# Self-Assembled Multinuclear Complexes for Cobalt(II/III) Mediated Sensitized Solar Cells
## 3 Results and Discussion
### Spectroscopic Properties
#### 3.1.2 Multinuclear Systems  
The realization of self-assembly systems via Ag\({}^{+}\) bridges benefits from previous literature where (Bu\({}_{4}\)N)\({}_{2}\)Ru(DCBH)\({}_{2}\)(NCS)\({}_{2}\)[23] (DCBH\({}_{2}\) = 4,4\({}^{\prime}\) dicarboxy-2,2\({}^{\prime}\) bipyridine) and the complex Ru(bpy)\({}_{2}\)(CN)\({}_{2}\)[11] (bpy = 2,2\({}^{\prime}\) bipyridine) were able to interact with Ag\({}^{+}\) by using the non-bonding \(\sigma\) pairs of either nitrogen or sulfur atoms of CN and NCS ligands. In particular, in the case of CN groups, high CN-Ag\({}^{+}\) association constants have been reported, indicating the possibility of exploiting these building blocks to create multinuclear species of different stoichiometry. As a general electronic effect, the coordination by Ag\({}^{+}\) causes the stabilization of d(\(\pi\)) of the Ru(II), resulting in a hyposochromic shift of the MLCT transitions. When **Z907** or **1** (Ru(TMAM)) are mixed with Ag\({}^{+}\) in a proper stoichiometric ratio (2 2907:1 Ag\({}^{+}\) (**3**) and **1** Ru(TMAM): 1 Ag\({}^{+}\) (**2**)), one observes a blue shift of the visible bands of the order of ca. 25-30 nm, associated with a ca. 20% decrease in the extinction coefficient of the charge transfer bands (Table 1 and Figure 3). This is suggestive of a decreased transition dipole consistent with the electron withdrawing effects of Ag\({}^{+}\), which decreases the electron density of both Ru(II) and ancillary ligands. IR spectroscopy provides further proof of Ag\({}^{+}\) coordination since, upon coordination of the latter, the stretching bands of both NCS and CN split, with the appearance of a band peaking at a frequency of 30/40 cm\({}^{-1}\) higher than that of the uncoordinated groups (Figure S12). This band originates from the kinematic coupling and is typical of bridging ligands (i.e., Ag-NC-Ru and Ag-SCN-Ru groups) where the motion of either NCS or CN groups is constrained by the presence of a second metal center [24,25]. \begin{table}
\begin{tabular}{c c c c c c c} \hline  & & **Absorption** & & **Emission** & & **E00/eV** \\ \cline{2-6}  & \(\lambda_{\text{max}}/\text{nm}\) & \(\varepsilon/\text{M}^{-1}\text{cm}^{-1}\) & \(\lambda/\text{nm}\) & \(\lambda_{\text{max}}/\text{nm}\) & \(\tau\) */ns & \\  & **MLCT** & **MLCT** & \(\pi\)-\(\pi\) * & \(\lambda_{\text{max}}/\text{nm}\) & \(\tau\) */ns & \\ \hline
**Z907** & 540, 417 & 12,047, 12,935 & 315, 295 \({}^{\text{Sh}}\) & \(>\)850 & \(<\)10 & 1.71 \\ \hline
**1** & & & & & & \\ (Ru(TMAM)) & 490, 358 & 10,858, 9487 & 301 & 700 & 189 & 2.13 \\ \hline
**2** & & & & & & \\ (Ru(TMAM)-Ag\({}^{+}\)) & 467, 343 & 9520, 9498 & 299 & 665 & 222 & 2.18 \\ \hline
**3** & & & & & & \\ (2Z907-Ag\({}^{+}\)) & 514, 406 & 9011, 9384 & 314, 295 \({}^{\text{Sh}}\) & 790 & 23 & 2.03 \\ \hline
**4** & & & & & & \\ (Z2907-Ag\({}^{+}\)-Ru(TMAM) & 503, 442 \({}^{\text{Sh}}\), 361 & 13,570, 12,944 & 314 \({}^{\text{Sh}}\), 300 & 744 & / & / \\ \hline \end{tabular} Sh = shoulder, * = methanol.  
\end{table} 
Table 1: Spectroscopic futures of the different systems in ethanol. Figure 2: (**a**) Comparison between the normalized absorption spectra of **1** [Ru(TMAM)\({}_{2}\)CN\({}_{2}\)]\({}^{4+}\) (green line) and of the precursor [Ru(TMAM)\({}_{2}\)Cl\({}_{2}\)]\({}^{4+}\) (violet line) values in ethanol. (**b**) Cyclic voltammetry of **1** (Ru(TMAM)) in 0.1M LiClO\({}_{4}\)/ACN at 50 mV/s at a glassy carbon electrode. Voltage is referred to SCE. **4** (2Z907-Ag+-(Ru(TMAM)) exhibits UV-Vis spectral features that are the exact sum of the individual complexes **3** and **2** (Figure 3 and Figure S13). This results in a wide visible absorption in the visible region, up to 700 nm, with an average extinction coefficient of ca. 1.4 \(\times\) 10\({}^{4}\) M\({}^{-1}\) cm\({}^{-1}\) between 500 and 350 nm.