Stéphanie Leroy-Lhez

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 C(60)-perylene-3,4:9,10-bis(dicarboximide) (C(60)-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 C(60) 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, photoinduced energy transfer takes place from the PDI moiety, acting as a light-harvesting antenna, to the C(60) 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 (C(2) [1 and 3] or C(5) [2 and 4]) to the C(60) 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 C(60) 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 C(60)-PDI system. Subsequent triplet-triplet energy-transfer times (from the C(60) 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 micros) 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.

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

Fullerene C 60-perylene-3,4-mono(dicarboximide) (C 60-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 C 60 led to the target C 60-PMI dyad. Cyclic voltammetry showed that the first one-electron reduction process unambiguously occurs onto the C 60 moiety and the following two-electron process corresponds to the concomitant second reduction of C 60 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 C 60-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 C 60 playing the role of the acceptor in the photoactive layer.

Synthesis and zinc(II) complexation modulated fluorescence emission properties of two pyrene-oligo(phenylene vinylene)-2,2′-bipyridine conjugated molecular rods

A series of conjugated rods in which the pyrene chromophore is connected to a 2,2′-bipyridine unit via an oligo(phenylene vinylene) bridge have been synthesized and their photophysical properties in solution investigated. They are shown to display intense visible electronic absorption and fluorescence emission properties. The excited-states characteristics are compared to analogous systems containing an oligo(phenylene ethynylene) spacer. The zinc complexes of the new molecules possess very polar excited states, which lead to strong solvatochromic shifts. Semi empirical calculations were performed which confirmed the experimental data. The X-ray analysis of a pyrene-containing π-conjugated bipyridine ligand is described.

Vibrational and Electronic Properties of Perylenediimide Linked to Fullerene and Tetrathiafulvalene

Solid-state electronic (UV-Vis) and vibrational (IR) spectra of the tetrathiafulvalene-perylenediimide (PDI-TTF) 1 and perylenediimide-fullerene (PDI-C60) 2 dyads as well as PDI 3 , TTF 8 and fullerene 9 derivatives used as references molecules were investigated in the frequency range between 400 and 45,500 cm−1. Electronic and vibrational features of the dyads were compared and analysed. Molecular geometry of the compounds and their IR and Raman theoretical spectra were calculated. It was stated, that small redistribution of the charges occurs in both moieties of these dyads. This effect is observed as shifts of both electronic and vibrational bands of the dyads in comparison with the respective bands of free components.

Synthesis and conformation of a novel fluorescein–Zn-porphyrin dyad and intramolecular energy transfer

This study describes the synthesis and characterization of a new zinc porphyrin–fluorescein dyad, the two chromophoric units being covalently linked by a 1,2,3-triazole bridge. The latter was formed by Cu-catalyzed Huisgen 1,3-dipolar cycloaddition. The conformational analysis of this dyad (1) was performed by NOESY experiments, suggesting interactions between moieties; density functional theory (DFT) calculations confirmed clear evidence of a folded conformer, which is stabilized by electrostatic and CH–π interactions. Photophysical measurements demonstrated solvent-dependent energy transfer, with an efficiency of about 40%.