Contrôle cationique des propriétés d'émission de luminescence au sein de dyades Pyrène-2, 2'-Bipyridine. Conception, synthèse, études spectroscopiques et théoriques

Au cours de ce travail nous avons conçu et synthétisé une nouvelle famille d'oligomères conjugués photoactifs incorporant le chromophore pyrène et l'unité chélatante 2,2'-bipyridine. Ces deux groupes sont assemblés de façon covalente aux extrémités d'un pont de type oligo(phénylène vinylène) ou oligo(phénylène éthynylène). L'étude photophysique de ces ligands montre combien la complexation d'un ion métallique, par un système p conjugué, représente une approche très flexible pour en moduler les propriétés optiques. Selon la nature du métal utilisé, il est possible de favoriser sélectivement la population d'états excités de nature et de multiplicité différentes. Notamment, la chélation de métaux lourds, comme le ruthénium(II), offre la possibilité d'accéder aux états triplets et d'en exploiter la richesse de propriétés.We report the design and synthesis of newly conjugated ligands based on pyrene as fluorescent group and 2,2'-bipyridine as chelating unit. These two groups are covalently assembled by an oligo(vinylene-phenylene) or oligo(ethynylene-phenylene) group. Photophysical investigation have underlined a dramatic modulation of the optical properties of these ligands upon addition of cations. Indeed, complexation of a metal ion, by a conjugated p system, provides a flexible way to tune the photophysical characteristics of this kind of compounds. Depending on the ion used, it is possible to populate excited states of different kind and spin multiplicity. Particularly, complexation of heavy metals, like ruthenium(II), provides an easy way to access triplet excited states

Nouvelles fonctionnalisations du noyau 1,10-phénanthroline : vers de nouveaux systèmes donneuraccepteur incorporant le tétrathiafulvalène

Date du colloque&nbsp;: 05/2008</p

Metal Ion Enhanced Charge Transfer in a Terpyridine-bis-Pyrene System

The synthesis, electrochemical and photophysical properties of a branched molecule 3,5-bis(pyrene-1-yl)-4′-phenyl-2,2′:6′,2″-terpyridine are reported. Spectroscopy in different solvents reveals that an optical electron transfer from the pyrene donor to the terpyridyl electron acceptor can occur in polar media, as the system displays both charge transfer (CT) absorption and CT emission. Furthermore, the study of the zinc complex as well as the bis-protonated form shows an enhancement of the electron transfer character of the system, by an increase of the acceptor strength. This is accompanied by a large increase of the non-radiative processes. With sub-nanosecond transient absorption spectroscopy, the CT state, consisting of the pyrene radical cation and the terpyridine radical anion, has been detected. At room temperature, the study of the nanosecond transient absorption spectra reveals the formation of a low-lying triplet excited state that we attribute to the pyrene moiety through which the CT state decays. At 77K, the absence of the terpyridine triplet emission also suggests the population of a low-lying triplet state of the pyrene unit

Synthesis of Perylene-3,4-mono(dicarboximide)−Fullerene C60 Dyads as New Light-Harvesting Systems

Fullerene C60−perylene-3,4-mono(dicarboximide) (C60−PMI) dyads 1−3 were synthesized in the search for new light-harvesting systems. The synthetic strategy to the PMI intermediate used a cross-coupling Suzuki reaction for the introduction of a formyl group in the ortho, meta, or para position. Subsequent 1,3-dipolar cycloaddition with C60 led to the target C60−PMI dyad. Cyclic voltammetry showed that the first one-electron reduction process unambiguously occurs onto the C60 moiety and the following two-electron process corresponds to the concomitant second reduction of C60 and the first reduction of PMI. A quasi-quantitative quenching of fluorescence was shown in dyads 1−3, and an intramolecular energy transfer was suggested to occur from the PMI to the fullerene moiety. These C60−PMI dyads constitute good candidates for future photovoltaic applications with expected well-defined roles for both partners, i.e., PMI acting as a light-harvesting antenna and C60 playing the role of the acceptor in the photoactive layer

Fullerene C60–Perylene-3, 4: 9, 10-bis (dicarboximide) Light-Harvesting Dyads: Spacer-Length and Bay-Substituent Effects on Intramolecular Singlet and Triplet Energy Transfer

Novel covalent fullerene C60-perylene-3,4:9,10-bis(dicarboximide) (C60-PDI) dyads (1-4) were synthesized and characterized. Their electrochemical and photophysical properties were investigated. Electrochemical studies show that the reduction potential of PDI can be tuned relative to C60 by molecular engineering through altering the substituents on the PDI bay region. It was demonstrated using steady-state and time-resolved spectroscopy that a quantitative, photoin-duced energy transfer takes place from the PDI moiety, acting as a light-harvesting antenna, to the C60 unit, playing the role of energy acceptor. The bay-substitution (tetrachloro [1 and 2] or tetra-tert-butylphenoxy [3 and 4]) of the PDI antenna and the linkage length (C2 [1 and 3] or C5 [2 and 4]) to the C60 acceptor are important parameters in the kinetics of energy transfer. Femtosecond transient absorption spectroscopy indicates singlet-singlet energy-transfer times (from the PDI to the C60 unit) of 0.4 and 5 ps (1), 4.5 and 27 ps (2), 0.8 and 12 ps (3), and 7 and 50 ps (4), these values being ascribed to two different conformers for each C60-PDI system. Subsequent triplet-triplet energy-transfer times (from the C60 unit to the PDI) are slower and in the order of 0.8 ns (1), 6.2 ns (2), 2.7 ns (3), and 9 ns (4). Nanosecond transient absorption spectroscopy of final PDI triplet states show a marked influence of the bay substitution (tetrachloro- or tetra-tert-butylphenoxy), and triplet-state lifetimes (10-20 μs) and the PDI triplet quantum yields (0.75-0.52) were estimated. The spectroscopy showed no substantial solvent effect upon comparing toluene (non-polar) to benzonitrile (polar), indicating that no electron transfer is occurring in these systems

Efficient singlet oxygen photogeneration by zinc porphyrin-dimers upon one- and two-photon excitation

Funding: UK EPSRC (EP/L017008/1), IDWS acknowledges a Royal Society Wolfson Research Merit Award. This work is a part of the ITN-EJD-2017 project POLYTHEA which has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement 764837.The development of photodynamic therapy at depth requires photosensitizers which have both sufficient quantum yield for singlet oxygen generation and strong two photon absorption. Here we show that this can be achieved by conjugated linkage of zinc porphyrins to make dimers. We determined the quantum yield of generation of 1O2, φΔ , by measuring emission at 1270 nm using a near infra-red streak camera and found it to increase from 15% for a single porphyrin unit to 27 47% for the dimers with a conjugated linker. Then, we measured the spectra of two-photon absorption cross section, σ2, by a focus-tunable Z scan method, which allows for nondestructive investigation of light-sensitive materials. We observed a strong enhancement of the two photon absorption coefficient in the dimers, especially those with an alkyne linker. These results lead to an excellent figure of merit for two photon production of singlet oxygen (expressed by the product σ2xφΔ) in the porphyrin dimers, of around 3700 GM, which is very promising for applications involving treatment of deep tumors by photodynamic therapy.PostprintPeer reviewe