A New Iterative Approach for the Synthesis of Oligo(phenyleneethynediyl) Derivatives and Its Application for the Preparation of Fullerene?Oligo(phenyleneethynediyl) Conjugates as Active Photovoltaic Materials

Nucleophilic cyclopropanation of [60]fullerene by the addition–elimination mechanism

Information on the synthesis of monofunctionalized methanofullerenes C₆₀ obtained by the addition–elimination mechanism is generalized. The main reagents for cyclopropanation, mechanisms and optimal conditions for the processes, and the prospects for practical application of the products are considered.

Generalized material on the synthesis of monosubstituted methanofullerenes C₆₀, obtained by the addition–elimination mechanism.

Emerging Photovoltaics: Organic, Copper Zinc Tin Sulphide, and Perovskite-Based Solar Cells

As the photovoltaics industry continues to grow rapidly, materials other than silicon are being explored. The aim is to develop technologies that use environmentally friendly, abundant materials, low-cost manufacturing processes without compromising on efficiencies and lifetimes. This paper discusses three of the emerging technologies, organic, copper zinc tin sulphide (CZTS), and perovskite-based solar cells, their advantages, and the possible challenges in making these technologies commercially available.

Oligo(p-phenylene-ethynylene)-derived super-π-gelators with tunable emission and self-assembled polymorphic structures

Linear π-conjugated oligomers are known to form organogels through noncovalent interactions. Herein, we report the effect of π-repeat units on the gelation and morphological properties of three different oligo(p-phenylene-ethynylene)s: OPE3, OPE5, and OPE7. All of these molecules form fluorescent gels in nonpolar solvents at low critical gel concentrations, thereby resulting in a blue gel for OPE3, a green gel for OPE5, and a greenish yellow gel for OPE7. The molecule-molecule and molecule-substrate interactions in these OPEs are strongly influenced by the conjugation length of the molecules. Silicon wafer suppresses substrate-molecule interactions whereas a mica surface facilitates such interactions. At lower concentrations, OPE3 formed vesicular assemblies and OPE5 gave entangled fibers, whereas OPE7 resulted in spiral assemblies on a mica surface. At higher concentrations, OPE3 and OPE5 resulted in super-bundles of fibers and flowerlike short-fiber agglomerates when different conditions were applied. The number of polymorphic structures increases on increasing the conjugation length, as seen in the case of OPE7 with n=5, which resulted in a variety of exotic structures, the formation of which could be controlled by varying the substrate, concentration, and humidity.

Polar tagging in the synthesis of monodisperse oligo(p-phenyleneethynylene)s and an update on the synthesis of oligoPPEs

One important access to monodisperse (functionalized) oligoPPEs is based on the orthogonality of the alkyne protecting groups triisopropylsilyl and hydroxymethyl (HOM) and on the polar tagging with the hydroxymethyl moiety for an easy chromatographic separation of the products. This paper provides an update of this synthetic route. For the deprotection of HOM protected alkynes, γ-MnO₂ proved to be better than (highly) activated MnO₂. The use of HOM as an alkyne protecting group is accompanied by carbometalation as a side reaction in the alkynyl-aryl coupling. The extent of carbometalation can be distinctly reduced through substitution of HOM for 1-hydroxyethyl. The strategy of polar tagging is extended by embedding ether linkages within the solubilising side chains. With building blocks such as 1,4-diiodo-2,5-bis(6-methoxyhexyl) less steps are needed to assemble oligoPPEs with functional end groups and the isolation of pure compounds becomes simple. For the preparation of 1,4-dialkyl-2,5-diiodobenzene a better procedure is presented together with the finding that 1,4-dialkyl-2,3-diiodobenzene, a constitutional isomer of 1,4-dialkyl-2,5-diiodobenzene, is one of the byproducts.

