Combination of illumination and high resolution NMR spectroscopy: Key features and practical aspects, photochemical applications, and new concepts

Nitschke, Philipp; Lokesh, N.; Gschwind, Ruth M.

doi:10.1016/j.pnmrs.2019.06.001

Cited by 60 publications

(57 citation statements)

References 145 publications

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“…We found that S dramatically increase in the order: 1 < 2 < 3. The superior water solubility of compound 3 allowed us to carry out successfully photo-NMR 44 investigations by in situ illumination, which, for pH < pK MS a , corroborated the nearly quantitative conversion of MCH into an achiral species displaying a cis-non-coplanar conformation (cis-MCH) (see ESI † for a more detailed discussion). Interestingly, UV-Vis studies revealed that all pK MS a values fall within the range 1.7-3.2 as proposed by Liao 5 and, as observed for pK c , progressively increase as a function of n. These results further conrm the interplay between the EWG effect of the sulfonate group and the length of the alkyl bridge in determining the thermodynamics.…”

Section: Comparative Evaluationmentioning

confidence: 70%

Thermodynamics and kinetics of protonated merocyanine photoacids in water

et al. 2020

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Section: Comparative Evaluationmentioning

confidence: 70%

Thermodynamics and kinetics of protonated merocyanine photoacids in water

et al. 2020

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“…The fact that the fluorination source (Selectfluor ® ) and light sources (generally 365-420 nm LEDs or CFL bulbs) are common themes but that different PSCats are optimal in different reactions suggests that the substrates themselves may play a role in the precomplexation with Selectfluor ® and the PSCat in order to module the UV-visible absorption or T 1 energies [235,236]. Such behavior has been observed in other photochemical reactions [237,238].…”

Section: Mechanistic Understanding and Precomplexationmentioning

confidence: 99%

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

Yakubov

Barham

2020

Beilstein J. Org. Chem.

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The importance of fluorinated products in pharmaceutical and medicinal chemistry has necessitated the development of synthetic fluorination methods, of which direct C–H fluorination is among the most powerful. Despite the challenges and limitations associated with the direct fluorination of unactivated C–H bonds, appreciable advancements in manipulating the selectivity and reactivity have been made, especially via transition metal catalysis and photochemistry. Where transition metal catalysis provides one strategy for C–H bond activation, transition-metal-free photochemical C–H fluorination can provide a complementary selectivity via a radical mechanism that proceeds under milder conditions than thermal radical activation methods. One exciting development in C–F bond formation is the use of small-molecule photosensitizers, allowing the reactions i) to proceed under mild conditions, ii) to be user-friendly, iii) to be cost-effective and iv) to be more amenable to scalability than typical photoredox-catalyzed methods. In this review, we highlight photosensitized C–H fluorination as a recent strategy for the direct and remote activation of C–H (especially C(sp3)–H) bonds. To guide the readers, we present the developing mechanistic understandings of these reactions and exemplify concepts to assist the future planning of reactions.

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“…For monitoring the photochromism of PpFABLA (1), a different analytical method is required, in which the acquisition of data does not interfere with the light used for excitation and is found in in-situ irradiation NMR spectroscopy [30][31][32] . An isotropic solution of PpFABLA (1) in TCE-d 2 is measured by timeresolved 19 F NMR spectroscopy while being irradiated using the same LEDs already used for excitation of the UV-vis samples (Figure 2).…”

Section: Switching the Secondary Structurementioning

confidence: 99%

Light-Controlled Lyotropic Liquid Crystallinity of Polyaspartates

Hirschmann

Thiele²

2021

Preprint

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In nature, proteins like rhodopsin act as transducer for photo-chemical reactions causing biological responses (e.g. enabling vision). The underlying concept – a photo-induced conformational change of the protein as amplifier of the photo-responsive moiety – can also be adopted by synthetical polymers or foldamers that have the propensity to form ordered secondary structures (e.g. polypeptides). An alternative approach to amplify photo-chemical responses is their incorporation into liquid crystals. With only a few exceptions, photo-insensitive liquid crystals are doped with dyes that favour disorder upon irradiation. In theory, photo-responsive polypeptides, capable of forming lyotropic liquid crystals, could exploit both amplification approaches but, in practice, their photo-responsivity is hampered by the reduced mobility of polypeptides in concentrated solutions. Here we show that the E/Z photo-isomerisation of an azobenzene containing polyaspartate initiates a helix-coil backbone transition, which reversibly alters the polypeptide solution from anisotropic to isotropic. In contrast to other photo-responsible polymers14, in which thermal relaxation to the more stable photo-isomer is quite fast, both photo-isomers are thermally stable and interconvertible by visible light in a single solvent. Local irradiation and magnetic fields lead to spatial resolution and unidirectional architectures of the liquid crystal, respectively. Our results demonstrate that photo-isomerisation on a molecular level is amplified in three stages via intra- and intermolecular interactions to yield a unidirectional, chiral liquid crystal. We believe, the morphological changes of the liquid crystal induced by light will facilitate a multitude of applications, like photo-alignment or the photo-control of solution viscosity and anisotropic diffusion. When incorporated into layer-by-layer architectures the polymer could find application in biomedicine and the spatial and temporal resolution could be exploited in nano-technology.

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Combination of illumination and high resolution NMR spectroscopy: Key features and practical aspects, photochemical applications, and new concepts

Cited by 60 publications

References 145 publications

Thermodynamics and kinetics of protonated merocyanine photoacids in water

Thermodynamics and kinetics of protonated merocyanine photoacids in water

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

Light-Controlled Lyotropic Liquid Crystallinity of Polyaspartates

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