Energy migration in dendritic oligothiophene-perylene bisimides.

A series of novel oligothiophene-perylene bisimide hybrid (DOTPBI) dendrimers up to the second generation (G0, G1, and G2) were investigated. Optical measurements such as nonlinear optical and time-resolved spectroscopy, including two-photon absorption, fluorescence upconversion, and excited state transient absorption were carried out. Results of these measurements revealed the ability of these molecules to undergo intramolecular fluorescence resonance energy transfer (FRET) from the dendritic oligothiophenes (DOT) to the perylene bismide (PBI) moiety. The delocalization length and the photoinduced electron transfer (PET) rate were investigated as a function of dendrimer generation. A fast energy transfer process from the DOT dendron to the PBI core was observed. For the case of the G2 dendrimer, with relatively large thiophene dendrons attached to the bay area of the perylene bisimide, the PBI core is highly twisted and its ability to self-assemble into π-π stacked aggregates is destroyed. As a result, among the three generations studied, G1, which has the best two-photon cross section and the most efficient energy transfer, is the best light harvesting material.

Preparation of functionalized cyclic enol phosphates by halogen-magnesium exchange and directed deprotonation reactions.

Cyclic enol phosphates were magnesiated by a halogen/magnesium exchange reaction or deprotonation using TMP-derived magnesium amide bases. The resulting magnesium reagents react readily with a wide range of electrophiles like allyl bromides and acid chlorides or can be used in Pd-catalyzed cross-coupling reactions. Several optically pure enol phosphates were prepared starting from readily available d-(+)-camphor derivatives.

Design and synthesis of a novel anchoring ligand for highly efficient thin film dye-sensitized solar cells.

A novel ligand, 5,5'-(2,2'-bipyridine-4,4'-diyl)-bis(thiophene-2-carboxylic acid) (BTC), and its Ru(II) complex (BTC-1) in which the anchoring group is attached to the thiophene units were developed. Using a low-volatility electrolyte and 3.3 mum mesoporous TiO2 films BTC-1 achieved a solar-to-electricity conversion efficiency of 6.1%, compared to 4.8% for N719 under the same experimental conditions.

A dendritic oligothiophene ruthenium sensitizer for stable dye-sensitized solar cells.

We report a new type of dendritic terthiophene attached to a 2,2'-bipyridine ligand for ruthenium-based dye-sensitized solar cells. As a result of the incorporation of this electron-rich terthiophene donor unit into the heteroleptic ruthenium sensitizer [Ru(dcbpy)(3Tbpy)(NCS)(2)] (3T), the lowest-energy metal-to-ligand charge transfer (MLCT) transition is red-shifted and the molar extinction coefficient is increased compared to the analogous standard Z907Na sensitizer. A preliminary investigation of the 3T dye in combination with an iodine/iodide-based electrolyte shows an interesting photovoltaic performance, with a maximum power conversion efficiency of 7.4 % measured under air mass 1.5 global sunlight irradiation. Accelerated testing of these devices at 60 degrees C under full sunlight soaking shows a remarkable stability over 1000 h.

Functionalized dendritic oligothiophenes: ruthenium phthalocyanine complexes and their application in bulk heterojunction solar cells.

Within the present work, two series of novel ruthenium(II) phthalocyanine (RuPc) complexes with one [RuPcCOPy-nT] or two [RuPc(Py-nT)(2)] dendritic oligothiophene (DOT) ligands in the axial positions are reported. The ability of Ru(II) for axial coordination in RuPcs allowed the attachment of the Pc through the metal site to the DOT-ligands bearing pyridine at the core position of the dendrons. These extended pyridine functionalized conjugated DOT-ligands (Py-nT) were chosen to cover the spectral window between 380 and 550 nm, where the RuPc does not exhibit a strong absorption, in order to improve the light-absorption of these complexes and hence enhance the efficiency of the corresponding solar cells. Good efficiencies of up to 1.6% have been achieved when blended together with a fullerene acceptor in solution-processed photovoltaic devices, providing by far the best phthalocyanine-based bulk heterojunction solar cells reported to-date.

Metal-free organic dyes for dye-sensitized solar cells: from structure: property relationships to design rules.

Dye-sensitized solar cells (DSSC) have attracted considerable attention in recent years as they offer the possibility of low-cost conversion of photovoltaic energy. This Review focuses on recent advances in molecular design and technological aspects of metal-free organic dyes for applications in dye-sensitized solar cells. Special attention has been paid to the design principles of these dyes and on the effect of various electrolyte systems. Cosensitization, an emerging technique to extend the absorption range, is also discussed as a way to improve the performance of the device. In addition, we report on inverted dyes for photocathodes, which constitutes a relatively new approach for the production of tandem cells. Special consideration has been paid to the correlation between the molecular structure and physical properties to their performance in DSSCs.