Electronic Energy Transfer to the S2 Level of the Acceptor in Functionalised Boron Dipyrromethene Dyes

Taking the high road: Highly efficient electronic energy transfer takes place from a set of appended aryl polycyclic hydrocarbons to an expanded boron dipyrromethene (Bodipy)-based dye (see figure) despite negligible spectral overlap with the lowest-energy excited state localised on the acceptor.A multi-component array has been constructed around an expanded boron dipyrromethene (Bodipy) dye that absorbs and emits in the far-red region. One of the appendages is a perylene-based moiety that is connected to the boron atom of the terminal Bodipy by a 1,4-diethynylphenylene connector. Despite the fact that there is almost negligible spectral overlap between fluorescence from the perylene unit and absorption by the Bodipy residue, electronic energy transfer is rapid and essentially quantitative. It is concluded that at least half of the photons absorbed by perylene are transferred to the upper-lying singlet excited state (S2) associated with the Bodipy-based acceptor. The second appendage is a pyrene unit that is covalently linked to fluorene, through an ethynylene spacer, and to the boron atom of the Bodipy terminus, through a 1,4-diethynylphenylene connector. Pyrene absorbs and emits at higher energy than perylene and there is strong spectral overlap with the Bodipy-based S2 state, and none with the corresponding S1 state. Electronic energy transfer is now very fast and exclusively to the S2 state of the acceptor. It is difficult to compute reasonable estimates for the rates of Coulombic energy transfer, because of uncertainties in the orientation factor, but the principle mechanism is believed to arise from electron exchange. Comparison with an earlier array built around a conventional Bodipy dye indicates that there are comparable electronic coupling matrix elements for the two systems. It is notable that pyrene is more strongly coupled to the Bodipy unit than perylene in both arrays. These new arrays function as highly effective solar concentrators

BODIPY derivatives as donor materials for bulk heterojunction solar cells

BODIPY derivatives have been used as donor in solution-processed bulk heterojunction solar cells using PCBM as acceptor. A power conversion efficiency of 1.34% has been obtained under simulated solar irradiation

A tailored hybrid BODIPY–oligothiophene donor for molecular bulk heterojunction solar cells with improved performances

Fixation of a 5-hexyl-2,2′-bithienyl unit on a conjugated BODIPY donor increases the conversion efficiency of the resulting molecular bulk heterojunction solar cells from 1.30 to 2.20%

Spectroscopic and Redox Properties of Novel d-Complexes Engineered from All Z-Ethenylthiophene-bipyridine Ligands

A series of quasilinear dinuclear complexes incorporating ruthenium(II)- and osmium(II)-tris(2,2′-bipyridine) units has been prepared in which the individual metal-containing moieties are separated by 3,4-dibutyl-2,5- diethenylthiophene spacers and end-capped by 3,4-dibutyl-2-ethenylthiophene subunits; related ruthenium(II) and osmium(II) mononuclear complexes have also been prepared where one bpy unit is likewise end-capped by 3,4- dibutyl-2-ethenylthiophene subunits [bpy ) 2,2′-bipyridine]. Overall, mononuclear species, labeled here Ru and Os, and dinuclear species, RuRu, OsOs, and RuOs, have been prepared and investigated. Their electrochemical behavior has been studied in CH3CN solvent and reveals ethenylthiophene-centered oxidations (irreversible steps at > +1.37 V vs SCE), metal-centered oxidations (reversible steps at +1.30 V vs SCE for Ru(II/III) and +0.82 V vs SCE for Os(II/III)), and successive reduction steps localized at the substituted bpy subunits. The spectroscopic studies performed for the complexes in CH3CN solvent provided optical absorption spectra associated with transitions of ligand-centered nature (LC, from the bpy and ethenylthiophene subunits) and metal-to-ligand charge-transfer nature (MLCT), with the former dominating in the visible region (400−600 nm). While the constituent ethenylthiophene- bpy ligands are strong fluorophores (fluorescence efficiency in CH2Cl2 solvent, φem ) 0.49 and 0.39, for the monomer and the dimer, respectively), only weak luminescence is observed for each complex in acetonitrile at room temperature. In particular, (i) the complexes Ru and RuRu do not emit appreciably, and (ii) the complexes Os, OsOs, and RuOs exhibit triplet emission of 3Os f L CT character, with φem in the range from 10-3 to 10-4. These features are rationalized on the basis of the role of nonemissive triplet energy levels, 3Th, centered on the ethenylthiophene spacer. These levels appear to lie lower in energy than the 3Ru f L CT triplet levels, and in turn higher in energy than the 3Os f L CT triplet levels, along the sequence 3Ru f L CT > 3Th > 3Os f L CT

Semi-conducteurs Isotropes et Stables pour Cellules solaires Organiques

Date du colloque : 03/2011</p

Chemistry at Boron: Synthesis and Properties of Red to Near-IR Fluorescent Dyes Based on Boron-Substituted Diisoindolomethene Frameworks

A general method for the synthesis of difluorobora-diisoindolomethene dyes with phenyl, p-anisole, or ethyl-thiophene substituents has been developed. The nature of the substituents allows modulation of the fluorescence from 650 to 780 nm. Replacement of the fluoro ligands by ethynyl-aryl or ethyl residues is facile using Grignard reagents. Several X-ray molecular structures have been determined, allowing establishment of structure–fluorescence relationships. When the steric crowding around the boron center is severe, the aromatic substituents α to the diisoindolomethene nitrogens are twisted out of coplanarity, and hypsochromic shifts are observed in the absorption and emission spectra. This shift reached 91 nm with ethyl substituents compared to fluoro groups. When ethynyl linkers are used, the core remains flat, and a bathochromic shift is observed. All the fluorophores exhibit relatively high quantum yields for emitters in the 650–800 nm region. When perylene or pyrene residues are connected to the dyes, almost quantitative energy transfer from them to the dye core occurs, providing large virtual Stokes shifts spanning from 8000 to 13 000 cm–1 depending on the nature of the dye. All the dyes are redox active, providing the Bodipy radical cation and anion in a reversible manner. Stepwise reduction or oxidation to the dication and dianion is feasible at higher potentials. We contend that the present work paves the way for the development of a new generation of stable, functionalized luminophores for bioanalytical applications

Organic Bulk-heterojunction Solar Cells Based on BODIPY Derivatives as Donors

Date du colloque&nbsp;: 10/2009</p

Bodipy derivatives for multi-donor bulk heterojunction solar cells

Date du colloque&nbsp;: 06/2010</p

Multi-donor molecular bulk heterojunction solar cells: improving conversion efficiency by synergistic dye combinations

Molecular bulk heterojunction solar cells with a power conversion efficiency of 1.70% have been fabricated using as donor BODIPY dyes with complementary light-harvesting properties

Multi-donor molecular bulk heterojunction solar cells based on BODIPY derivatives

Date du colloque&nbsp;: 07/2009</p