Electrostatic Bubbles and Supramolecular Assistance of Photosensitization by Carboxylated Ru(II) Complexes
Notice bibliographique
Résumé
The paper examines the supramolecular effects at play during photosensitization by carboxylated Ru(II) sensitizers, both by experiment and by modeling. Experimentally, twelve Ru(II) complexes of pyrazolylpyridine and polypyridine ligands, including two benchmark complexes and two new species, were assessed as photosensitizers by measurement of the kinetics of methyl viologen cation radical (MV(*)(+)) generation through an oxidative, photoinduced electron transfer (PET) to methyl viologen (MV(2+)) under continuous irradiation in the presence of a sacrificial reductant. All complexes, luminescent or not, produced measurable amounts of MV(*)(+) in CH(3)CN. The assessment protocol was found to be useful with sensitizers of widely varying excited-state lifetimes (tau) as well as being easier and faster than conventional approaches. The seven sensitizers bearing peripheral COOH groups were found to be significantly more active than their non-carboxylated analogues, which is consistent with ionization of the COOH groups and electrostatic promotion of PET. Only the luminescent complexes were active in aqueous solvents, where tau appears to be the dominant effector. The benefits are exemplified by the singly carboxylated [Ru(H1)(bpy)(2)](2+) (H1 is 1-(4-carboxyphenyl)-3-(2-pyridyl)-4,5,6,7-tetrahydroindazole), a weakly luminescent sensitizer that was less active in aqueous solvents than [Ru(bpy)(3)](2+) (bpy is 2,2'-bipyridine), but which became the better sensitizer in CH(3)CN. Computationally, electrostatic field and dissociation energy calculations demonstrated that even a single peripheral COO(-) substituent suffices to provide supramolecular assistance: it defines a spheric "bubble" of electrostatically attractive space that is sufficiently large to allow the supramolecular preassociation of MV(2+), which provides an entropic advantage to PET that reduces the importance of tau in organic solvent. Calculations also show that the PET is electrostatically favored over its reverse (BET) even with cationic sensitizers because the "bubble" contracts after PET while the bulk medium becomes more repulsive, and favorable cation exchanges can occur to effect post-PET dissociation. Two peripheral COO(-) groups can define a two-point binding site for MV(2+) in an attractive sector of space that contracts to a kidney-shaped "bubble" after PET. This enables unimolecular PET while the reverse reaction remains bimolecular. The resultant benefits are illustrated with [Ru(Na1)(2)(bpy)](2+), a very weakly luminescent sensitizer that was totally inactive in H(2)O but appreciably active in CH(3)CN, despite the need to displace Na(+) in order to derive any electrostatic benefit. The Marcus free energies of activation for PET and BET corroborate the benefits of carboxylation, solvent, and other factors and correlated with the experimental rate constants.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».