本研究使用電子密度泛函理論 (Density Functional Theory, DFT) 計算一系列新型太陽能染料分子。我們探討染料分子在質子化、去質子化，以及吸附於 (TiO2)10 cluster 三種不同狀態下的基態結構、分子軌域 (frontier molecular orbitals)、能階與吸收光譜。在結構分析的部分，分析triphenylamine, fluorene, thiophene, benzene 及 EDOT 等芳香環，其兩兩之間的共軛性；結果顯示，thiophene 及 EDOT 具有比 benzene 更好的共軛性。 另外，本研究也利用 time-dependent density functional theory (TD-DFT) 模擬出與實驗相當吻合的吸收光譜，判斷此系列有機染料分子是以質子化的狀態存在於溶劑中。當染料吸附至 (TiO2)10 cluster 時，無論是計算或實驗(吸附於 TiO2 薄膜)得到的吸收光譜，其吸收位置都比在 THF 溶劑下藍位移(> 30 nm)；造成此一現象的原因，由結構分析推測，可能是由於 carboxylic groups 接到 (TiO2)10 cluster 時， carboxylic groups 與鄰近分子結構的共軛性變差。此研究也分析染料分子在照光激發前後的電子密度分佈在各個芳香環及 anchor 的變化，結果顯示分子受光激發後，電子的確由 donor 端向 acceptor/anchor 端傳遞，因而推測此系列染料分子有潛力能夠應用於染料敏化太陽能電池。 The ground state molecular structure, frontier molecular orbitals, energy levels, intramolecular charge transfer and absorption spectra of several newly synthesized solar-cell dye sensitizers are studied using density functional theory. The properties of these dye sensitizers are investigated under three different molecular states, protonated, deprotonated and adsorbed on (TiO2)10 cluster. Geometrical analysis summarizes the degree of conjugation of two aromatic rings such as triphenylamine, fluorene, thiophene, benzene and EDOT. Results show the thiophene and EDOT are more effective ?-conjugated spacers than benzene ring. Time-dependent density functional theory calculations show the simulated absorption spectra are excellent agreement with experimental spectra when the dye sensitizers are at their protonated states in solution. Upon adsorbing on TiO2 cluster, calculations as well as experiments show the absorption spectra are blue-shifted in relative to those in THF solution. These results are arisen from the de-conjugation of carboxylic groups when they are attached to (TiO2)10 cluster derived from geometrical analysis. The electron density difference analysis show the photoexcitation transfers the electron density on the electron-donating moiety to the acceptor/anchoring side allowing these dyes to be effective and potential in the dye-sensitized solar cell applications.
