Maxence Urbani

Meso-substituted porphyrins for dye-sensitized solar cells.

Among the several approaches for harnessing solar energy and converting it into electricity, dye-sensitized solar cells (DSSC) represent one of the most promising methods for future large-scale power production from renewable energy sources. In these cells, the sensitizer is one of the key components harvesting solar radiation and converting it into electric current. The electrochemical, photophysical, and ground and excited state properties of the sensitizer play an important role for charge transfer dynamics at the semiconductor interface. Moreover, for long-term stability and practical applications, electrolytes based on the iodine/triiodine couple also suffer from two other disadvantages: the corrosive effect toward the metal electrodes, and the partial absorption of the visible light by triiodine anions. These issues hence constitute one of the reasons that have encouraged the development of alternative iodine-free redox couples in liquid electrolytes for DSSCs.

Porphyrin–Phthalocyanine/Pyridylfullerene Supramolecular Assemblies

The synthesis and photophysical properties of several porphyrin (P)-phthalocyanine (Pc) conjugates (P-Pc; 1-3) are described, in which the phthalocyanines are directly linked to the β-pyrrolic position of a meso-tetraphenylporphyrin. Photoinduced energy- and electron-transfer processes were studied through the preparation of H(2)P-ZnPc, ZnP-ZnPc, and PdP-ZnPc conjugates, and their assembly through metal coordination with two different pyridylfulleropyrrolidines (4 and 5). The resulting electron-donor-acceptor hybrids, which were formed by axial coordination of compounds 4 and 5 with the corresponding phthalocyanines, mimicked the fundamental processes of photosynthesis; that is, light harvesting, the transduction of excited-state energy, and unidirectional electron transfer. In particular, photophysical studies confirmed that intramolecular energy-transfer resulted from the S(2) excited state as well as from the S(1) excited state of the porphyrins to the energetically lower-lying phthalocyanines, followed by an intramolecular charge-transfer to yield P-Pc(.+)⋅C(60)(.-). This unique sequence of processes opens the way for solar-energy-conversion processes.

Supramolecular click chemistry for the self-assembly of a stable Zn(II)–porphyrin–C60 conjugate

Owing to the complementarity between a bis-Zn(II)-porphyrin receptor and a fullerene ligand bearing two pyridine substituents, the substrate can be clicked onto the ditopic receptor, thus leading to a stable non-covalent macrocyclic 1 ratio 1 complex.

Large photoactive supramolecular ensembles prepared from C60–pyridine substrates and multi-Zn(II)–porphyrin receptors

Fullerene derivatives bearing a pyridine sub-unit have been prepared. Their ability to form self-assembled supramolecular structures with mono- and polytopic Zn(II)–porphyrin receptors has been first evidenced by UV-vis studies. These supramolecular complexes are multi-component photoactive devices, in which the emission of the porphyrinic receptor is dramatically quenched by the fullerene units. This new property, resulting from the association of the different molecular sub-units, also allowed us to investigate in detail the self-assembly process using fluorescence titrations. The binding studies revealed positive cooperative effects for the assembly of the C60–pyridine derivatives with polytopic receptors as a result of intramolecular C60–C60 interactions between the different guests assembled onto the multi-Zn(II)–porphyrin hosts.

Adapting Ruthenium Sensitizers to Cobalt Electrolyte Systems

In this work, we report the use of bulky substitutions in a new heteroleptic ruthenium(II) bipyridine complex, Ru(NCS)2LL, coded TT-230 to obtain high open-circuit potential in a dye-sensitized solar cell (where L is a bipyridine ligand appended with two cyclopenta(2,1-b;3,4-bA)dithiophene moieties, and L = 4,4,-dicarboxylic acid 2,2-bipyridine). The electrolytes based on cobalt complexes have shown significant advantages in terms of attainable open-circuit potential compared to the standard iodide/tri-iodide redox mediators. These merits of the cobalt complexes were previously realized with a porphyrin sensitizer, achieving a VOC greater than 1 V in DSC. However, with conventional Ru(II)-polypyridyl complexes such as the C101 dye, similar increase in the VOC could not be attained due to the enhanced recombination. In this work, we have shown that the use of bulky substituents can prevent the back reaction of photogenerated electron and subsequently increase the open-circuit potential of the device. The recombination processes were investigated by transient photovoltage decay measurements.

