Photo-induced radical polarization and liquid-state dynamic nuclear polarization using fullerene nitroxide derivatives

Liu, G.; Liou, Shu-Hao; Enkin, Nikolay; Tkach, Igor; Bennati, Marina

doi:10.1039/c7cp06073d

“…The scope for maintaining enhancements using a pulsed laser to produce much lower duty cycle trains of pulses has been discussed elsewhere and remains a target for future experimental investigation. 23 As noted elsewhere the build-up time for the optical enhancement is expected to be governed by the nuclear relaxation time T 1n , 23,37 values for which are given in Table 2. While one might therefore expect maximal polarization to be achieved with illumination for B5T 1n , corresponding to 3.5-7.0 s in the present case, illumination longer than 4 s reduced the enhancement obtained.…”

Section: Nuclear Polarizationmentioning

confidence: 85%

“…This is likely the result of unwanted heating effects when using a high power illumination source, similar to observations of Liu et al who noted polarization build up at twice the expected rate. 37 Laser induced heating was particularly problematic in the most viscous solvent mixture when using the highest illumination power of 2.0 W, with data showing poor reproducibility under these conditions. For this reason only data recorded with illumination powers of up to 1.5 W are presented for samples containing 30% glycerol by volume.…”

Section: Nuclear Polarizationmentioning

confidence: 99%

Viscosity effects on optically generated electron and nuclear spin hyperpolarization

Dale

¹

,

Cheney

²

,

Vallotto

³

et al. 2020

Phys. Chem. Chem. Phys.

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“…To extend the scope of high‐resolution NMR spectroscopic investigations in photocatalysis with stable radicals, a combined NMR and UV/Vis spectroscopic tool would be ideal 10. However, reaction profiles of photocatalytic processes featuring longer reaction times of up to several hours or even days impose severe challenges for separated setups.…”

mentioning

confidence: 99%

Combined In Situ Illumination‐NMR‐UV/Vis Spectroscopy: A New Mechanistic Tool in Photochemistry

Seegerer

¹

,

Nitschke

²

,

Gschwind

³

2018

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Synthetic applications in photochemistry are booming. Despite great progress in the development of new reactions, mechanistic investigations are still challenging. Therefore, we present a fully automated in situ combination of NMR spectroscopy, UV/Vis spectroscopy, and illumination to allow simultaneous and time‐resolved detection of paramagnetic and diamagnetic species. This optical fiber‐based setup enables the first acquisition of combined UV/Vis and NMR spectra in photocatalysis, as demonstrated on a conPET process. Furthermore, the broad applicability of combined UVNMR spectroscopy for light‐induced processes is demonstrated on a structural and quantitative analysis of a photoswitch, including rate modulation and stabilization of transient species by temperature variation. Owing to the flexibility regarding the NMR hardware, temperature, and light sources, we expect wide‐ranging applications of this setup in various research fields.

show abstract

“…To extend the scope of high‐resolution NMR spectroscopic investigations in photocatalysis with stable radicals, a combined NMR and UV/Vis spectroscopic tool would be ideal . However, reaction profiles of photocatalytic processes featuring longer reaction times of up to several hours or even days impose severe challenges for separated setups.…”

Section: Figurementioning

confidence: 99%

Combined In Situ Illumination‐NMR‐UV/Vis Spectroscopy: A New Mechanistic Tool in Photochemistry

Seegerer

¹

,

Nitschke

²

,

Gschwind

³

2018

View full text Add to dashboard Cite

Synthetic applications in photochemistry are booming. Despite great progress in the development of new reactions,m echanistic investigations are still challenging. Therefore,w ep resent af ully automated in situ combination of NMR spectroscopy, UV/Vis spectroscopy, and illumination to allows imultaneous and time-resolved detection of paramagnetic and diamagnetic species.T his optical fiber-based setup enables the first acquisition of combined UV/Vis and NMR spectra in photocatalysis,asdemonstrated on aconPET process.F urthermore,t he broad applicability of combined UVNMR spectroscopyf or light-induced processes is demonstrated on as tructural and quantitative analysis of ap hotoswitch,including rate modulation and stabilization of transient species by temperature variation. Owing to the flexibility regarding the NMR hardware,t emperature,a nd light sources, we expect wide-ranging applications of this setup in various researchfields.Photocatalysis is one of the booming fields in organic synthesis and has experienced an early exponential increase in publications of synthetic strategies and applications during the last decades. [1] Despite the high impact of new lightinduced transformations on synthesis,d etailed insights into photocatalytic mechanisms are still ar eal challenge.I n photochemistry,u ltrafast UV/Vis spectroscopy is so far the most commonly used method for detailed mechanistic studies, owing to its capability to detect the initial photoexcited states. [2] We and other groups have recently shown that NMR spectroscopy can provide essential mechanistic information on photochemical and photocatalytic processes,d espite its insensitivity and poor time resolution, [3] by providing quantitative reaction profiles of reactants,products,and intermediates.C omplementary to ultrafast UV/Vis,m echanistic features downstream from the initial photoexcitation, such as single-versus two-electron transfer processes, [3b] proton transfer pathways,o rm ultiple concurrent reaction mechanisms,c an be elucidated by NMR spectroscopy. [3a] Furthermore,owing to its high-resolution spectra, NMR spectroscopy provides detailed structural information about intermolecular interactions [4] and aggregation, revealing key information of activation or deactivation of substrates or catalysts in photocatalysis. [5] However,b esides the limited time resolution, NMR spectroscopy faces the additional challenge that singleelectron transfer (SET) processes,w hich are typical for photocatalysis,c ause an interplay of paramagnetic and diamagnetic species.O ften, the lifetime of these paramagnetic radical intermediates is so short that they do not even affect the NMR spectra of the diamagnetic species.T he information on these transient radicals can often be accessed only by photo-chemically induced dynamic nuclear polarization (photo-CIDNP) through their diamagnetic recombination and disproportionation products. [3b,6] In contrast, stable long-lived radicals can impose severe challenges to NMR spectroscopy.W hile in the case of several i...

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Photo-induced radical polarization and liquid-state dynamic nuclear polarization using fullerene nitroxide derivatives

Cited by 29 publications

References 32 publications

Viscosity effects on optically generated electron and nuclear spin hyperpolarization

Viscosity effects on optically generated electron and nuclear spin hyperpolarization

Combined In Situ Illumination‐NMR‐UV/Vis Spectroscopy: A New Mechanistic Tool in Photochemistry

Combined In Situ Illumination‐NMR‐UV/Vis Spectroscopy: A New Mechanistic Tool in Photochemistry

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