Photoelimination of Nitrogen from Diazoalkanes: Involvement of Higher Excited Singlet States in the Carbene Formation

Piteša, Tomislav; Alešković, Marija; Becker, Kristin; Basarić, Nikola; Došlić, Nađa

doi:10.1021/jacs.0c02221

Cited by 6 publications

(31 citation statements)

References 46 publications

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“…The minimum conformers of 1 and singlet and triplet car-1 exhibit the C 2 point group symmetry; similar structures were reported previously. 22,40 The conformational preferences in 1, 2, and 3 reflect the compromise between the reduction of the steric strain with respect to the two bulky substituents and the enhancement of the conjugation between the C−N−N and benzene π-densities. The two opposing effects determine the optimal angles closed by the C−N−N axis and the plane of the benzene ring, which equal 29°, 7°, and 19°in 1, 2, and 3, 46 This is also the case here and leads to the larger first IP and the more hindered rotation in 3 compared to 2 (vide supra).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Prompted by the observation of fluorescence for 2 and 3, we investigated if these molecules show anti-Kasha photochemistry. Preparative irradiations for 2 22 and 3 were performed in cyclohexane and benzene upon excitation with visible light (cool white lamps, corresponding to the population of S 1 ) or at ≈300 nm, giving rise to a population of S n (where n > 1).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…This observation is in line with the deactivation of the S 2 state in 1 and 2 via locally nonplanar conformations of the CI, as was observed in the nonadiabatic MD runs. 22 In the S 1 state, the charge is transferred mainly locally within the C−N−N π-system. While this also weakens the C−N bond, the effect is less pronounced than that in S 2 .…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Ultrafast Photoelimination of Nitrogen from Upper Excited States of Diazoalkanes and the Fate of Carbenes Formed in the Reaction

et al. 2023

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The photochemical reactivity of diphenyldiazomethane 1 and phenyl 1- and 2-adamantyl diazomethanes 2 and 3, respectively, was investigated by transient absorption spectroscopy (TA). Photoelimination of N2 upon UV excitation takes place in the anti-Kasha ultrafast photochemical reaction from the upper excited singlet states to deliver singlet carbenes, which were, in the case of 1 and 2, detected by fs-TA. The reactivity of the carbenes differs with respect to the substituent at the carbene center. The singlet car-1 in a nonpolar solvent delivers the triplet carbene by intersystem crossing (ISC). Singlet car-2 does not undergo ISC but reacts in the intermolecular insertion reactions into C–H bonds. Car-3 has an α-C–H bond next to the carbene center and reacts rapidly in the intramolecular C–H insertion reaction to deliver alkene, precluding its detection by fs-TA. However, the isolation of ketone photoproducts from 3 is highly indicative of triplet car-3’s intermediate formation. The TA spectra from the S1–S3 states of 1–3 were computed using time-dependent density functional theory, while the multiconfigurational perturbation theory to the second order was used for the absorption spectra of the corresponding singlet and triplet carbenes. The modeled and measured spectra are in good agreement, and the computations corroborate the assignments of the key short-lived intermediates.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

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Ultrafast Photoelimination of Nitrogen from Upper Excited States of Diazoalkanes and the Fate of Carbenes Formed in the Reaction

et al. 2023

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“…Carbenes can be produced upon photolysis of ketones, diazo compounds, or diazirines. − Curiously, while diazo compounds have been used in synthetic chemistry, their structural isomers (diazirines) have been reserved to other applications as photolabeling reagents of proteins , or polymer cross-linking . The trend with diazirines has changed only recently. , …”

Section: Introductionmentioning

confidence: 99%

Photochemistry of 1-Phenyl-1-diazopropane and Its Diazirine Isomer: A CASSCF and MS-CASPT2 Study

