German Edition: DOI: 10.1002/ange.201706564 Molecular Dyads International Edition: DOI: 10.1002/anie.201706564 Time-Resolved Interception of Multiple-Charge Accumulation in a Sensitizer–Acceptor Dyad StØphanie Mendes Marinho, Minh-Huong Ha-Thi,* Van-Thai Pham, Annamaria Quaranta,* Thomas Pino, Christophe Lefumeux, Thierry ChamaillØ, Winfried Leibl, and Ally Aukauloo* Abstract: Biomimetic models that contain elements of photo- synthesis are fundamental in the development of synthetic systems that can use sunlight to produce fuel. The critical task consists of running several rounds of light-induced charge separation, which is required to accumulate enough redox equivalents at the catalytic sites for the target chemistry to occur. Long-lived first charge-separated state and distinct electronic signatures for the sequential charge accumulated species are essential features to be able to track these events on a spectroscopic ground. Herein, we use a double-excitation nanosecond pump–pump–probe experiment to interrogate two successive rounds of photo-induced electron transfer on a molecular dyad containing a naphthalene diimide (NDI) linked to a [Ru(bpy) 3 ] 2+ (bpy = bipyridine) chromophore by using a reversible electron donor. We report an unprecedented long-lived two-electron charge accumulation (t = 200 ms). Molecular complexes as mimics for artificial photosynthesis need to undergo several rounds of directional light-induced charge separation to accumulate enough redox equivalents at the catalytic sites where bonds are broken and/or made. A critical step to efficiently photoactivate a catalyst is the time matching of light absorption by the photosensitizer, occurring by single photon events, with multicharge chemical reactions that occur at the catalytic site. In Photosystem II (PSII), each photon excitation of the P 680 chromophore triggers a series of five electron-transfer steps through topologically ordered redox stations that leads to a very efficient (> 90 %) charge- separation state, (CaMn 4 ) + /Q B  . This species is stable for tens of seconds at room temperature, [1] enabling the study of multiple turnover with pump–probe transient-absorption techniques. [2] On the contrary, molecular models mimicking Photosystem II are quite minimalist and are, for the majority, constituted of a photosensitizer and a catalytic unit. [3] Such artificial systems are not as efficient as the natural system and it is challenging to probe multiple-electron transfer. To date, only a few reports have addressed the question of deciphering the stepwise process of charge accumulation in artificial systems. [4] The results of such investigations could allow chemists to optimize the coupling of multielectronic catalysis to light-induced one-electron transfer as recently discussed in a review by Hammarstrçm. [5] In this study, we have chosen a molecular dyad containing a naphthalenediimide (NDI) moiety that can act as a rever- sible reservoir for two electrons linked to a [Ru(bpy) 3 ] 2+ chromophore (Scheme 1), abbreviated as Ru-NDI. The syn- thesis and characterization of Ru-NDI have been reported previously. [6] The reasons for this choice are: 1) both the singly and doubly reduced states of the NDI fragment are thermo- dynamically accessible from the reduced state of the chro- mophore, the formal Ru I species; however, a non-negligible drop in the driving force occurs (DG = 670 meV for NDIC  versus DG = 320 meV for NDI 2 ) ; 2) the distinctive spectral features associated with Ru-NDI and the singly and doubly reduced forms of NDI, namely a sharp peak (e  26 000 m 1 cm 1 ) at  484 nm accompanied by prominent shoulders at approximately 510 and 620 nm for NDIC  , and a sharp peak (e  26 000 m 1 cm 1 ) centered at 410 nm for doubly reduced NDI 2 . [7] Importantly, the study was con- ducted in the presence of a reversible external electron donor. Scheme 1. Molecular structure of [Ru-NDI] 2+ . [*] S. Mendes Marinho, Prof. A. Aukauloo Institut de Chimie MolØculaire et des MatØriaux d’Orsay (ICMMO) UniversitØ Paris Sud, CNRS 91405 Orsay Cedex (France) E-mail: ally.aukauloo@u-psud.fr Dr. M.-H. Ha-Thi, Dr. V.-T. Pham, Dr. T. Pino, C. Lefumeux, T. ChamaillØ Institut des Sciences MolØculaire d’Orsay (ISMO), CNRS Univ Paris Sud, UniversitØ Paris-Saclay 91405 Orsay (France) E-mail: minh-huong.ha-thi@u-psud.fr Dr. V.-T. Pham Present address: MAX IV Laboratory, Lund University P.O. Box 118, 22100 Lund (Sweden) Dr. V.-T. Pham Center for Quantum Electronics, Institute of Physics, Vietnam Academy of Science and Technology P.O. Box 429, Boho, 10000 Hanoi (Vietnam) Dr. A. Quaranta, Dr. W. Leibl, Prof. A. Aukauloo Institute for integrative Biology of the Cell (I2BC), CEA, CNRS UniversitØ Paris-Saclay, UMR 9198 91191 Gif-sur-Yvette (France) E-mail: annamaria.quaranta@cea.fr Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.org/10.1002/anie.201706564. A ngewandte Chemi e Communications 1 Angew. Chem. Int. Ed. 2017, 56,1–6  2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! Ü Ü