Excited-state switching by per-flurination of para-oligophenylenes

Fluorination has become a versatile route to tune the electronic and optical properties of organic conjugated materials. Herein we report a new phenomenon, excited-state switching by per-fluorination of para-oligophenylenes, placing a low intensity 11B2 state below the 11B1 state, giving rise to large Stokes shifts. The switching is attributed to the specific impact of fluorine on the delocalized and localized frontier orbitals as elucidated by quantum-chemical calculations. The sterical demands of the fluorine atom additionally diminish efficient conjugation along the chain, leading to hypsochromic shifts with respect to the unsubstituted counterparts and to a weak chain length dependence of the absorption and unstructured emission spectra and enhanced internal conversion

Energy transfer at the zeolite l boundaries: Towards photo- and electroresponsive materials

A series of iridium(III) compounds have been used as stopper molecules at the pore openings of zeolite L and act as effective donor units for transferring excitation energy to dye molecules entrapped within the zeolite channels. The synthesis and photophysical characterization of the new iridium(III) complexes are described, along with F\ue7rster resonance energy-transfer experiments. Transfer efficiencies for the studied systems are discussed on the basis of the role played by the localization of the donor excited state and the acceptor distribution in the channels. Because iridium(III) complexes can also be electrically excited, the electroluminescent behavior of donor-acceptor zeolite systems can be explored, by embedding them into a polymeric active layer and constructing light-emitting devices (LEDs). Novel hybrid LEDs can be fabricated with emission from the dyes entrapped into the zeolites and sensitized by the electro-responsive iridium(III) complex

Fluoro-functionalization of vinylene units in a polyarylenevinylene for polymer solar cells

A low band-gap copolymer PDTBTFV alternating bis-thienyl-(bis-alkoxy)-benzothiadiazole blocks with difluorovinylene units and its non-fluorinated counterpart PDTBTV have been synthesized and characterized as donor materials in bulk heterojunction (BHJ) solar cells with PCBM as the acceptor. The solar cells with the fluorinated polymer show better photovoltaic performances than those recorded with the non-fluorinated material. Comparative spectroscopic and computational studies, together with morphological, electrical and optical characterization of thin films, have been carried out to shed light on the reasons for the improvement of performances as induced by the double bond fluorination. Our study introduces the fluorinated double bond as a new conjugated unit in donor polymers for BHJ solar cells