Donor-acceptor Ensembles Research Articles

Topological Effects of a Rigid Chiral Spacer on the Electronic Interactions in Donor–Acceptor Ensembles

Two triads (donor-spacer-acceptor), exTTF-BN-C60 (6) and ZnP-BN-C60 (7), in which electron donors (i.e., exTTF or ZnP) are covalently linked to C60 through a chiral binaphthyl bridge (BN), have been prepared in a multistep synthetic procedure starting from a highly soluble enantiomerically pure binaphthyl building block (1). Unlike other oligomeric bridges, with binaphthyl bridges, the conjugation between the donor and the acceptor units is broken and geometric conformational changes are facilitated. Consequently, distances and electronic interactions between the donor and C60 are drastically changed. Both donor-spacer-acceptor (D-s-A) systems (i.e., 6 and 7) exhibit redox processes that correspond to all three constituent electroactive units, namely, donor, BN, and C60. Appreciable differences were, however, observed when comparing triad 6, in which no significant exTTF-C60 interactions were noted, with D-s-A 7, whose geometry favors donor-acceptor and pi-pi interactions that result in ZnP-C60 electronic communication. This through-space interaction is, for example, reflected in the redox potentials. Excited-state studies, carried out by fluorescence and transient absorption spectroscopy, also support through-space rather than through-bond interactions. Although both triads form the corresponding radical-ion pair, that is, exTTF*+-BN-C60*- and ZnP*+-BN-C60*-, dramatic differences were found in their lifetimes: 165 micros and 730 ns, respectively.

Hydrogen‐Bonding Motifs in Fullerene Chemistry

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Fluorinated Fullerenes: Sources of Donor−Acceptor Dyads with [18]Trannulene Acceptors for Energy- and Electron-Transfer Reactions

Fine-tuned control over the donor strength in a series of trannulenes-based donor-acceptor ensembles is used to alter the deactivation path of the photoexcited-state chromophore and to modulate the rates of intramolecular electron transfer. For the first time, a detailed analysis of emission spectra, time-dependent spectroscopic measurements, and electrochemistry prove spectroscopically and kinetically that trannulenes can serve, in a manner similar to C(60) and C(60) monoadducts, as both electron and also as energy acceptor in donor-acceptor ensembles, producing widely different electron-transfer regimes. This investigation also shows that the integration of trannulenes, as a versatile electron-acceptor building block, consistently produces charge recombination in the inverted Marcus region.

Hydrogen‐Bonding Motifs in Fullerene Chemistry

The combination of fullerenes and hydrogen-bonding motifs is a new interdisciplinary field in which weak intermolecular forces allow modulation of one-, two-, and three-dimensional fullerene-based architectures and control of their function. This Minireview aims to extend the scope of fullerene chemistry to a truly supramolecular level from which unprecedented architectures may evolve. It is shown that electronic communication in C(60)-based hydrogen-bonded donor-acceptor ensembles is at least as strong as that found in covalently connected systems and that hydrogen-bonding fullerene chemistry is a versatile concept for the construction of functional ensembles.

Materials for Organic Solar Cells: The C60/π‐Conjugated Oligomer Approach

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Materials for organic solar cells: the C60/π-conjugated oligomer approach

This tutorial review surveys recent advances in the field of C60/pi-conjugated oligomer donor-acceptor ensembles. In particular, different synthetic strategies are discussed that were developed to link pi-conjugated oligomers, as versatile photoexcited state electron donors, to C60. We highlight relationships between the nature/structural aspects of pi-conjugated donor systems and a variety of physico-chemical features. Modifications of the oligomeric components are discussed under aspects of tailoring (i) the absorption cross-section of the chromophore in the visible region, (ii) the oxidation potential of the oligomeric donor moiety, (iii) the size, shape, or chemical makeup of the oligomer, and (iv) the stabilization of the charge-separated radical ion pairs. In the final section, the applicability of selected materials for the fabrication of photovoltaic devices is analyzed.

Mimicking photosynthesis: covalent [60]fullerene-based donor–acceptor ensembles

Within the context of exploring photophysical properties of [60]fullerene-based donor–acceptor ensembles, we highlight in this contribution an approach towards the synthesis of a novel series of donor-bridge-acceptor, C60–wire–exTTF, ensembles that incorporate p-phenylenevinylene oligomers, in which the conjugation length has been systematically increased, as bridges that connect π-extended tetrathiafulvalenes (exTTF) (electron donor) with [60]fullerene (electron acceptor). This molecular design allows probing the effects of distance and rate, at which electron transfer processes occur, as well as the molecular-wire behavior of the oligo-PPV fragments.

Comparative studies of the spectra and the second-order nonlinear polarizabilities for donor–acceptor ensembles between Zn-porphyrin/fullerene [60] and Zn-porphyrin/naphthalenediimide

A series of donor–acceptor ensembles with fullerene [60] and naphthalenediimide (NIm) as acceptors and Zn-porphyrin (ZnP) as donors have been theoretically studied. The donors and acceptors are separated by different rigid bridges (–CC–, –CONH– and –NHCO–). Their equilibrium geometries and UV–Visible spectra were calculated by means of INDO/2 and the INDO/CI methods. The calculated results indicated that the charge transfer from the donor—Zn-porphyrin to the acceptor takes place for the ensembles with fullerene [60] as acceptors while for the molecules with NIm as acceptors, charge transfer is weak. On the basis of correct electronic spectra, calculations of the nonlinear second-order optical polarizabilites β ijk and β μ values were carried out using the INDO/CI method combined with a Sum-Over-States (SOS) expression. We conclude that the bridge of –NHCO– leads to comparatively large nonlinear second-order polarizability than the other two bridges; and the 3D fullerene [60] acceptor is superior to the 2D NIm acceptor due to its symmetrical shape, large size, and properties of its π-electron system. We illustrate the phenomena by means of the comparison of the frontier orbitals and net charge in the ground and main excited states.

Electron Transfer in Electron Donor—Acceptor Ensembles Containing Porphyrins and Metalloporphyrins

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Electron transfer in electron donor-acceptor ensembles containing porphyrins and metalloporphyrins

Recent advances in electron transfer chemistry of electron donor-acceptor ensembles reported containing porphyrins and metalloporphyrins reported in ICPP-2 are reviewed briefly by focusing on the fundamental aspects of electron transfer reactions.

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.

Self-organisation in photoactive fullerene porphyrin based donor–acceptor ensembles

Complexation of ZnP-C60-ZnP triads with diazabicyclooctane (DABCO) leads to rigid assemblies that display considerably prolonged charge-separated states.