Transient Kinetics and Quantum Yield Studies of Nanocrystalline α‑Phenyl-Substituted Ketones: Sorting Out Reactions from Singlet and Triplet Excited States

• Published in: Journal of the American Chemical Society Vol. 140; no. 26; pp. 8192 - 8197
• Main Authors: Park, Jin H, Chung, Tim S, Hipwell, Vince M, Rivera, Edris, Garcia-Garibay, Miguel A
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 05.07.2018; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Physical Sciences; Science & Technology; RADICAL PAIRS; ORGANIC-SYNTHESIS; ENANTIOSPECIFIC SYNTHESIS; MAGNETIC-FIELD; PHOTODECARBONYLATION; PHOTOCHEMICAL-REACTIONS; QUATERNARY CENTERS; SOLID-STATE; CRYSTALLINE SOLIDS; LASER-FLASH-PHOTOLYSIS
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.8b03247

Recent work has shown that diarylmethyl radicals generated by pulsed laser excitation in nanocrystalline (NC) suspensions of tetraarylacetones constitute a valuable probe for the detailed mechanistic analysis of the solid-state photodecarbonylation reaction. Using a combination of reaction quantum yields and laser flash photolysis in nanocrystalline suspensions of ketones with different substituents on one of the α-carbons, we are able to suggest with confidence that a significant fraction of the initial α-cleavage reaction takes place from the ketone singlet excited state, that the originally formed diarylmethyl-acyl radical pair loses CO in the crystal with time constants in the sub-nanosecond regime, and that the secondary bis­(diarylmethyl) triplet radical pair has a lifetime limited by the rate of intersystem crossing of ca. 70 ns.