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

Abstract

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.

Multi‐Electron‐Acceptor Dyad and Triad Systems Based on Perylene Bisimides and Fullerenes

“…[11][12][13][14] The majority of these studies differ significantly from our study in that the fullerene moiety is attached to the PTCDI group by means of the imide nitrogen. [11][12][13] Molecular orbital calculations on PTCDI derivatives reveal a node in the HOMO at the nitrogen atoms of the imide functions, precluding electronic communication pathways between imide appendages and the fullerene. [23] Of additional importance is the group used to functionalise the fullerene moiety.…”

Efficient Photoinduced Energy Transfer Mediated by Aromatic Homoconjugated Bridges

“…3 + complex in acetonitrile after laser excitation at 370 nm; [23] several processes can be observed. Positive transient absorptions are shown in light grey shades, while negative bands are represented by dark grey.…”

“…[23] The full spectrum setup was based on an optical parametric amplifier (Spectra-Physics OPA 800C) as the pump. The residual fundamental light, from the pump OPA, was used for white-light generation, which was detected with a CCD spectrograph (Ocean Optics PC2000 + slave) for Vis detection.…”

An overview of molecular acceptors for organic solar cells

“…The principle of associating a dye attached to the fullerene was proposed to reach C 60 -PBI or C 60 -PMI dyads as super-absorbing fullerenes (Fig. 11) [84][85][86][87]. Even if the PCE were low using this dyad as an acceptor, the role of the perylenebisimide (PBI) acting as a light-harvesting antenna was evidenced by an efficient intramolecular energy transfer occurring from PBI onto C 60 and the relationship between electrochemical properties of the dyad and the P3HT: C 60 -PBI blend efficiency was evidenced [88].…”