Soto

2022

J. Phys. Chem. A

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In this work, we studied the wavelength (520 or 350 nm) dependence of the photochemical decomposition of 1-phenyl-1-diazopropane (PDP) and 1-phenyl-1-propyl diazirine (PED) by means of high-level ab initio quantum chemical calculations (CASSCF and MS-CASPT2) to obtain qualitative and quantitative results. It is found that the photochemistry of PDP is governed by nonradiative deactivation processes that can involve one or two S1/S0 conical intersections (CI1 and CI2) depending on the wavelength of the radiation; CI2 is only accessible at the shortest wavelength. It is demonstrated that the main intermediate of the photochemistry of the titled compounds is 1-ethyl-1-phenyl carbene (EPC). Upon irradiation of PDP with the 520 nm light, the carbene is always generated in its ground state as closed-shell singlet carbene. In contrast, the 350 nm radiation can directly decompose PDP into S1 carbene (open shell) and N2 when the conical intersection CI2 is avoided. Once the carbene is formed in the S1 state, it can experience excited state intramolecular proton transfer along a seam of crossing (ESIPT-SC) of the S1 and S0 states to yield the alkene derivative; that is, the proton transfer reaction takes places on a degenerate potential energy surface where the two electronic states have equal energy. In addition, it is found that EPC absorbs at 350 nm (double excitations); therefore, there is another possible route that can induce as well a slightly different photochemistry in changing the wavelength of the radiation because the shortest wavelength (when it is intense enough) decreases the amount of available EPC or generates a highly vibrationally excited state of the carbene; that is, after 350 nm excitation, the carbene intermediate can deactivate via radiation emission or can decay through a cascade of conical intersections to its first excited state (S1), where ESIPT-SC is operative again.

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“…Questions regarding the exact proton transfer time and relaxation pathways from the excited states are still to be resolved. In this scenario, computational studies are of great help and, in particular, static and dynamical studies with wave function-based methods such as second-order coupled-cluster (CC2), the second-order algebraic diagrammatic construction (ADC(2)), , or, if possible, multiconfigurational methods such as CASSCF , methods, add to our understanding, which has been highlighted in many recent studies. − To the best of our knowledge, the static and dynamic studies reported earlier were confined only to the proton transfer process and the various relaxation pathways have not been explored. The present study is carried out with the objective of illustrating various excited-state processes, including proton transfer and two different pathways of deactivation in HAN at ADC(2) and complete active space second-order perturbation theory (CASPT2) levels of theories.…”

Section: Introductionmentioning

confidence: 99%

Insights into the Excited-State Processes in 1-Hydroxy-2-acetonaphthone at ADC(2) and CASSCF Levels

Mawa

Panda

2021

J. Phys. Chem. A

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1-Hydroxy-2-acetonaphthone (HAN) has been extensively studied both experimentally and computationally to ascertain the existence of the excited-state proton transfer process. However, the process of full photocycle including the nonradiative relaxation pathways is yet to be proposed. Therefore, in the present study, we aim at providing a comprehensive picture of the excited-state processes in HAN including the proton transfer and relaxation processes through electronic structure calculations at second-order algebraic diagrammatic construction (ADC(2)) and complete active space second-order perturbation theory (CASPT2)//complete active space self-consistent field (CASSCF) and dynamics simulations at ADC(2) levels. Our studies show that the proton transfer process in the S1 state is barrierless and produces a stable keto form, which is in accordance with previous experimental and computational studies. Adiabatic dynamics simulations at the ADC(2) level confirmed the ultrafast process with an average proton transfer time of 43 fs. The resultant keto conformer then undergoes torsional rotation, leading to a conical intersection that mediates the internal conversion process to the ground state. Our dynamics simulation predicted that this deactivation process occurs at a time scale beyond 600 fs of simulation time. We also explored nonradiative relaxation from the enol Franck–Condon region, and this process was found to be improbable from the static point of view at both the ADC(2) and CASPT2 levels of theory due to a high energy barrier along the torsional coordinate.

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Photoelimination of Nitrogen from Diazoalkanes: Involvement of Higher Excited Singlet States in the Carbene Formation

Cited by 6 publications

References 46 publications

Ultrafast Photoelimination of Nitrogen from Upper Excited States of Diazoalkanes and the Fate of Carbenes Formed in the Reaction

Ultrafast Photoelimination of Nitrogen from Upper Excited States of Diazoalkanes and the Fate of Carbenes Formed in the Reaction

Photochemistry of 1-Phenyl-1-diazopropane and Its Diazirine Isomer: A CASSCF and MS-CASPT2 Study

Insights into the Excited-State Processes in 1-Hydroxy-2-acetonaphthone at ADC(2) and CASSCF Levels

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