- Photophysics and kinetics of naphthopyran derivatives, Part 2: Analysis of diarylnaphthopyran kinetics. Degeneracy of the kinetic solution
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The photocoloring and fading kinetics of the photochromic 3,3-diphenyl-3H-naphtho|2,1-b|pyran (NPY) have been analyzed using a kinetic treatment for three related species recently developed by us (Int J Chem Kinet 2005, 37(3), 162). The concepts of identifiability and distinguishability are developed with respect to the elucidation of the NPY kinetics. We find that neither set of kinetic data on its own, nor the two data sets combined, allow the true mechanism to be distinguished. In addition, even for a chosen mechanism, there exist degenerate sets of parameters i.e. the solutions are also unidentifiable. A discussion of the limits and uniqueness of the results' interpretation is presented.
- Maafi,Brown
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- Ultrafast Dynamics of the Transoid-cis Isomer Formed in Photochromic Reaction from 3H-Naphthopyran
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Recent efforts in designing new 3H-naphthopyran derivatives have been focused on efficient coloration process with a short fading time of the colored transoid-cis TC isomer. It is desirable to avoid photoisomerization of TC leading to transoid-trans TT isomers in the photoreaction. Long lifetime of TT can hamper fast applications such as dynamic holographic materials and molecular actuators, the residual color is one of the serious issues for photochromic lenses. Herein we characterize the photophysical and photochemical channels of TC excited state deactivation competing with the unwanted TC→TT isomerization process. Transient absorption spectroscopy reveals a very short lifetime of the singlet excited TC (≈0.8 ps) and its deactivation channels as S1→S0 internal conversion (major), intersystem crossing S1→T1, pyran ring formation, photoenolization and TC→TT isomerization. Computations support the S1→S0 and T1→S0 channels as responsible for photostabilization of the TC form.
- Brazevic, Sabina,Baranowski, Miko?aj,Sikorski, Marek,Rode, Micha? F.,Burdziński, Gotard
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p. 1402 - 1407
(2020/06/17)
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- A Simple and Versatile Strategy for Rapid Color Fading and Intense Coloration of Photochromic Naphthopyran Families
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Benzo-annulated chromenes, i.e., naphthopyrans, are well-known photochromic molecules that undergo photochemical ring-opening reactions to form two colored open-ring isomers, the transoid-cis and transoid-trans forms, upon light irradiation. Though the transoid-cis form returns thermally to the uncolored closed form, the fading rate of the transoid-trans form is extremely slow because of its higher thermal stability. This slow fading behavior of the transoid-trans form is responsible for the persistence of residual color for several minutes to hours, and prevents the application of such molecules to fast photoswitching materials. We have found a new simple and versatile strategy to substantially reduce the amount of the undesirable long-lived colored transoid-trans form by introducing an alkoxy group at the 1-position of azino-fused chromenes, i.e., 8H-pyranoquinazolines. The alkoxy group effectively reduces the formation of the transoid-trans form due to C-H···O intramolecular hydrogen bonding in the transoid-cis form. Moreover, the introduction of a condensed aromatic ring at the 3-position was found to be effective to increase the photosensitivity of the ring-opening reaction. This strategy can also be applied for naphthopyran derivatives and is useful for the development of fast photoresponsive photochromic lenses and fast photoswitching applications such as dynamic holographic materials and molecular actuators.
