Journal article
Singlet and Triplet Contributions to the Excited-State Activities of Dihydrophenazine, Phenoxazine, and Phenothiazine Organocatalysts Used in Atom Transfer Radical Polymerization
Journal of the American Chemical Society, Vol.143(9), pp.3613-3627
03/10/2021
DOI: 10.1021/jacs.1c00279
PMID: 33629835
Abstract
The photochemical dynamics of three classes of organic photoredox catalysts employed in organocatalyzed atom-transfer radical polymerization (O-ATRP) are studied using time-resolved optical transient absorption and fluorescence spectroscopy. The nine catalysts selected for study are examples of N-aryl and core-substituted dihydrophenazine, phenoxazine and phenothiazine compounds with varying propensities for control of polymerization outcomes. Excited singlet-state lifetimes extracted from the spectroscopic measurements are reported in N,N-dimethylformamide (DMF), dichloromethane (DCM), and toluene. Ultrafast (<200 fs to 3 ps) electronic relaxation of the photocatalysts after photoexcitation at near-UV wavelengths (318–390 nm) populates the first singlet excited state (S1). The S1-state lifetimes range from 130 ps to 40 ns with a considerable dependence on the photocatalyst structure and the solvent. The competition between ground electronic state recovery and intersystem crossing controls triplet state populations and is a minor pathway in the dihydrophenazine derivatives but is of greater importance for phenoxazine and phenothiazine catalysts. A comparison of our results with previously reported O-ATRP performances of the various photoredox catalysts shows that high triplet-state quantum yields are not a prerequisite for controlling polymer dispersity. For example, the photocatalyst 5,10-bis(4-cyanophenyl)-5,10-dihydrophenazine, shown previously to exert good polymerization control, possesses the shortest S1-state lifetime (135 ps in DMF and 180 ps in N,N-dimethylacetamide) among the nine examples reported here and a negligible triplet-state quantum yield. The results call for a re-evaluation of the excited-state properties of most significance in governing the photocatalytic behavior of organic photoredox catalysts in O-ATRP reactions.
Details
- Title: Subtitle
- Singlet and Triplet Contributions to the Excited-State Activities of Dihydrophenazine, Phenoxazine, and Phenothiazine Organocatalysts Used in Atom Transfer Radical Polymerization
- Creators
- Aditi Bhattacherjee - School of ChemistryMahima Sneha - School of ChemistryLuke Lewis-Borrell - School of ChemistryGiordano Amoruso - School of ChemistryThomas A.A Oliver - School of ChemistryJasper Tyler - School of ChemistryIan P Clark - Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton LaboratoryAndrew J Orr-Ewing - School of Chemistry
- Resource Type
- Journal article
- Publication Details
- Journal of the American Chemical Society, Vol.143(9), pp.3613-3627
- DOI
- 10.1021/jacs.1c00279
- PMID
- 33629835
- NLM abbreviation
- J Am Chem Soc
- ISSN
- 0002-7863
- eISSN
- 1520-5126
- Publisher
- American Chemical Society
- Grant note
- DOI: 10.13039/501100000266, name: Engineering and Physical Sciences Research Council, award: EP/ R012695/1, EP/L015366/1, EP/N509619/1; DOI: 10.13039/501100000288, name: Royal Society, award: UF1402310, URF\\R\\201007; DOI: 10.13039/100010665, name: H2020 Marie Sklodowska-Curie Actions, award: 793799; DOI: 10.13039/100011199, name: FP7 Ideas: European Research Council, award: 290966
- Language
- English
- Date published
- 03/10/2021
- Academic Unit
- Chemistry
- Record Identifier
- 9984216683402771
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