Synthesis of Amphiphilic Ru-II Heteroleptic Complexes Based on Benzo[1,2-b:4,5-b]dithiophene: Relevance of the Half-Sandwich Complex Intermediate and Solvent Compatibility

The detailed synthesis and characterization of four ruthenium(II) complexes [RuLL(NCS)2 ] is reported, in which L represents a 2,2-bipyridine ligand functionalized at the 4,4 positions with benzo[1,2-b:4,5-b]dithiophene derivatives (BDT) and L is 2,2-bipyridine-4,4-dicarboxylic acid unit (dcbpy) (NCS=isothiocyanate). The reaction conditions were adapted and optimized for the preparation of these amphiphilic complexes with a strong lipophilic character. The photovoltaic performances of these complexes were tested in TiO2 dye-sensitized solar cell (DSSC) achieving efficiencies in the range of 3-4.5u2009% under simulated one sun illumination (AM1.5G).

Effect of Peripheral Substitution on the Performance of Subphthalocyanines in DSSCs

A series of six new subphthalocyanines (SubPcs) bearing an ethynylcarboxyphenyl anchoring unit and decorated with a variety of substituents at the peripheral position of the macrocycle have been synthesized in order to investigate the effect of the peripheral substituent on the performance of dye-sensitized solar cells.

Photoinduced electron transfer in a meso-linked Zn(II)porphyrin-Zn(II)phthalocyanine/C60-pyridyl supramolecular system

A non-covalent supramolecular complex combining porphyrin (Por), phthalocyanine (Pc) and fullerene [C60], was obtained through zinc metal-pyridine coordination between a covalently meso-linked heterodimer ZnPor-ZnPc (4) and a N-pyridylfulleropyrrolidine derivative (5). The complexation was studied in toluene by absorption and fluorescence binding studies, and evidenced that the coordination of the N-pyridylfulleropyrrolidine (5) occurs preferentially through the zinc ion center of ZnPc (log K > 6.0) rather than ZnPor (log K = 5.23). Steady-state and time-resolved spectroscopies evidenced that upon selective excitation of either the Por, or the Pc moiety in [(ZnPor-ZnPc)∪C60], the singlet excited state of Pc was generated efficiently in both cases (either from singlet-singlet energy transfer from 1Por* to Pc, or directly after selective excitation of the Pc moiety). Next, an electron transfer occurred from the 1Pc* to the C60 to generate the charge-separated specie [(ZnPor-ZnPc•+)∪C60•-]. Finally, the back electron transfer afforded the Pc triplet excited state rather than the ground state. The introduction of a covalent meso-linkage between Por and Pc in the heterodimer 4 and in the supramolecular assembly 4∪5 induces appreciable differences toward the photo-induced processes and the binding constants in comparison with other β-covalently linked analogue systems.

A macrocyclic supramolecular complex obtained from a fullerene ligand bearing two pyridine substituents and a bis-Zn(II)-porphyrin receptor

A fullerene derivative bearing two pyridine subunits has been designed to allow assembly with a bis-Zn(II)-phorphyrin receptor with two equivalent Zn binding sites separated by about 20 A. Owing to the complementarity between the bis-Zn(II)-porphyrin receptor and a fullerene ligand bearing two pyridine substituents, the substrate can be clicked on the ditopic receptor, thus leading to a stable non-covalent macrocyclic 1:1 complex.

ABAB Phthalocyanines: Scaffolds for Building Unprecedented Donor–π–Acceptor Chromophores

Abstract Unique donor–π–acceptor phthalocyanines have been synthesized through the asymmetric functionalization of an ABAB phthalocyanine, crosswise functionalized with two iodine atoms through Pd‐catalyzed cross‐coupling reactions with adequate electron‐donor and electron‐acceptor moieties. These push–pull molecules have been optically and electrochemically characterized, and their ability to perform as chromophores for dye‐sensitized solar cells has been tested.