- Inagaki, Yuki,Kobayashi, Yoichi,Mutoh, Katsuya,Abe, Jiro
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p. 13429 - 13441
(2017/10/05)
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- Solid-state photochromism of chromenes: Enhanced photocoloration and observation of unstable colored species at low temperatures
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Solid-state photochromism of benzopyrans and naphthopyrans (chromenes) was investigated in the temperature range between 300 and 80 K. Variable-temperature diffuse reflectance spectroscopy of microcrystalline powders showed that the extent of photocoloration was greatly enhanced at low temperatures. All the chromenes examined exhibited solid-state photochromism at low temperatures, even when they showed little or no photocoloration at room temperature. The solid-state photochromic properties of the chromenes were quite similar to those reported for analogous photochromic compounds of spiropyrans and spirooxazines, which indicates that these classes of compounds are generally photochromic even in the solid state. Photobleaching reactions of the colored merocyanine forms proceeded at low temperatures through the formation of a colorless intermediate, instead of directly resuming the original closed form. In addition to two stable planar merocyanine forms, which are usually observed in the photochromic reactions in solution, photoreactions at low temperatures allowed us to observe unstable colored species, which were tentatively assigned as nonplanar cisoid forms, and were stabilized in the solid state at low temperatures.
- Harada, Jun,Ueki, Keigo,Anada, Masahide,Kawazoe, Yuta,Ogawa, Keiichiro
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p. 14111 - 14119
(2012/01/19)
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- A strategy for the design of photochromic naphthopyrans with large optical density at photosteady state and fast fading speed at ambient temperature in the dark
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A photochromic naphthopyran system in which both optical density and fading speed of colored forms are significantly increased has been described. 3-Aryl-3-(α-naphthalene)-3H-naphtho[2,1-b]pyrans showed thermal stability, and a large optical density of colored forms was obtained at ambient temperature. By attachment of an alkoxyl group to the α-naphthalene group, the fading speed of colored forms was dramatically increased, and the fading speed was increased with increase of the length of alkoxyl chain. The generic nature of the system is beneficial for both the design of naphthopyran molecules with large optical density and fast fading speed at ambient temperature and applications.
- Guo, Kunpeng,Chen, Yi
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scheme or table
p. 4193 - 4197
(2011/07/30)
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- Photophysics and kinetics of naphthopyran derivatives, part 3: A general procedure to uniquely identify the kinetic and spectroscopic parameters of ABC(2k,2φ) systems and application to naphthopyran reactions
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A new procedure has been developed with the aim of determining the kinetic and spectroscopic parameters of any photochemical systems of the generic ABC(2k,1φ) and ABC(2k,2φ) types. General expressions of the colorability and the equilibrium concentration ratio of two (of the three involved) species at a photostationary state or a state of thermal equilibrium have been derived. The procedure has been successfully applied to achieve unique identifiability for the seven sequences of the ABC(2k,1φ and 2φ) type that may represent naphthopyran dynamics. It is demonstrated that the reactivity of this particular compound is certainly described by a higher kinetic level than those (three or four reaction steps) considered in the present study.
- Maafi,Brown
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p. 421 - 430
(2008/02/09)
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- Kinetic and structural studies of the photochromic process of 3H-naphthopyrans by UV and NMR spectroscopy
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The photomerocyanines resulting from the UV irradiation of closed colourless 3,3-diphenyl-3H-naphtho[2,1-b]pyran and its 3,3-bis(4-fluorophenyl) derivative have been studied by UV-VIS and NMR spectroscopy. Kinetic bleaching studies have been carried out on a UV-VIS spectrometer at the photostationary state in acetonitrile solution. A thermal biexponential back-isomerization is observed. These two different kinetics can be attributed to two different isomers of the photomerocyanlne. NMR spectroscopy allows us to obtain a 1H, 13C and 19F (where present) structural identification of these two forms: complete assignment for the predominant isomer (trans-cis) and partial assignment for the second one (trans-trans). The presence of a third form (which quickly decays) is also observed. Each open form follows a mono-exponential decay, with very different bleaching rate coefficients. This is the first time that 19F NMR has been used to identify the number and structure of isomers produced by irradiation, illustrating the advantages of this technique.
- Delbaere, Stephanie,Luccioni-Houze, Barbara,Bochu, Christophe,Teral, Yannick,Campredon, Mylene,Vermeerscht, Gaston
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p. 1153 - 1157
(2007/10/03)
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