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

New fluorescent perylene bisimide indicators—a platform for broadband pH optodes

Asymmetric perylene bisimide (PBI) dyes are prepared and are shown to be suitable for the preparation of fluorescence chemosensors for pH. They carry one amino-functional substituent which introduces pH sensitivity via photoinduced electron transfer (PET) while the other one increases solubility. The luminescence quantum yields for the new indicators exceed 75% in the protonated form. The new indicators are non-covalently entrapped in polyurethane hydrogel D4 and poly(hydroxyalkylmethacrylates). Several PET functions including aliphatic and aromatic amino groups were successfully used to tune the dynamic range of the sensor. Because of their virtually identical spectral properties, various PBIs with selected PET functions can easily be integrated into a single sensor with enlarged dynamic range (over 4 pH units). PBIs with two different substitution patterns in the bay position are investigated and possess variable spectral properties. Compared with their tetrachloro analogues, tetra-tert-butyl-substituted PBIs yield more long-wave excitable sensors which feature excellent photostability. Cross-sensitivity to ionic strength was found to be negligible. The practical applicability of the sensors may be compromised by the long response times (especially in case of tetra-tert-butyl-substituted PBIs)

Superabsorbing fullerenes: Spectral and kinetic characterization of photoinduced interactions in perylenediimide-fullerene-C-60 dyads

Two n-type molecular materials are covalently combined into a new photovoltaic component for polymer solar cells. Light harvesting by the perylenediimide results in very fast energy transfer to the fullerene unit, as shown with femtosecond transient absorption spectroscopy in toluene solution. Two energy transfer rates are observed of 2.5 × 1

Light-harvesting fullerenes for organic solar cells

Novel dyads containing [60]fullerene-perylenediimide units were developed as light-harvesting acceptors for the preparation of efficient solar cells. The antenna was grafted onto C-60 with the aim to improve the absorption spectrum of materials used in bulk-heterojunction devices. Electrochemical and photophysical studies of these dyads in solution have revealed that there was no significant ground-state electronic interaction between the covalently bonded PDI and fullerene moieties. Steady-state fluorescence experiments evidenced an effective photoinduced energy transfer from the PDI moiety to C-60. The potential use of these light-harvesting fullerenes in organic solar cells was estimated with their incorporation in bulk-heterojunctions using poly(3-hexylthiophene) as the conjugated pi-donor polymer