Volume 3, Issue 3, Pages 494-508 (September 2017) Aggregation-Induced Energy Transfer in a Decanuclear Os(II)/Ru(II) Polypyridine Light- Harvesting Antenna Dendrimer  Antonino Arrigo, Fausto Puntoriero, Giuseppina La Ganga, Sebastiano Campagna, Max Burian, Sigrid Bernstorff, Heinz Amenitsch  Chem  Volume 3, Issue 3, Pages 494-508 (September 2017) DOI: 10.1016/j.chempr.2017.06.002 Copyright © 2017 Elsevier Inc. Terms and Conditions

Chem 2017 3, 494-508DOI: (10.1016/j.chempr.2017.06.002) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 1 Representation of the Natural Photosynthetic Systems LH1 and LH2 and of the Energy Migration Patterns Occurring within the Overall Assembly RC is the reaction center in which charge separation takes place. The green rectangles within each light-harvesting multicomponent assembly are a single BChl chromophore. In LH2, the nine coplanar BChl units are omitted. Chem 2017 3, 494-508DOI: (10.1016/j.chempr.2017.06.002) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 2 Structural Formulae and Absorption Spectra (A) Structural formulae of the metal dendrimers discussed in this work. Counter-ions (hexafluorophosphate anions) are omitted. (B) A different representation of 1 (N-N stands for bpy; charge omitted). (C) The absorption spectra of 1–4 (concentration: 4 × 10−6 M) in acetonitrile. Chem 2017 3, 494-508DOI: (10.1016/j.chempr.2017.06.002) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 3 Luminescence Spectra and Energy Transfer Patterns in 1–4 (Top) Emission spectra of 1–4 in acetonitrile at room temperature, color code in agreement with the colors of the numbered compounds reported below the figure. Concentration is below 5 × 10−7 M for all the compounds. Excitation wavelength is 540 nm. The emission spectra to which we refer throughout the paper and shown in the figures are uncorrected for photomultiplier tube response; they are preferred over corrected spectra for better direct internal comparison, thus avoiding any possible source of errors caused by spectral correction; corrected emission spectra values are reported in the Supplemental Information and in the original references. (Bottom) Representation of the components Ru(II), Os(II), dpp, and bpy and schematization of compounds 1–4; the lower-energy excited states involve the different subunits shown, together with the downhill (or isoergonic) energy-transfer processes between subunits. More details are given in the Supplemental Information. Charges of compounds are omitted (formal charge is 20+ for 1 and 2 and 8+ for 3 and 4; counter-ions are PF6− anions). In 1 (extreme left), through-bond energy transfer from the peripheral units to the core, although thermodynamically allowed, has to overcome an energy barrier constituted by the intermediate higher-energy subunits. Direct through-space peripheral-to-core energy transfer is inefficient. Chem 2017 3, 494-508DOI: (10.1016/j.chempr.2017.06.002) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 4 Luminescence Spectral Changes of 1 upon Changing Concentration Emission spectra of 1 in acetonitrile with changing concentration show the red shift of the emission maximum with increasing concentration (top; color coded concentration as in the bottom panel). The emission maxima changes with concentration are shown in the bottom panel. The emission spectrum does not change significantly outside the concentration range reported in the figure. The emission spectrum of the highest-concentrated solution of 1 exhibits the same maximum as the emission spectrum of 3 (see Figure 3). The spectra are uncorrected for photomultiplier tube response and, compared with uncorrected spectra, are recorded under the same conditions. Corrected spectra for diluted and concentrated solutions of 1 are shown in the Supplemental Information. Chem 2017 3, 494-508DOI: (10.1016/j.chempr.2017.06.002) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 5 SAXS Experiments (A) SAXS experimental and calculated (by CRYSOL) data from concentrated samples (2.8 × 10−5 M) of 1 and 2 in acetonitrile, together with fits of the corresponding pair distance distribution functions (PDDF). (B) Distances between metal centers in 1 (green, distance between two metal centers connected by a dpp bridging ligand [e.g., Os(II) → intermediate Ru(II) centers]; red, distance between two metal centers having an interposed {(dpp)Ru(dpp)} unit [e.g., Os(II) → peripheral Ru(II) centers]; black, distance between two peripheral Ru(II) centers belonging to different dendrimer branches). Chem 2017 3, 494-508DOI: (10.1016/j.chempr.2017.06.002) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 6 Transient Absorption Spectroscopy Transient absorption spectra (left) and kinetics (right) of a 1.6 × 10−5 M acetonitrile solution of 1 (λexc: 400 nm, 100 fs pulse). In the left panel, the arrows indicate the isosbestic points retained during the process, occurring with a time constant of 18 ps. The kinetics of 1 at slower times (up to 3.2 ns) are shown in Figure S8. Chem 2017 3, 494-508DOI: (10.1016/j.chempr.2017.06.002) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 7 Global Decay Fittings of Transient Spectroscopy Data Global decay fitting of a concentrated (1.6 × 10−5 M) acetonitrile solution of 1 (λexc: 400 nm, 100 fs pulse), and decay-associated spectra, with their global fit coefficients. Chem 2017 3, 494-508DOI: (10.1016/j.chempr.2017.06.002) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 8 Pictorial Representation of the Energy Migration Processes Taking Place in 1, Indicating the Analogy with the Overimposed and Schematized LH2 Assemblies Intra-dendrimer energy transfer occurs with time constants lower than 1 ps (see Balzani et al.29 and Puntoriero et al.30), and inter-dendrimer energy transfer takes place with a time constant of about 18 ps (see main text). Chem 2017 3, 494-508DOI: (10.1016/j.chempr.2017.06.002) Copyright © 2017 Elsevier Inc. Terms and Conditions