Porphyrin-based Self-assemblies For Use In Supramolecular Solar Cells

In nature, chlorophyll containing porphyrin macrocycle can be used to collect solarenergy and validly convert it into chemical energy. So, more and more researchershave been attempting to mimic such feature to construct artificial light-harvestingdevices. In this dissertaton, we design and organize a series of self-assemblies basedon zinc porphyrin derivatives, wherein zinc porphyrin derivatives appendedisonicotinic acid ligands by metal-ligand axial coordination and metal-ligand edgedbinding approaches are used to functionalize the nanostructured TiO2electrodesurfaces. In order to understand how molecules can be well-arranged on the electrodesurfaces, the different zinc porphyrin derivatives, metal ions, organic acid ligands andcoordination approaches are also designed and studied. The results are as follows:1. A series of N-heterocyclic-substituted zinc porphyrins and their correspondingcoordination polymers (CPs) have been successfully synthesized and immobilized onthe nanostructured TiO2electrode surfaces by zinc porphyrin derivatives combinedisonicotinic acid ligands by metal-ligand axial coordination and metal-ligand edgedbinding approaches. The SEM, AFM and computational simulation analyses have alsodemonsteated the assembled structures on electrode surfaces. Photoelectrochemicalstudies reveal that (1) the assembly based on iminazole-substituted zinc porphyrinexhibit significantly improved photovoltaic performance compared with theassemblies with pyridine/benzimidazole-substituted zinc porphyrins;(2) theperformances of the assemblies formed by metal-ligand axial coordination outperformthose of the assemblies constructed by metal-ligand edged binding approach;(3)CPs-isonicotinic acid assemblies show significantly improved photocurrent behaviors,especially for CPs of iminazole-substituted zinc porphyrin. These results are alsoverified by their respective UV-Vis absorption, fluorescence spectra, molecular orbital(MO) patterns and HOMO-LUMO energy gaps.2. To further probe the significantly enhanced photovoltaic performance of theCPs-based assembly, a series of acetohydrazide zinc porphyrins and their corresponding CPs have been successfully synthesized. Then, the assemblies withthese zinc porphyrin derivatives appended isonicotinic acid ligands by metal-ligandaxial coordination approach are immobilized on the nanostructured TiO2electrodesurfaces and perform the performances of the assemblies-sensitized solar cells. Theassembled structures are characterized by SEM, AFM and computational simulationanalyses. Compared to the assembly of zinc porphyrin, CP-isonicotinic acid assemblyshows a significantly enhanced photoelectronic behavior. In addition, In addition, aseries of different organic acid ligands are prepared to understand the impact of theirstructures on the photoelectronic performances of their respectiveassemblies-sensitized cells. Photo-electrochemical studies show that the assemblybased on the anchoring group bearing a shorter arm and mono-carboxylic acid unitexhibits a better photovoltaic performance. These products are also reflected by theirrespective UV-vis absorption, fluorescence spectra, molecular orbital (MO) patternsand HOMO-LUMO energy gaps.3. To assist the effect of different metal ions and anchoring groups in theassemblies-sensitized solar cells, a series of assemblies with acetohydrazide zincporphyrin constructed by the different metal ions to bind the zinc porphyrin anddifferent organic acid ligands are prepared, in which organic acid ligands serve asanchoring group to functionalize the TiO2electrode surfaces. The SEM, EDAX andcomputational simulation analyses are used to characterized the assembled structuresof these assemblies. Our results show that the assemblies based on anchoring groupbearing longer arm and pyridine-monocarboxylic acid unit appended theMn/Cd-mediums generate obviously improvement in solar-to-electrical conversationefficiency. These conclusions are also reflected by their respective UV-vis absorption,fluorescence spectra, molecular orbital (MO) patterns and HOMO-LUMO energygaps.