Issue 3, 2002

Photoreduction of trans-4-R-4′-nitrostilbenes with R: OMe, H and NO2 by di- and trialkylamines in polar media

Abstract

The photoinduced reactions of trans isomers of 4-nitrostilbene (1), 4,4′-dinitrostilbene (2), and 4-methoxy-4′-nitrostilbene (3) as well as a nitrostilbazolium salt (4) by DABCO, diethylamine (DEA) and triethylamine (TEA) in acetonitrile and mixtures with water were studied by pulsed (λexc = 354 nm) and steady-state (λirr = 366 nm) photolysis. The rate constant for quenching of the triplet states of 13 in acetonitrile by TEA is kq = 1 × 108 M−1 s−1 and is significantly smaller in the presence of water. Quenching the triplet states of 13 by DABCO is more efficient and kq of 4 in acetonitrile is close to the diffusion-controlled limit. The subsequent transient of 13 in the presence of the tertiary aliphatic amines is ascribed to the radical anion. With TEA (or DEA) the conjugate acid of the radical anions with maxima at 400–500 nm are generated (via the α-aminoethyl radical) in a secondary step. Only for 2 do the spectra of the two radicals absorb differently. The radical intermediates subsequently undergo a termination reaction yielding (partly) the corresponding nitroso compounds and eventually arylhydroxylamines. The maximum quantum yield of decomposition of 14 in the presence of TEA (0.3 M) is 0.1–0.4. Solvent separated ion pairs for 13, in contrast to 4, were observed by conductivity measurements. The charges of 13 remain separated for times which are comparable or longer than the half-lives of the radicals. The mechanisms of the two subsequent reduction reactions are discussed.

Article information

Article type
Paper
Submitted
10 Sep 2001
Accepted
27 Nov 2001
First published
04 Jan 2002

Phys. Chem. Chem. Phys., 2002,4, 482-489

Photoreduction of trans-4-R-4′-nitrostilbenes with R: OMe, H and NO2 by di- and trialkylamines in polar media

H. Görner, Phys. Chem. Chem. Phys., 2002, 4, 482 DOI: 10.1039/B108192F

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements