## 3 Result and Discussion
### Electrochemical Properties  
For dyes to function efficiently in DSC devices, the dye energy levels should be thermodynamically well positioned relative to the TiO\({}_{2}\) CB for efficient electron injection and the redox shuttle for efficient dye regeneration. Thus, electrochemical measurements were carried out in dichloromethane solutions and on TiO\({}_{2}\) electrodes to evaluate the suitability of these dyes to work in DSC devices based on TiO\({}_{2}\) and I\({}^{-}\)/I\({}_{3}\)\({}^{-}\). The ground-state oxidation potentials (\(E_{\text{(S+/S)}}\)) of the dye should be lower in energy than \begin{table}
\begin{tabular}{l c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Absorbance Data [a]**} & \multicolumn{4}{c}{**Electrochemical Data**} \\ \hline \multirow{3}{*}{**Dye**} & \(\lambda_{\text{max}}\) & \(\lambda_{\text{onset}}\)**DCM** & \(\lambda_{\text{onset}}\)**TiO\({}_{2}\)** & **IPCE\({}_{\text{onset}}\)** & \(\epsilon\) (M\({}^{-1}\) & \(E_{\text{(S+S)}}\)) & \(E_{\text{g}}\)**\({}^{\text{opt}}\)** & \(E_{\text{(S+/S)}}\) & \(E_{\text{(S+/S)}}\) & \(E_{\text{(S+/S)}}\) \\  & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(cm\({}^{-1}\))** & **DCM** & **(eV)**\({}^{\text{[bl]}}\) & **DCM**\({}^{\text{[bl]}}\) & **TiO\({}_{2}\) & **IPCE**\({}^{\text{[bl]}}\) \\ \hline
**AP6** & 479 & 560 & 585 & 590 & 12,000 & 0.88 & 2.21 & \(-\)1.33 & \(-\)1.24 & \(-\)1.22 \\
**AP8** & 531 & 640 & 570 & 675 & 8,000 & 0.90 & 1.94 & \(-\)1.04 & \(-\)1.28 & \(-\)0.94 \\
**AP9** & 590 & 770 & 660 & 680 & 5,500 & 0.88 & 1.61 & \(-\)0.73 & \(-\)1.00 & \(-\)0.94 \\
**AP12** & 588 & 720 & 720 & 800 & 5,600 & 0.89 & 1.72 & \(-\)0.83 & \(-\)0.83 & \(-\)0.66 \\ \hline \hline \end{tabular} \({}^{\text{[a]}}\) Onset values are taken as the x-intercept of a downward tangent line on the absorption curves on the low-energy side; \({}^{\text{[bl]}}\) Calculated from the equation \(E_{\text{g}}\)\({}^{\text{opt}}=1240/\lambda_{\text{onset}}\); \({}^{\text{[c]}}\) Calculated from the equation \(E_{\text{(S+/S)}}\)\({}^{\text{opt}}=E_{\text{(S+/S)}}\)\({}^{-}E_{\text{g}}\)\({}^{\text{opt}}\).  
\end{table} 
Table 1: Optical and electrochemical data of **AP6**, **AP8**, **AP9**, and **AP12**. Figure 2: (**a**) Molar absorptivities of **AP6**, **AP8**, **AP9**, and **AP12** in DCM and (**b**) normalized absorption on TiO\({}_{2}\). the redox shuttle (0.35 V vs. normal hydrogen electrode (NHE)). All of the dyes had similar \(E_{\text{(S+/S)}}\) values within 20 mV ranging from 0.88 to 0.90 V both in DCM and on TiO\({}_{2}\) (Table 1, Figure 3 and Figure S1). Thus, all the dyes can undergo thermodynamically favorable electron transfers from I\({}^{-}\) to regenerate the neutral dye after electron injection into TiO\({}_{2}\). This suggests that despite the dye conformation change when the solution and film absorption spectrum were compared, no significant effect was seen for any of the dyes via the \(E_{\text{(S+/S)}}\) value measurements. Therefore, all of the energetic changes with regard to the narrowing or widening of the optical energy gap on film relative to solution is due to changes in the excited-state oxidation potentials (\(E_{\text{(S+/S)}}\)). This observation is somewhat intuitive, because the \(E_{\text{(S+/S)}}\) values are primarily controlled by the dye acceptor groups anchored to the TiO\({}_{2}\) surface. The \(E_{\text{(S+/S)}}\) values were estimated via the equation \(E_{\text{(S+/S)}}=E_{\text{(S+/S)}}-E_{\text{g}}^{\text{opt}}\) for the **AP** dyes both on TiO\({}_{2}\) and in solution. Because the dye structural modifications had little effect on the \(E_{\text{(S+/S)}}\) values, and the dye \(E_{\text{g}}^{\text{opt}}\) values were found to vary broadly via UV-Vis spectroscopy in solution, a broad range of \(E_{\text{(S+/S)}}\) values are observed for this series ranging from \(-\)0.73 to \(-\)1.33 V vs. NHE. All of these values indicate a thermodynamically favorable electron transfer to the TiO\({}_{2}\) CB from a photoexcited dye.