Revealing the Photophysical and Photochemical Reaction Processes of Carprofen in Different Solutions via Ultrafast Femtosecond to Nanosecond Transient Absorption

Ultrafast transient absorption spectroscopy and density functional theory calculations are utilized to get a better understanding of photophysical and photochemical reaction mechanisms of AB-Me, AB-Pr, AB-Br and AB-Cl.

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Ultrafast transient absorption investigation on the photochemical reaction mechanisms of selected aromatic carbonyl compounds

10.32655/asc_8-10_dec2020.8 ◽

2020 ◽

Author(s):

Ma Jianni ◽

Guo Yan ◽

Phillips David Lee

Keyword(s):

Reaction Mechanisms ◽

Carbonyl Compounds ◽

Photochemical Reaction ◽

Transient Absorption ◽

Ultrafast Transient Absorption ◽

Aromatic Carbonyl Compounds

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Femtosecond to microsecond observation of the photochemical reaction of 1,2-di(quinolin-2-yl)disulfide with methyl methacrylate

Physical Chemistry Chemical Physics ◽

10.1039/c7cp01784g ◽

2017 ◽

Vol 19 (20) ◽

pp. 12981-12991 ◽

Cited By ~ 12

Author(s):

Daisuke Koyama ◽

Paul M. Donaldson ◽

Andrew J. Orr-Ewing

Keyword(s):

Methyl Methacrylate ◽

Absorption Spectroscopy ◽

Photochemical Reaction ◽

Transient Absorption ◽

Radical Reaction ◽

Transient Absorption Spectroscopy ◽

Continuous Sequence

Multiple radical reaction steps have been observed in a continuous sequence with sub-picosecond to microsecond transient absorption spectroscopy.

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Lifetime Prediction of Tires with Regard to Oxidative Aging5

Tire Science and Technology ◽

10.2346/1.2839371 ◽

2008 ◽

Vol 36 (1) ◽

pp. 63-79 ◽

Cited By ~ 4

Author(s):

L. Nasdala ◽

Y. Wei ◽

H. Rothert ◽

M. Kaliske

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Temperature Distribution ◽

Superposition Principle ◽

Accelerated Aging ◽

Material Model ◽

Aging Behavior ◽

Element Analysis ◽

Material Parameters ◽

Reaction Processes

Abstract It is a challenging task in the design of automobile tires to predict lifetime and performance on the basis of numerical simulations. Several factors have to be taken into account to correctly estimate the aging behavior. This paper focuses on oxygen reaction processes which, apart from mechanical and thermal aspects, effect the tire durability. The material parameters needed to describe the temperature-dependent oxygen diffusion and reaction processes are derived by means of the time–temperature–superposition principle from modulus profiling tests. These experiments are designed to examine the diffusion-limited oxidation (DLO) effect which occurs when accelerated aging tests are performed. For the cord-reinforced rubber composites, homogenization techniques are adopted to obtain effective material parameters (diffusivities and reaction constants). The selection and arrangement of rubber components influence the temperature distribution and the oxygen penetration depth which impact tire durability. The goal of this paper is to establish a finite element analysis based criterion to predict lifetime with respect to oxidative aging. The finite element analysis is carried out in three stages. First the heat generation rate distribution is calculated using a viscoelastic material model. Then the temperature distribution can be determined. In the third step we evaluate the oxygen distribution or rather the oxygen consumption rate, which is a measure for the tire lifetime. Thus, the aging behavior of different kinds of tires can be compared. Numerical examples show how diffusivities, reaction coefficients, and temperature influence the durability of different tire parts. It is found that due to the DLO effect, some interior parts may age slower even if the temperature is increased.

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Thymine Dimerization Induced by Oxidative DNA Lesions and Epigenetic Intermediates via Triplet-Triplet Energy Transfer

10.26434/chemrxiv.12782270 ◽

2020 ◽

Author(s):

Mauricio Lineros-Rosa ◽

Antonio Francés-Monerris ◽

Antonio Monari ◽

Miguel Angél Miranda ◽

Virginie Lhiaubet-Vallet

Keyword(s):

Energy Transfer ◽

Excitation Energy ◽

Transient Absorption ◽

Theoretical Calculations ◽

Dna Lesions ◽

Transient Absorption Spectroscopy ◽

Triplet Energy ◽

Pyrimidine Dimers ◽

Triplet Energy Transfer ◽

Dna Nucleobases

Interaction of nucleic acids with light is a scientific question of paramount relevance not only in the understanding of life functioning and evolution, but also in the insurgence of diseases such as malignant skin cancer and in the development of biomarkers and novel light-assisted therapeutic tools. This work shows that the UVA portion of sunlight, not absorbed by canonical DNA nucleobases, can be absorbed by 5-formyluracil (ForU) and 5-formylcytosine (ForC), two ubiquitous oxidative lesions and epigenetic intermediates present in living beings in natural conditions. We measure the strong propensity of these molecules to populate triplet excited states able to transfer the excitation energy to thymine-thymine dyads, inducing the formation of the highly toxic and mutagenic cyclobutane pyrimidine dimers (CPDs). By using steady-state and transient absorption spectroscopy, NMR, HPLC, and theoretical calculations, we quantify the differences in the triplet-triplet energy transfer mediated by ForU and ForC, revealing that the former is much more efficient in delivering the excitation energy and producing the CPD photoproduct. Although significantly slower than ForU, ForC is also able to harm DNA nucleobases and therefore this process has to be taken into account as a viable photosensitization mechanism. The present findings evidence a rich photochemistry crucial to understand DNA photodamage and of potential use in the development of biomarkers and non-conventional photodynamic therapy agents.

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Catalyst Halogenation Enables Rapid and Efficient Polymerizations with Visible to Near-Infrared Light

10.26434/chemrxiv.12588965 ◽

2020 ◽

Author(s):

Alex Stafford ◽

Dowon Ahn ◽

Emily Raulerson ◽

Kun-You Chung ◽

Kaihong Sun ◽

...

Keyword(s):

Near Infrared ◽

Transient Absorption ◽

Reaction Times ◽

Infrared Light ◽

Structure Property ◽

Light Emitting ◽

Structure Property Relationships ◽

Nir Light ◽

Light Intensities ◽

Emission Quenching

Driving rapid polymerizations with visible to near-infrared (NIR) light will enable nascent technologies in the emerging fields of bio- and composite-printing. However, current photopolymerization strategies are limited by long reaction times, high light intensities, and/or large catalyst loadings. Improving efficiency remains elusive without a comprehensive, mechanistic evaluation of photocatalysis to better understand how composition relates to polymerization metrics. With this objective in mind, a series of methine- and aza-bridged boron dipyrromethene (BODIPY) derivatives were synthesized and systematically characterized to elucidate key structure-property relationships that facilitate efficient photopolymerization driven by visible to NIR light. For both BODIPY scaffolds, halogenation was shown as a general method to increase polymerization rate, quantitatively characterized using a custom real-time infrared spectroscopy setup. Furthermore, a combination of steady-state emission quenching experiments, electronic structure calculations, and ultrafast transient absorption revealed that efficient intersystem crossing to the lowest excited triplet state upon halogenation was a key mechanistic step to achieving rapid photopolymerization reactions. Unprecedented polymerization rates were achieved with extremely low light intensities (< 1 mW/cm<sup>2</sup>) and catalyst loadings (< 50 μM), exemplified by reaction completion within 60 seconds of irradiation using green, red, and NIR light-emitting diodes.

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