Issue 7, 2010
From the journal:

Physical Chemistry Chemical Physics

Helquats, helical extended diquats, as fast electron transfer systems†

Lubomír Pospíšil,*ab   Filip Teplý,b   Miroslav Gál,a   Louis Adriaenssens,b   Michal Horáčeka  and  Lukáš Severab  

* Corresponding authors

a J. Heyrovský Institute of Physical Chemistry, v.v.i., Academy of Sciences of the Czech Republic, Dolejškova 3, 18223 Prague, Czech Republic
E-mail: lubomir.pospisil@jh-inst.cas.cz
Fax: +420-286582307
Tel: +420-266053197

b Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i., Flemingovo n. 2, Prague, Czech Republic
E-mail: teply@uochb.cas.cz
Fax: +420-220183578
Tel: +420-220183415

Abstract

Helicene-viologen structural hybrids, like [5]helquat, 6,7,10,11-tetrahydrodipyrido[2,1-a:1′,2′-k][2,9]phenanthrolinediium, and its four methylated derivatives, are characterized by electrochemical admittance and EPR spectroscopy. All compounds are reversibly reduced in two one-electron steps. Formal redox potentials correlate with the calculated LUMO energies. The electron transfer is coupled with a weak adsorption of the reactants. The analysis of the frequency dependence of the electrode admittance is used for the separation of Faradaic and double layer contributions and finally to the estimation of heterogeneous rate constants. Heterogeneous rate constants determined this way are in the range 0.1 to 3 cm s−1. In all cases the second electron transfer is faster than the first redox step by a factor of three. The Frumkin correction for the acceleration by the double layer potential further amplifies this difference. The heterogeneous rate constants of derivatives correlate with the solvent reorganization energy estimated from the Marcus model. EPR spectra confirm the radical cation formation. The radical of [5]helquat participates in an extremely fast self-exchange process with the parent dication characterized by the self-exchange rate constant kET = (2.4 ± 0.5) × 109 M−1 s−1.

Graphical abstract: Helquats, helical extended diquats, as fast electron transfer systems

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Article information

DOI
https://doi.org/10.1039/B915148F
Article type
Paper
Submitted
27 Jul 2009
Accepted
01 Dec 2009
First published
11 Jan 2010

Phys. Chem. Chem. Phys., 2010,12, 1550-1556

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Helquats, helical extended diquats, as fast electron transfer systems

L. Pospíšil, F. Teplý, M. Gál, L. Adriaenssens, M. Horáček and L. Severa, Phys. Chem. Chem. Phys., 2010, 12, 1550 DOI: 10.1039/B915148F

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