## 3 Results
### Electrochemical Properties  
Table 1 includes a summary of the cyclic voltammetry (CV) data collected in DCM (100 mV/s; 0.1 M NBu4 PF6; 2 mM aldehyde concentration; calibrated vs. normal hydrogen electrode (NHE) using octamethylferrocene as an internal standard). As previously  
Figure 2: Optical behavior of dyes **2a**, **2c**, and **2e** in DCM: (**a**) experimental UV-Vis absorption data for dyes **2a** (black), **2c** (red) and **2e** (green). TDDFT calculated dominant transitions (dashed lines) leading to the observed absorptions for **2a** are shown; (**b**) frontier molecular orbitals for **2a**, **2c**, and **2e** (left to right). Oscillator strengths provided for each dominant transition calculated from TDDFT. suggested, reversible electrochemistry was not observed in the dye family (**2b-e**). This has been attributed to a lack of solubility of the dye during oxidation and subsequent electrodeposition. Changing the supporting electrolytes or solvents yielded no improvement, and therefore the CV measurements were done using the aldehyde precursors (**3a-e**). As mentioned previously, TPA donors show good electrochemical reversibility and the addition of ferrocene provides a rich electrochemical cyclic voltammogram with three reversible oxidation waves; electrochemical reversible reductions were not observed (Figure 3). Consistent with our previous findings, all the dye precursors in Family 2 (**3a-e**) exhibit two well-resolved electrochemical reversible oxidations at higher potentials, owing to the presence of two electronically unique redox-active TPA units [54]. While it is certainly an over-simplification, the oxidation wave at lower potential is assigned to the more electron rich distal (relative to titania) TPA and the second oxidation is centered on the electron deficient proximal TPA unit with the aldehydes attached. The low potential wave (for **3b-3e**) is assigned to the ferrocene subunits added to the dye. Figure 3a visually highlights the oxidation behavior for the directly bound, mono- and bis-functionalized Fc-derivatives **3b** and **3c**, respectively. Relative to **3a**, the only significant change is the presence of ferrocene-containing groups and their oxidation at lower potentials. There is also a decrease in the resolution between the two TPA oxidation waves owing to the increase in the oxidation potential of the distal TPA unit. As ferrocene itself oxidizes at the lowest potential, the directly attached ferrocene unit(s) would serve as an electron-withdrawing ferrocenium cation post-oxidation, thus pushing the second oxidation (TPA-centered) wave to a higher potential. A similar result is observed for ferrocene-alkyne derivatives in Figure 3b. Another feature that both Figures 3a and 3b highlight is the effect of double-ferrocene substitution versus mono-substitution. Comparing the ferrocene oxidation waves **3b** to **3c** (and **3d** to **3e**, respectively), one can see a doubling of the ferrocene (Fc)/ferrocenium (Fc\({}^{+}\)) wave intensity upon double substitution. This suggests that both Fc/Fc\({}^{+}\) oxidations happen simultaneously at the same potential. This also suggests that the two oxidations happen independently and there is minimal electronic communication between the ferrocenes through the \(\pi\)-system of the TPA. There are also some noticeable differences between Figures 3a and 3b. The Fc/Fc+ oxidation wave potential of ferrocene alkyne derivatives **3d** and **3e** is approximately 100 mV higher than **3b** and **3c,** respectively. This is likely due to the inductive electron withdrawing effect of the alkyne, as previously discussed. One other notable feature is the pseudo-reversibility of **3c** during the third oxidation wave.