## 4 Conclusions  
Quinoxaline was successfully employed and studied as a \(\pi\)-bridge for four dyes using the dual donor, dual acceptor (DD-\(\pi\)-AA) construct. The effect of structural modifications was studied via UV-Vis absorption spectroscopy, electrochemical analysis, computational DFT analysis, TCSPC spectroscopy, and DSC device analysis. With this design, dyes could be rationally designed, which absorb light beyond 750 nm in solution. The evaluation of the dye energetics on film showed that the dye anchor spacing plays a critical role in the validity of using solution measurements to approximate dye-TiO\({}_{2}\) film energetics. The anchor group spacing using two benzoic acid groups _ortho_ substituted on a 6-member ring provides a reliable group arrangement for rational dye energy level translation from solution to TiO\({}_{2}\) films. Additionally, the IPCE spectrum onset shifts dramatically in some cases further exacerbating the challenge of trying to reliably predict dye energetics within a working DSC device regardless of if the estimates for dye energetics were made on film or in solution. **AP12** has the widest IPCE response reaching beyond 800 nm. This is an exceptional IPCE onset for an organic dye and was presumably due in part to dye-electrolyte interaction as the dye-TiO\({}_{2}\) absorption onset was 80 nm blue-shifted compared with the IPCE onset. TCSPC studies revealed short excited-states for all of the dyes in this series, but with the addition of Li ions, dye-emission became unobservable, indicating that electron transfer from the dye to TiO\({}_{2}\) upon photoexcitation was facile. These results suggest that the primary drawback for this dye design is the poor molar absorptivities, such as 5,600 M\({}^{-1}\) cm\({}^{-1}\) for **AP12**. Future dye designs will focus on bolstering the dye molar absorptivities while retaining good electron transfer kinetics with properly spaced dual anchor groups.  
**Supplementary Materials:** The following are available online at [[http://www.mdpi.com/2076-3417/8/9/1421/s1](http://www.mdpi.com/2076-3417/8/9/1421/s1)]([http://www.mdpi.com/2076-3417/8/9/1421/s1](http://www.mdpi.com/2076-3417/8/9/1421/s1)). Synthetic Details for **AP9** and **AP12**; General Computational Information; General Photovoltaic Measurement Information; Device Fabrication Protocol; Time-Correlated Single Photon Counting General Information; Figure S1. Cyclic voltammetry plots of **AP** dyes in DCM solution and on TiO\({}_{2}\); Figure S2. \({}^{1}\)H NMR spectrum of compound **3** (CDCl\({}_{3}\), 500 MHz); Figure S3. \({}^{13}\)C NMR spectrum of compound **3** (CDCl\({}_{3}\), 75 MHz); Figure S4. \({}^{1}\)H NMR spectrum of compound **AP9** (DMSO-\(d\)6, 500 MHz); Figure S5. \({}^{1}\)H NMR spectrum of compound **6** (CDCl\({}_{3}\), 500 MHz); Figure S6. \({}^{13}\)C NMR spectrum of compound **6** (CDCl\({}_{3}\), 125 MHz); Figure S7. \({}^{1}\)H NMR spectrum of compound **7** (CDCl\({}_{3}\), 300 MHz); Figure S8. \({}^{1}\)H NMR spectrum of compound **9** (CDCl\({}_{3}\), 300 MHz); Figure S9. \({}^{13}\)C NMR spectrum of compound **9** (CDCl\({}_{3}\), 75 MHz); Figure S10. \({}^{1}\)H NMR spectrum of compound **AP12** (DMSO-\(d\)6, 500 MHz, 80\({}^{\rm o}\)C); and DFT cartesian coordinates for the **AP** series dyes.  
[PERSON] conceived and designed the experiments; [PERSON], [PERSON], [PERSON] and [PERSON] performed the experiments and analyzed data; [PERSON] and [PERSON] analyzed the data, contributed reagents/materials/analysis tools, and guided the experiments; [PERSON] and [PERSON] wrote the paper.  
[PERSON], [PERSON], [PERSON], and [PERSON] thank the National Science Foundation for its generous support through a CAREER Award NSF-1455167. [PERSON] and [PERSON] thank the National Science Foundation for Award OIA-1539035.  
The authors declare no conflicts of interest.