- Bright Electrochemiluminescence Tunable in the Near-Infrared of Chiral Cationic Helicene Chromophores
Haidong Li, Antoine Wallabregue, Catherine Adam, Géraldine Maria Labrador Beltran, Johann Bosson, Laurent Bouffier, Jerome Lacour, Neso Sojic
J. Phys. Chem. C 2017, 121, 785-792
A selection of cationic  and helicenes are studied for their electrochemical, fluorescence and electrochemiluminescence (ECL) properties in acetonitrile solutions. Their photophysical and redox responses are drastically tuned by the introduction of auxochrome substituents at their periphery or the interconversion of oxygen and nitrogen atoms within the helical core. All diaza helicenes exhibit a reversible reduction process whereas, in the presence of oxygen instead of nitrogen atoms in the helical core, irreversible oxidations and a decrease of ECL intensity are observed. ECL emission was successfully produced with two sacrificial co-reactants (benzoyl peroxide and tri-n-propylamine, TPrA). Helicene DMQA+, helicene DIAZA(Pr/Br)+ and DIAZA(Hex/Br)+ exhibit similar ECL emission wavelength in the near-infrared region and generates very intense ECL signals. Their ECL efficiencies are up to 2.6 times higher than that of the reference compound [Ru(bpy)3]2+ when using TPrA as co-reactant. A thermodynamic map gathering both oxidation and reduction potentials and fluorescence data is proposed for the prediction of energy sufficiency needed in both co-reactant ECL systems. Such a systematic overview based on the photophysical and electrochemical properties may guide the conception and the synthesis of new chromophores with a strong ECL proficiency.
The authors have been alerted to an error in the reported values of the electrochemical potentials. In Figures 2 and 4 as well as in Table 1, the potentials of the helicene derivatives were mistakenly given versus the ferrocene/ferrocenium (Fc/Fc+) internal reference instead of a Ag wire pseudoreference. The Fc/Fc+ redox couple exhibits an oxidation potential value of 0.42 V vs Ag. Correspondingly, all of the potential values in the main text (six occurrences on page 787) are referenced versus Ag and not versus Fc/Fc+. Correct versions of Table 1 and Figures 2 and 4 are provided. This correction reinforces the validity of the conclusions of the presented ECL approach. It does not change the interpretation for the use of TPrA as the anodic coreactant (Figure 4), but the situation appears clearer now for DIAZA(Pr/Br)+5 and DIAZA(Hex/Br)+6 when using BPO as the cathodic coreactant. Indeed, in the original publication, both luminophores fell at the limit in the gray region (i.e., in the energy-deficient region where ECL should be forbidden) with BPO coreactant, whereas they gave unexpected ECL signals (with rather low ECL yields between 8.3 and 12.5%). With this correction, they now fall into the energy-sufficient region, which readily explains the ECL emission observed for both compounds. The authors sincerely apologize for this error and would like to thank Professor Bo W. Laursen from the University of Copenhagen, Denmark for drawing their attention to this matter.
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