Electrostatic complexation and photoinduced electron transfer between Zn-cytochrome c and [olyanionic fullerene dendrimers

Two dendritic fullerene (DF) monoadducts, 2 and 3, which can carry up to 9 and 18 negative charges, respectively, were examined with respect to electrostatic complexation with Cytochrome c (Cytc). To facilitate comprehensive photophysical investigations, the zinc analogue of Cytc (ZnCytc) was prepared according to a novel, modified procedure. The association of ZnCytc and DF, and consequential photoinduced electron transfer within ZnCytc-DF from the photoexcited protein to the fullerene, was proven by fluorescence spectroscopy and transient absorption spectroscopy. These findings were also supported by circular dichroism as well as by extensive molecular dynamics (MD) simulations.     

Thermally reversible C60-based donor-acceptor ensembles

Diels-Alder cycloaddition of anthracene derivatives--bearing fused pi-extended TTFs--to C60 yielded thermally reversible donor-acceptor materials which function as fluorescence switches.     

Panchromatic light funneling through the synergy in hexabenzocoronene–(metallo)porphyrin–fullerene assemblies to realize the separation of charges

Here, we present a novel butadiyne-linked HBC-ethynyl-porphyrin dimer, which exhibits in the ground state strong absorption cross sections throughout the UV and visible ranges of the solar spectrum. In short, a unidirectional flow of excited state energy from the HBC termini to the (metallo)porphyrin focal points enables concentrating light at the latter. Control over excitonic interactions within, for example, the electron-donating porphyrin dimers was realized by complexation of bidentate ligands to set up panchromatic absorption that extends all the way into the near-infrared range. The bidentate binding motif was then exploited to create a supramolecular electron donor–acceptor assembly based on a HBC-ethynyl-porphyrin dimer and an electron accepting bis(aminoalkyl)-substituted fullerene. Of great relevance is the fact that charge separation from the photoexcited HBC-ethynyl-porphyrin dimer to the bis(aminoalkyl)-substituted fullerene is activated not only upon photoexciting the HBCs in the UV as well as the (metallo)porphyrins in the visible but also in the NIR. Implicit is the synergetic interplay of energy and charge transfer in a photosynthetic mimicking manner. The dimer and bis-HBC-ethynyl-porphyrin monomers, which serve as references, were probed by means of steady-state as well as time-resolved optical spectroscopies, including global target analyses of the time-resolved transient absorption data.

Here, we present a novel butadiyne-linked HBC-ethynyl-porphyrin dimer, which exhibits in the ground state strong absorption cross sections throughout the UV and visible ranges of the solar spectrum.     

Photoactive preorganized subphthalocyanine-based molecular tweezers for selective complexation of fullerenes

The development of new chromophoric receptors capable of binding curved carbon nanostructures is central to the quest for improved fullerene-based organic photovoltaics. We herein report the synthesis and characterization of a subphthalocyanine-based multicomponent ensemble consisting of two electron-rich SubPc-monomers rigidly attached to the convex surface of an electron-poor SubPc-dimer. Such a unique configuration, especially in terms of the two SubPc-monomers, together with the overall stiffness of the linker, endows the multicomponent system with a well-defined tweezer-like topology to efficiently embrace a fullerene in its inner cavity. The formation of a 1 : 1 complex was demonstrated in a variety of titration studies with either C60 or C70. In solution, the underlying association constants were of the order of 10⁵ M⁻¹. Detailed physicochemical experiments revealed a complex scenario of energy- and electron-transfer processes upon photoexcitation in the absence and presence of fullerenes. The close proximity of the fullerenes to the electron-rich SubPcs enables a charge shift from the initially formed reduced SubPc-dimer to either C60 to C70.

A tweezer-like subphthalocyanine-based ensemble has been developed for the selective recognition of fullerenes. The physicochemical properties of both the photoactive receptor and its inclusion complexes with fullerenes have been investigated.     

Synthesis and photophysical characterization of a titanium(IV) phthalocyanine-C60 supramolecular dyad

An axially substituted titanium(IV) phthalocyanine-fullerene donor-acceptor supramolecular dyad has been prepared by two different approaches, one of them representing a convenient convergent strategy. The dyad system exhibits photoinduced electron transfer upon irradiation with visible light to produce a microsecond lived charge separated state.     

Small reorganisation energy and unique stabilisation of zwitterionic C60-acceptor moieties

Fulleropyrrolidine- and fulleropyrrolidinium-based donor-acceptor ensembles, C60-Fc, were tested in view of intrinsic reorganisation energies for light-induced electron transfer events; overall, the zwitterionic character of the reduced fulleropyrrolidinium acceptor plays a central role in accelerating charge separation and decelerating charge recombination.     

Through bond mechanism versus exciplex formation in the photochemistry of fullerene / ferrocene donor-bridge-acceptor dyads

A systematic fluorescence and flash photolytic investigation of a series of covalently linked fullerene / ferrocene based donor-bridge-acceptor dyads is reported as a function of the nature of the bridge between the donor site and acceptor site. The fluorescence of the investigated dyads 2 (Φ_rel = 0.17 × 10^?4, 3 (Φ_rel = 0.78 × 10^?4), 4 (Φ_rel = 1.5 × 10^?4), 5 (Φ_rel = 0.7 × 10^?4), and 6 (Φ_rel = 2.9 × 10^?4) were substantially quenched, relative to N-methyl fulleropyrrolidine (1) (Φ_rel = 6.0 × 10^?4). Photolysis of N-methyl fulleropyrrolidine (1) in toluene revealed formation of the excited singlet state which was followed by a rapid intersystem crossing to the excited triplet state. On the other hand, the fate of the excited singlet state of 2, 3, 4, 5, and 6 was found to be governed by rapid intramolecular quenching, with rate constants of 28×10⁹ s^?1, 6.9×10⁹ s^?1, and 3.4×10⁹ s^?1, 14×10⁹ s^?1, 2.3×10⁹ s^?1 respectively. The electron transfer process and the charge separation were confirmed by monitoring the characteristic π-radical anion bands at λ_max = 400 and 1055 nm in degassed benzonitrile with τ_1/2 = 1.8 μs (3) and 2.5 μs (4).     

Hydrogen bond-assembled fullerene molecular shuttle

A novel [2]rotaxane has been prepared in which fullerene C(60) behaves as both a stopper and a photoactive unit. The amphiphilic nature of the rotaxane thread can be used to shuttle the macrocycle from close to the fullerene spheroid (in nonpolar solvents) to far away (in polar solvents). The differing location of the macrocycle in dichloromethane and dimethyl sulfoxide gives rise to effects detectable by (1)H NMR and time-resolved spectroscopy.