Mechanism of the photodissociation of 4-diphenyl( trimethylsilyl)methyl-N,N-dimethylaniline
Loading...
Date
Authors
Tasis, D. A.
Siskos, M. G.
Zarkadis, A. K.
Steenken, S.
Pistolis, G.
Journal Title
Journal ISSN
Volume Title
Publisher
American Chemical Society
Abstract
Type
Type of the conference item
Journal type
peer reviewed
Educational material type
Conference Name
Journal name
Journal of Organic Chemistry
Book name
Book series
Book edition
Alternative title / Subtitle
Description
On irradiation in hexane (248- and 308-nm laser light) 4-diphenyl(trimethylsilyl)methyl-N,N-dimethylaniline, undergoes photodissociation of the C-Si bond giving 4-N,N-dimethylamino-triphenylmethyl radical, 3(.) (lambda(max) at 343 and 403 nm), in very high quantum yield (Phi = 0.92). The intervention of the triplet state of 2 (lambda(max) at 515 nm) is clearly demonstrated through quenching experiments with 2,3-dimethylbuta-1,3-diene, styrene, and methyl methacrylate using nanosecond laser flash photolysis (LFP). The formation of 3(.) is further demonstrated using EPR spectroscopy. The detection of the S-1 state of 2 was achieved using 266-nm picosecond LFP, and its lifetime was found to be 1400 ps. in agreement with the fluorescence lifetime (tau(f) = 1500 ps, Phi(f) = 0.085). The S-1 state is converted almost exclusively to the T-1 state (Phi T = 0.92). In polar solvents such as MeCN, 2 undergoes (1) photoionization to its radical cation 2(.+), and (2) photodissociation of the C-Si bond, giving radical 3(.) as before in hexane. The formation of 2(.+) occurs through a two-photon process. Radical cation 2(.+) does not fragment further, as would be expected, to 3(.) via a nucleophile(MeCN)assisted C-Si bond cleavage but regenerates the parent compound 2. Obviously, the bulkiness of the triphenylmethyl group prevents interaction of 2(.+) with the solvent (MeCN) and transfer to it of the electrofugal group Me3Si+. The above results of the laser flash photolysis are supported by pulse radiolysis, fluorescence measurements, and product analysis.
Description
Keywords
laser flash-photolysis, nucleophile-assisted cleavage, silicon bond-cleavage, radical cations, methyl-methacrylate, aqueous-solution, carbon-carbon, aromatic-amines, photochemistry, fragmentation
Subject classification
Citation
Link
<Go to ISI>://000088261900006
http://pubs.acs.org/doi/pdfplus/10.1021/jo000023w
http://pubs.acs.org/doi/pdfplus/10.1021/jo000023w
Language
en
Publishing department/division
Advisor name
Examining committee
General Description / Additional Comments
Institution and School/Department of submitter
Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας