A Unified View of Ketone Photochemistry

Formosinho, Sebastião J.; Arnaut, Luı́s G.

doi:10.1002/9780470133460.ch2

Cited by 49 publications

(9 citation statements)

References 204 publications

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“…1b. Taking into account the distributive properties of the integral and the partial derivative of w 1 , and considering only the first member of the T(t) equation (eqn ( 14)), the convolution expression for a monoexponential heat decay is: (16) and the complete solution is: (17) where S 11 , S 12 , S 13 and S 14 are given by eqn ( 18)-( 21). This result can be extended for a multiexponential case, simply by using the kinetic expression H(t) for consecutive decays.…”

Section: E(t) = T(t) ƒ H(t) (15)mentioning

confidence: 99%

Analytical solution for time-resolved photoacoustic calorimetry data and applications to two typical photoreactions

Schaberle

Nunes

Barroso

et al. 2010

Photochem Photobiol Sci

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Time-resolved photoacoustic calorimetry (PAC) allows the measurement of lifetimes and energy fractions of molecular nonradiative deactivation processes, as well as structural volume changes associated with such processes. The photoinduced acoustic wave generated by a given photochemical sample, E(t), is the result of the convolution between the heat function H(t), describing the kinetics of the photochemical processes in the sample, and the instrument response given by a calorimetric reference wave, T(t). A relatively simple mathematical description of the T(t) wave parametrized by the rise time, frequencies and damping time of the transducer is presented for transducers of distinct frequencies. This description allows for a non-restrictive analytical solution of the convolution of the T(t) wave with the heat function. Comparison of the analytical solution with the experimental wave E(t) allows the determination of the fractions of excitation energy and lifetimes of the intermediate species. Published photochemical systems with two and three sequential decaying processes were analyzed to validate the efficacy of this method. This new method of analysis, and a software application that simulates E(t), allows a better understanding of the underlying physics through their phenomenological description.

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Section: E(t) = T(t) ƒ H(t) (15)mentioning

confidence: 99%

Analytical solution for time-resolved photoacoustic calorimetry data and applications to two typical photoreactions

Schaberle

Nunes

Barroso

et al. 2010

Photochem Photobiol Sci

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“…The tunnelling rate can now be expressed as the product between the frequency of impact in the barrier and its permeability [1,33,34] k tun Z c6kðWÞ (21) This expression can be employed directly when DV 0 ad % 0, on the assumption that the system can be described by particle of mass m and energy WZk B T. For endothermic reactions, the particle can only tunnel if it has at least an energy of DV 0 ad . Thus, the tunnelling rate of endothermic reactions must be multiplied by expðKDV 0 ad =k B TÞ.…”

Section: K1mentioning

confidence: 99%

Tunnelling in low-temperature hydrogen-atom and proton transfers

Arnaut

Formosinho

Barroso

2006

Journal of Molecular Structure

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The reaction path of the interacting-state model with the Lippincott-Schroeder potential for hydrogen bonds, is used in transition-state theory calculations with the semiclassical correction for tunnelling (LS-ISM/scTST) to estimate proton and hydrogen-atom transfer rates at low temperatures. Down to 100 K, the semiclassical correction leads to semi-empirical rates and isotope effects that are in good agreement with the thermal tautomerism of porphine, and the excited-state tautomerisms of salicylideneanilines and 2-(2 0 -hydroxyphenyl)benzoxazole. For lower temperatures, the tunnelling corrections become extremely high and unreliable. It is shown that the permeability of an Eckart barrier fitted to the curvature of the LS-ISM reaction path leads to good estimates of these reaction rates down to 2 K. q

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“…Dauben–Salem–Turro′s rules classify photochemical reactions, assuming they are controlled by the generation of primary products with diradicaloid character. Under continuous near‐UV light illumination, aldehydes and ketones react in organic solvents by radical reactions, for example, hydrogen abstraction . We ask if this is also the case in protic solvents like water.…”

Section: Figurementioning

confidence: 91%

“…The photochemistry of ketones and aldehydes is well studied and exploited in organic synthesis . Dauben–Salem–Turro′s rules classify photochemical reactions, assuming they are controlled by the generation of primary products with diradicaloid character.…”

Section: Figurementioning

confidence: 99%

Fluorescence Quenching of Benzaldehyde in Water by Hydrogen Atom Abstraction

2016

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We computed the mechanism of fluorescence quenching of benzaldehyde in water through relaxed potential energy surface scans. Time-dependent density functional theory calculations along the protonation coordinate from water to benzaldehyde reveal that photoexcitation to the bright ππ* (S3 ) state is immediately followed by ultrafast decay to the nπ* (S1 ) state. Evolving along this state, benzaldehyde (BA) abstracts a hydrogen atom, resulting in a BAH(.) and OH(.) radical pair. Benzaldehyde does not act as photobase in water, but abstracts a hydrogen atom from a nearby solvent molecule. The system finally decays back to the ground state by non-radiative decay and an electron transfers back to the OH(.) radical. Proton transfer from BAH(+) to OH(-) restores the initial situation, BA in water.

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A Unified View of Ketone Photochemistry

Cited by 49 publications

References 204 publications

Analytical solution for time-resolved photoacoustic calorimetry data and applications to two typical photoreactions

Analytical solution for time-resolved photoacoustic calorimetry data and applications to two typical photoreactions

Tunnelling in low-temperature hydrogen-atom and proton transfers

Fluorescence Quenching of Benzaldehyde in Water by Hydrogen Atom Abstraction

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