The magnetic-field dependence of the cage escape efficiency (phi(ce)) of [Ru(bpy)(3)](3+) and methyl viologen radicals (MV+.) from the primary redox pair formed upon quenching of photoexcited [Ru(bpy)(3)](2+) by MV2+ was measured by laser flash spectroscopy in aqueous solution as a function of the magnetic field (0-2.85 T) in the temperature range from 5 to 69 degreesC. Furthermore, the H-1 NMR T-1 times of the paramagnetic [Ru(bpy)(3)](3+) were measured between -40 and 42 degreesC. The kinetic data were analyzed in terms of a kinetic model that takes into account spin conservation in the forward reaction between the (MLCT)-M-3 state of [Ru(bpy)(3)](2+) and the electron acceptor MV2+ yielding a triplet spin-correlated radical pair (RP) and the in-cage backward electron transfer requiring singlet character of the RP. The triplet-to-singlet spin conversion of the geminate RP is explicitly treated by the stochastic Liouville equation formalism. By theoretical simulation of the observed magnetic field dependence of phi(ce), the temperature dependent absolute values of the rate constants k(ce) (cage escape), k(bet) (backward electron transfer in singlet RPs), and k(TS) (magnetic-field independent triplet-to-singlet interconversion) could be assessed. The temperature dependence of k(ce) exhibits a very good proportionality to the solvent viscosity. The values obtained for k(TS) are in good agreement with the results on the electron spin relaxation time of [Ru(bpy)(3)](3+) derived by the Solomon relation from the H-1 NMR T-1 times. The effective rate of backward electron transfer in the geminate RP turns out to be close to spin-controlled, i.e., it is determined by the rate constant k(TS) of the triplet-singlet spin conversion process. The true rate constant k(bet), varying from 5.5 x 10(10) s(-1) to 1.2 x 10(11) s(-1), is about seven times larger than the effective value for the total backward electron transfer comprising spin conversion and spin-allowed backward electron transfer.

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionSpin Chemical Control of Photoinduced Electron-Transfer Processes in Ruthenium(II)-Trisbipyridine-Based Supramolecular Triads J. Am. Chem. Soc.1999, 121, 1076−1087Thomas Klumpp, Markus Linsenmann, Steven L. Larson, Bradford R. Limoges, Dieter Bürssner, Evgenii B. Krissinel, C. Michael Elliott, and Ulrich E. SteinerCite this: J. Am. Chem. Soc. 1999, 121, 16, 4092Publication Date (Web):April 8, 1999Publication History Published online8 April 1999Published inissue 1 April 1999https://pubs.acs.org/doi/10.1021/ja995507shttps://doi.org/10.1021/ja995507scorrectionACS PublicationsCopyright © 1999 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views341Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (13 KB) Get e-Alertsclose Get e-Alerts

Nanosecond time-resolved absorption studies in a magnetic field ranging from zero to 3.0 T have been performed on a series of covalently linked donor-Ru(bipyridine)(3)-acceptor complexes (D-C2+-A(2+)). In these complexes the electron donor is a phenothiazine moiety linked to a bipyridine by a (-CH2-)(p) (p = 1, 4, 5, 7) chain, and the electron acceptor is an N,N'-diquaternary-2,2'-bipyridinium moiety, linked to a bipyridine by a (-CH2-)(2) chain. On the nanosecond time scale the first detectable photoinduced electron-transfer product after exciting the complex C2+ is the charge-separated (CS) state, D+-C2+-A(+), where an electron of the phenothiazine moiety, D, has been transferred to the diquat moiety, A(2+). In zero field the lifetime of the CS state is about 150 ns. At low fields (B-0 < 0.5 T) the magnetic field strongly affects the decay kinetics, splitting it up into a major component, the rate constant of which decreases by a factor of about 10 at fields of several 100 mT, and a minor component with an approximately field independent rate constant. At high fields (B-0 > 0.5 T) the total amplitude of the CS absorption signal decreases and the relative contribution of the fast decaying component increases. The magnetic field effects can be consistently interpreted and quantitatively modeled by taking into account the mechanisms and kinetics of the spin multiplicity changes in the CS state and its precursor, a short-lived CT state (D-C3+-A(+)) formed upon primary electron transfer from the triplet excited complex to the diquat moiety, Exploiting the magnetic field dependent kinetics, the rate constants of the triplet-singlet transitions in the two types of linked radical pairs and of all the electron-transfer processes following the primary one can be assessed. Magnetic-field-dependent investigations thus can be essential for the understanding of the complex kinetics in supramolecular systems with sequential cyclic electron transfer.

Hydrogen-free amorphous carbon films produced by direct deposition of low energy carbon ions exhibit diamond-like properties such as extreme hardness, large band gap and high index of refraction. Using mass separated ion beam deposition, high purity diamond-like carbon (DLC) films were grown under vacuum conditions better than 10−5 Pa on Si substrates kept at room temperature. The deposition parameters such as the ion energy, vacuum conditions, substrate temperature and ion species can be controlled independently, and thus used to modify the film properties and composition. In this paper we present the first results of doping of DLC films during growth by alternating deposition of 100 eV 12C+ ions and dopant ions such as 63Cu+, 27Al+, 11B+ or 14N+. For beam currents of up to 100 μA cm−2, DLC films with a thickness of several micrometers were produced. Undoped films were characterized by Raman spectrometry, ellipsometry, electrical measurements, Rutherford backscattering spectrometry (RBS) and proton induced X-ray emission. For these films an energy gap of 2.6 eV, a Vickers hardness of 4500 kg mm−2, an index of refraction n > 2, a resistivity of 109 Ω cm and an electrical breakdown strength greater than 109 V m−1 were measured. Dopant concentration profiles of copper-doped films were analyzed by RBS. Homogeneous dopant concentrations of several atomic per cent are easily achieved.