Recent advances in the design, synthesis and study of covalent conjugated oligomer–C60 ensembles

This review presents an overview of the most recent results in the field of conjugated oligomer covalently attached to the C60 sphere focusing mainly on donor–conjugated oligomer–C60 triads and conjugated oligomer–multifullerene materials. Well-defined monodisperse oligomers as new materials that exhibit interesting optoelectronic properties have been the subject of intense study during the last decade. In this regard, a huge amount of work has been devoted to the development of new synthetic strategies toward the synthesis of conjugated oligomeric materials with precise length and constitution and to their chemical functionalization in order to incorporate them into more complex molecular and supramolecular architectures. An important area of research in the field of conjugated oligomers involves the design and synthesis of donor–acceptor ensembles by combination of monodisperse π-conjugated oligomeric systems with C60 fullerene. Such hybrid systems have shown excited-state interactions making them excellent candidates for fundamental photophysical studies. In addition, these materials have found applications in the field of photovoltaic devices. A review with 70 references.

Dynamic [2]Catenanes Based on a Hydrogen Bonding-Mediated Bis-Zinc Porphyrin Foldamer Tweezer: A Case Study

This paper describes the self-assembly of a new class of three-component dynamic [2]catenanes, which are driven or stabilized by intramolecular hydrogen bonding, coordination, and electrostatic interaction. One of the component molecules 2, consisting of an aromatic oligoamide spacer and two peripheral zinc porphyrin units, was designed to adopt a folded preorganized conformation, which is stabilized by consecutive intramolecular three-centered hydrogen bonds. Component molecule 3 is a linear secondary ammonium bearing two peripheral pyridine units, which was designed to form a 1:1 complex with 24-crown-8 (5). The 1H NMR and UV-vis experiments in CDCl3-CD3CN (4:1 v/v) revealed that, due to the preorganized U-shaped feature, 2 could efficiently bind 3 through the cooperative zinc-pyridine coordination to generate highly stable 1:1 complex 2.3. Adding 5 to the 1:1 solution of 2 and 3 led to the formation of dynamic three-component [2]catenane 2.3.5 as a result of the threading of 3 through 5. 1H NMR studies indicated that in the 1:1:1 solution (3 mM) [2]catenane 2.3.5 was generated in 55% yield at 25 degrees C. The yield was increased with the reduction of the temperature and [2]catenane could be produced quantitatively in a 1:1:2 solution ([2]=3 mM) at -13 degrees C. Replacing 3 with 1,2-bis(4,4'-bipyridinium)ethane (4) in the three-component solution could also give rise to similar dynamic [2]catenane 2.4.5 albeit in slightly lower yield.

Resonance Energy Transfer in New Fullerene–Coumarin Diads

The fluorescence properties of new [60] and [70] fullerene-coumarin diads are studied. These diads were synthesized by covalently linking a coumarin dye to a fullerene (C60 or C70) by a cyclopropanation reaction. The absorption and fluorescence spectra, quantum yields and lifetimes of the diads are reported. The fluorescence quenching of the coumarin moiety by the fullerene was observed in all diads, indicating the occurrence of resonance energy transfer between the coumarin and fullerene moieties.

Photoinduced energy and electron transfer in fullerene–oligophenyleneethynylene systems: dependence on the substituents of the oligomer unit

The photophysical properties of fullerene hybrid systems in which disymmetrically substituted linear oligophenyleneethynylene (OPE) substituents have been attached to C(60) through a pyrrolidine ring are discussed. These hybrid systems differ in both the length of the conjugated OPE backbone and in the type of terminating groups employed, i.e. tri-isopropylsilane (-Si(iPr)(3)) and N,N-di-n-butylaniline (PhN(nBu)(2)). The terminating group is found to be crucial in determining the fate of light absorbed by the hybrid. In CH(2)Cl(2) and benzonitrile, the PhN(nBu)(2) terminated hybrids undergo electron transfer with charge separation lasting as long as 390 ns in the more polar medium, as detected via near-infrared transient absorption spectroscopy. Under the same conditions the Si(iPr)(3) terminated hybrids show ultrafast OPE --> C(60) singlet energy transfer (k = 10(9)-10(10) s(-1)) followed by regular deactivation of the C(60) moiety, as determined via UV-VIR-NIR steady state and time-resolved spectroscopy. Only in polar benzonitrile such systems can undergo electron transfer to some extent (40% yield). The results here presented can be readily explained in light of the electrochemical properties of the hybrids. The low oxidation potentials of the PhN(nBu)(2) terminated systems allow the formation of low lying charge separated states ( approximately 1.45 eV) which, in Si(iPr)(3) terminated analogues, are shifted substantially upward ( approximately 1.90 eV) and become hardly accessible via direct excitation or sensitization of the C(60) singlet level (1.72 eV). These results, when examined in light of the performance of photovoltaic devices using these hybrids as active materials, show a nice structure-activity relationship supporting the appeal of the so-called molecular approach to photovoltaic devices.

