantage that they provide chemical specificity by probing functional groups based on their intrinsic “molecular fingerprint”. IR spectroscopy has been performed on samples of α-DNBP in potassium bromide wafer and sodium chloride pellets in dark and after irradiation.…”

Section: Introductionmentioning

confidence: 99%

Vibrational Spectroscopic Characterization of 2-(2,4-Dinitrobenzyl)-pyridine (α-DNBP) in Solution by Polarization-Resolved Spontaneous Raman Scattering and Broadband CARS

2019

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The photochromic molecule 2-(2,4-dinitro-benzyl)-pyridine (α-DNBP) is characterized in solution by a combination of density functional theory employing a polarizable continuum model and polarization-resolved spontaneous and nonlinear Raman spectroscopies. By the comparison of theoretically predicted wavenumber positions and depolarization ratios with the experimental spectra acquired under electronically nonresonant conditions, polarized and depolarized Raman bands are assigned. Specifically, the symmetric stretching vibrations of the two nitro groups in ortho and para positions to the pyridine ring can be experimentally differentiated, mainly because of their different Raman depolarization ratios, which supports our prediction from theory. Compared to the polarization-resolved spontaneous Raman experiments, the vibrational spectroscopic differentiation of the two nitro groups is more pronounced in time-delayed polarization-resolved coherent anti-Stokes Raman scattering experiments. Overall, this linear and nonlinear vibrational spectroscopic characterization of the CH form paves the way for the interpretation of future time-resolved pump/nonlinear Raman probe studies on the ultrafast photoinduced intramolecular proton transfer in α-DNBP involving a nitro group as an intramolecular proton acceptor.

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Latent photochromism (pseudothermochromism) and photofatigue of crystalline 2‐(2′,4′‐dinitrobenzyl)pyridine

Naumov

Ohashi

2004

J of Physical Organic Chem

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Along with the metastable 2‐(2′,4′‐dinitrophenylmethylidene)‐1,2‐dihydropyridine (NH) and the unstable 6‐aci‐nitro‐2‐nitro‐5‐(2′‐pyridylmethylene)‐1,3‐cyclohexadiene (OH), the stable form of 2‐(2′,4′‐dinitrobenzyl)pyridine (DNBP), CH, is photochemically converted into small amounts of 1,2‐bis(2′,4′‐dinitrophenyl)‐1,2‐bis(2′‐pyridyl)ethane, trans‐bis[5‐nitro‐2‐(pyridine‐2‐carbonyl)phenyl]diazene N‐oxide, 6‐nitro‐3‐(2′‐pyridyl)‐2,1‐benzisoxazole and 3‐nitropyrido[1,2‐b]quinolin‐6‐ium‐11‐olate. The latent photochromism of DNBP, as shown by x‐ray analysis of the structures of the side‐products and ESR/IR measurements, is attributed to open‐shell reactions that are initiated by hydrogen photoabstraction and subsequent creation of two monoradicals, NH. and OH.. Large amounts of the radicals (ca 50% NH. and 70% OH.) confined in the crystalline interior are persistent under ambient conditions. Through quasi‐periodic reactions, the remaining radicals partially recover the ground‐state isomers CH, NH and OH, or decay to the side‐products, which results in crystalline photofatigue. Together with proton tunneling from the excited CH, the radical reactions represent dominant mechanism for the creation of NH and OH in the low‐temperature regimes, but are successfully competed by the closed‐shell reactions at higher temperatures. The precursor state, whose existence was assumed previously from transient absorption spectroscopy, may be identified as the radical OH.. The present work represents the first study of the photofatigue of a 2‐(2′,4′‐dinitrobenzyl)pyridine compound and extends the ‘classical’ mechanism of the photochromic reactions of nitrobenzylpyridines with a set of open‐shell radical reaction routes. Copyright © 2004 John Wiley & Sons, Ltd.

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Photoisomerism: A Colorless Photoinduced Intermediate of o -Nitrobenzylpyridine

Abstract: Exposure to light of o-nitrobenzylpyridines at -185 degrees C yields a long-lived colorless intermediate which is converted to a colored isomer on warming.

Cited by 6 publications

References 8 publications

New Insights on the Photochromism of 2-(2‘,4‘-Dinitrobenzyl)pyridine

New Insights on the Photochromism of 2-(2‘,4‘-Dinitrobenzyl)pyridine

Vibrational Spectroscopic Characterization of 2-(2,4-Dinitrobenzyl)-pyridine (α-DNBP) in Solution by Polarization-Resolved Spontaneous Raman Scattering and Broadband CARS

Latent photochromism (pseudothermochromism) and photofatigue of crystalline 2‐(2′,4′‐dinitrobenzyl)pyridine

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