1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 Combining Zinc Phthalocyanines, Oligo(p- Phenylenevinylenes), and Fullerenes to Impact Reorganization Energies and Attenuation Factors Marcel Krug, [a] Christina Stangel, [b, c] Anna Zieleniewska, [a] Timothy Clark, [a] Tomás Torres, [d, e] Athanassios G. Coutsolelos,* [b] and Dirk M. Guldi* [a] A study on electron transfer in three electron donor-acceptor complexes is reported. These architectures consist of a zinc phthalocyanine (ZnPc) as the excited-state electron donor and a fullerene (C 60 ) as the ground-state electron acceptor. These complexes are brought together by axial coordination at ZnPc. The key variable in our design is the length of the molecular spacer, namely, oligo-p-phenylenevinylenes. The lack of appre- ciable ground-state interactions is in accordance with strong excited-state interactions, as inferred from the quenching of ZnPc centered fluorescence and the presence of a short-lived fluorescence component. Full-fledged femtosecond and nano- second transient absorption spectroscopy assays corroborated that the ZnPc · + -C 60 ·  charge-separated state formation comes at the expense of excited-state interactions following ZnPc photoexcitation. At a first glance, the ZnPc · + -C 60 ·  charge- separated state lifetime increased from 0.4 to 86.6 ns as the electron donor-acceptor separation increased from 8.8 to 29.1 Å. A closer look at the kinetics revealed that the changes in charge-separated state lifetime are tied to a decrease in the electronic coupling element from 132 to 1.2 cm 1 , an increase in the reorganization energy of charge transfer from 0.43 to 0.63 eV, and a large attenuation factor of 0.27 Å 1 . 1. Introduction The increasing demand for clean inexhaustible energy resources renders solar energy one of the most compelling future solutions. [1] In natural photosynthesis, solar light is harnessed and stored in chemically useful products by a cascade of light- induced energy and electron transfer reactions in self-organized pigments. [2] To this end, extensive efforts have been devoted to develop simpler artificial photosynthetic systems exhibiting charge separation for efficient conversion of solar energy into electric and chemical energies. [3] Interfacing electron donors and acceptors with π-conju- gated bridges acting as molecular wires creates an exceptional class of photosynthetic model systems. [4] Furthermore the electronic properties of these materials render them potentially useful for technological applications ranging from molecular electronics to solar energy conversion. [5] The nature of the linker between the two moieties controls the orientation, distance, as well as the electronic coupling and, in turn, small structural variations can impact on the lifetime of the charge-separated state. [3h,4,6,7] It has been shown that the π-conjugated bridge in electron donor-acceptor assemblies has a profound impact on the rates of photoinduced charge-transfer. [4,8] Moreover, the π-conju- gated bridge affects the mechanism, by which charge transfer occurs, namely coherent tunneling versus incoherent hopping mechanism. [4,9] Tunneling is described by the superexchange model, which requires the electron donors and acceptors electronic states to be energetically well separated from the states of the π-conjugated bridge and the latter has the role of a coupling medium for the charge transfer process. The incoherent hopping mechanism, which is also referred to a thermally activated hopping mechanism involves real inter- mediate states located at the bridge to transport the hole or the electron. [9] (Metallo)porphyrins (MP) and (metallo)phthalocyanines (MPc), which serve the dual roles of light harvester and electron donor, stand out due to their large absorption cross section across the visible range of the solar spectrum, their ease of synthesis, and their marked stability. [10] Changing the metal and peripheral substituents enables control over the resulting physico-chemical properties. [11] Fullerenes, in general, and C 60 , in particular are promising electron acceptors, [3k,12] since they can accept up to six electrons due to their low-energy, triply degenerated LUMOs. [13] Of even bigger relevance is their small reorganization energy (λ) in charge transfer, due to their spherical structure: Fast charge separation and slow charge recombination, which are placed in the normal region of the [a] M. Krug, A. Zieleniewska, Prof. Dr. T. Clark, Prof. Dr. D. M. Guldi Department of Chemistry and Pharmacy, Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität Erlangen-Nuernberg, Egerlandstr. 3, 91058 Erlangen, Germany E-mail: dirk.guldi@fau.de [b] C. Stangel, Prof. Dr. A. G. Coutsolelos Department of Chemistry, University of Crete, Laboratory of Bioinorganic Chemistry, Voutes Campus, 71003 Heraklion, Crete, Greece E-mail: acoutsol@uoc.gr [c] C. Stangel Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, Athens 11635, Greece [d] Prof. Dr. T. Torres IMDEA-Nanociencia, C/Faraday, 9, Cantoblanco, 28049 - Madrid, Spain [e] Prof. Dr. T. Torres Institute for Advanced Research in Chemical Sciences (IAdChem), Universidad Autónoma de Madrid, 28049 Madrid, Spain Supporting information for this article is available on the WWW under https://doi.org/10.1002/cphc.201900780 Articles DOI: 10.1002/cphc.201900780 1 ChemPhysChem 2019, 20, 1 – 11 © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! ��