## 4 Discussion and Conclusions  
The original goal of this work was to investigate a new family of ferrocene-containing DSSC dyes based on our previously reported D-\(\pi\)-D-A dye architecture. Despite previous reports by [PERSON] et al. [50; 51], where they observed poor performance in devices using ferrocene-modified dyes (e.g., **1c**), we hypothesized that our dyes would mitigate these deleterious effects on back-electron transfer owing to their bis-TPA dye architecture and extended charge separation. [PERSON] et al. attributed poor performance to a quenched twisted intramolecular charge-transfer (TICT) behavior (vide supra), however we surmised that an extended \(\pi\)-system in our bis-TPA architecture could overcome this. To this end, we prepared directly bound ferrocene (**2b**, **2c**) and the alkyne ferrocene derivatives (**2d**, **2e**). Based on TDDFT calculations the optical behavior of both the directly-bound and alkyne-connected Fc derivatives looked promising (pre-synthesis) with panchromatic absorption envelopes; however, that was not realized experimentally. The directly bound ferrocene derivatives **2b** and **2c** have a similar absorption profile as **2a**, whilst the ferrocene alkyne derivatives (**2d** and **2e**) have a less desirable, blue-shifted spectrum. Future work will examine other basis sets in the TDDFT calculations to try and make better predictions for these hybrid dye systems. The electrochemical behavior for **2a-2e** seemed consistent based on the structural modifications. The alkyne ferrocene derivatives (**2d** and **2e**) have a slightly more positive Fc/Fc+ oxidation potential versus NHE, owing to the electron withdrawing nature of the alkyne bridge. This is pleasing because it suggests a degree of tunability of the ferrocene oxidation potential through chemical modification. Generally, there appeared to be a lack of electronic communication within the dye that manifested in the redox active components behaving independently, with notable exceptions being a minor shift in the distal TPA oxidation. This was more likely due to the electrostatic electron withdrawing effect of the oxidized ferrocenium cation rather than communication between the electrophores. Device performance of all ferrocene-containing dyes presented herein was dismal, and drastically underperformed relative to the non-ferrocene containing benchmarks **1a** and **2a**. Despite the success of using iron-based electrolytes [60; 61; 62] and other ferrocene-modified dyes motifs [33; 34], our poor device performance is consistent with rapid TiO\({}_{2}\)-Fc\({}^{+}\) recombination observed for other TPA-based dyes containing ferrocene [50; 51]. However, examining the stability of the ferrocene in a model electrolyte environment using spectro-electrochemical measurements seems to suggest that the stability of ferrocene-modified organic dyes is also a potential problem. In our case, without rigorous attempts to avoid oxygen during device preparation, one possible decomposition pathway could be degradation of the ferrocenium by molecular oxygen or electrolyte additives, as discussed previously [63]. Finally, perhaps the ultimate limitation of using ferrocene dyes involves our choice of electrolyte. As elaborated in Figure 5, the regeneration of oxidized dye with iodide leads to the formation of the diiodide radical (I\({}_{2}\)\({}^{-\bullet}\)), and the redox potential of this couple must also be considered when determining the driving force for dye regeneration [64]. As such, it is possible that ferrocene is being oxidized by the I\({}_{2}\)\({}^{-\bullet}\) species and converting into ferrocenium either in ambient conditions or when the dye is in the excited state [65]. Regardless, when considering this family of ferrocene-containing dyes, the lack of sufficient driving force for regeneration also impedes device performance. As such, perhaps usingother electrolytes or tuning the redox potential of the ferrocene could be explored to overcome this deleterious behavior.