Christina Stangel

A supramolecular assembling of zinc porphyrin with a π-conjugated oligo(phenylenevinylene) (oPPV) molecular wire for dye sensitized solar cell

A novel π-conjugated oligo(phenylenevinylene) (oPPV) (or LC) was prepared, as a new organic dye for dye-sensitized solar cells (DSSC), which contains a cyanoacrylic acid group on one end and a pyridyl group on the other. Solar cells sensitized by LC were fabricated, and were found to exhibit a power conversion efficiency (PCE) value of 2.45%. Furthermore, we describe the formation of a supramolecular dyad (ZnTPP–LC) via a metal–ligand bond between LC, since its pyridyl group allows it to interact with several metal centers, and zinc-tetraphenyl-porphyrin (ZnTPP) onto the photoelectrodes TiO2 surface of the solar cell. More specifically, LC was bound at first onto TiO2 with its cyanoacrylic acid anchoring group, and then a metal–ligand supramolecular bond was formed, with the addition of a porphyrinic solution, between the nitrogen atom of LCs pyridyl group and the zinc. ZnTPP–LC solar cell was then fabricated resulting in a record PCE value of 5.27% concerning the supramolecular DSSCs. As shown by photovoltaic measurements (J–V curves) and incident photon to current conversion efficiency (IPCE) spectra of the two solar cells, the higher PCE value of the supramolecular one can be attributed to its enhanced photovoltaic parameters, and particularly its enhanced short circuit current (Jsc). This Jsc improvement is due to ZnTPP–LCs higher light-harvesting efficiency and the larger electron injection of both ZnTPP and LC into TiO2s conduction band (CB) of the corresponding solar cell. These results are in accordance with electrochemical impedance spectra (EIS) of the DSSCs, which revealed longer electron lifetime, higher charge recombination resistance and shorter electron transport time for the solar cell based on ZnTPP–LC as compared to the one sensitized by LC.

Axially Assembled Photosynthetic Antenna-Reaction Center Mimics Composed of Boron Dipyrromethenes, Aluminum Porphyrin, and Fullerene Derivatives

Sequential photoinduced energy transfer followed by electron transfer leading to the formation of charge separated states in a newly assembled series of supramolecular triads comprised of boron dipyrromethenes (BODIPY or BDP), aluminum porphyrin (AlTPP) and C60 is demonstrated. In the present strategy, the energy donor (BDP) and electron acceptor (C60) were axially positioned to the plane of AlTPP via the central metal. The structural integrity of the newly synthesized compounds and self-assembled systems were fully established using spectral, electrochemical and computational methods. Thermodynamic feasibility of energy transfer from 1BDP* to AlTPP and subsequent electron transfer from 1AlTPP* to generate BDP-AlTPP•+-C60•- charge separated states was derived from free-energy calculations. Occurrence of ultrafast energy transfer from 1BDP* to AlTPP was established from studies involving steady-state and time-resolved emission, as well as femtosecond transient spectroscopic techniques. The BDP-AlTPP•+-C60•- charge separated states persisted for several nanoseconds prior returning to the ground state.

Electrostatic Association of Ammonium Functionalized Layered Transition Metal Dichalcogenides with an Anionic Porphyrin

Ammonium-modified MoS2 and WS2 were prepared and characterized by complementary spectroscopic, thermal, and microscopic means. The positive charges on functionalized MoS2 and WS2, due to the presence of ammonium units, were exploited to electrostatically bring in contact an anionic porphyrin bearing a carboxylate moiety, yielding porphyrin/MoS2 and porphyrin/WS2 ensembles, 5a and 5b, respectively. Efficient photoluminescence quenching of porphyrins emission by MoS2 and WS2 within nanoensembles 5a and 5b, in combination with time-resolved photoluminescence assays, revealed transduction of energy from the photoexcited porphyrin to MoS2 or WS2.