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Article Dans Une Revue Journal of the American Chemical Society Année : 2022

Selective and Cooperative Photocycloadditions within Multistranded Aromatic Sheets

Résumé

A series of aromatic helix-sheet-helix oligoamide foldamers composed of several different photosensitive diazaanthracene units have been designed and synthesized. Molecular objects up to 7 kDa were straightforwardly produced on a 100 mg scale. NMR and crystallographic investigations revealed that helix-sheet-helix architectures can adopt one or two distinct conformations. Sequences composed of an even number of turn units were found to fold in a canonical symmetrical conformation with two helices of identical handedness stacked above and below the sheet segment. Sequences composed of an odd number of turns revealed a coexistence between a canonical fold with helices of opposite handedness, and an alternate fold with a twist within the sheet and two helices of identical handedness. The proportions between these species could be manipulated, in some cases quantitatively, being dependent on solvent, temperature and absolute control of helix handedness. Diazaanthracene units were shown to display distinct reactivity towards 4+4 photocycloadditions according to the substituent in the 9 position. Their organization within the sequences was programmed to allow photoreactions to take place in a specific order. Reaction pathways and kinetics were deciphered and products characterized, demonstrating the possibility to orchestrate successive photoreactions so as to avoid orphan units, or to deliberately produce orphan units at precise locations. Strong cooperative effects were observed in which the photoreaction rate was influenced by the presence (or absence) of photoadducts in the structure. Multiple photoreactions within the aromatic sheet eventually lead to the structure lengthening and stiffening, locking conformational equilibria. Photoproducts could be thermally reverted.
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Dates et versions

hal-03767630 , version 1 (02-09-2022)

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Bappaditya Gole, Brice Kauffmann, Arnaud Tron, Victor Maurizot, Nathan Mcclenaghan, et al.. Selective and Cooperative Photocycloadditions within Multistranded Aromatic Sheets. Journal of the American Chemical Society, 2022, 144 (15), pp.6894-6906. ⟨10.1021/jacs.2c01269⟩. ⟨hal-03767630⟩
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