Tuning electron transfer through p-phenyleneethynylene molecular wires

Weak wire-like behavior-with a damping factor (beta) of 0.2 +/- 0.05 A(-1)--has been found in a series of C60-wire-exTTF systems (i.e., p-phenyleneethynylene): these results contrast with previous observations involving p-phenylenevinylene systems.

Synthesis and Optical Properties of Isomeric Branched π-Conjugated Systems

[structure: see text] Branched conjugated systems with a terminal alkyne function have been prepared starting from 4-(triisopropylsilylethynyl) phenylacetylene by applying the following iterative reaction sequence: (i) metal-catalyzed cross-coupling reaction of the terminal alkyne with 3,4-dibromobenzaldehyde or 2,5- dibromobenzaldehyde; (ii) Corey-Fuchs dibromoolefination and treatment with an excess of LDA. The building blocks thus prepared have been subjected to a Pd-catalyzed cross-coupling reaction with 1,4-diiodobenzene to yield isomeric branched pi-conjugated systems containing 7 (first generation) or 15 (second generation) phenyl units connected by ethynyl spacers. The different pi-conjugation patterns in those isomeric derivatives have a dramatic effect on their electronic properties, as attested by the differences observed in their absorption and emission spectra. Finally, theoretical calculations have been performed to rationalize the optical properties of these compounds.

Synthesis, Spectroscopic and Nonlinear Optical Properties of Multiple [60]Fullerene-Oligo(p-phenylene ethynylene) Hybrids

A series of multiple [60]fullerene terminated oligo(p-phenylene ethynylene) (OPE) hybrid compounds has been synthesized through a newly developed in situ ethynylation method. Structural and magnetic shielding properties of the highly unsaturated carbon-rich C(60) and OPE scaffolds were characterized by 1D and 2D NMR spectroscopic analyses. Electronic interactions between the [60]fullerenes and the OPE backbones were investigated by UV/Vis spectroscopic and cyclic voltammetry (CV) experiments. Our studies clearly show that although the multiple [60]fullerene groups are connected via pi-conjugated OPE frameworks, they present diminutive electronic interactions in the ground state, and the electronic behavior of the [60]fullerene cages are only affected by the OPE backbones through modest inductive effects. Interestingly, sizable third-order nonlinear optical (NLO) responses (gamma) and enhanced two-photon absorption (TPA) cross-sections (sigma((2))) were determined for the multifullerene-OPE hybrid 31 relative to its OPE precursor from differential optical Kerr effect (DOKE) experiments. Such enhanced NLO performance is presumably due to the occurrence of periconjugation and/or charge transfer effects in the excited state. In addition, comparatively strong excited-state absorption was observed and characterized for OPE pentamer 12. Thus, the use of such fullerene-derivatized conjugated oligomers aids the quest for molecules with large third-order NLO and TPA properties.

Pyrazolino[60]fullerene-Oligophenylenevinylene Dumbbell-Shaped Arrays: Synthesis, Electrochemistry, Photophysics, and Self-Assembly on Surfaces

Symmetrically substituted oligophenylenevinylene (OPV) derivatives bearing terminal p-nitrophenylhydrazone groups have been prepared and used for the synthesis of dumbbell-shaped bis(pyrazolino[60]fullerene)-OPV systems. In these triad arrays, the OPV-type fluorescence is dramatically quenched as a consequence of ultrafast OPV-->C60 singlet energy transfer. In its turn the fullerene singlet state is quenched by pyrazoline-->C60 electron transfer, in line with the behavior of the corresponding reference fullerene molecule. The occurrence of electron transfer in the multicomponent arrays is evidenced by recovery of fullerene fluorescence at 77 K in CH2Cl2 and in toluene at 298 K. Under these conditions the OPV-->C60 energy transfer is unaffected. The rate of this process turns out to be higher for the OPV trimer than for the corresponding pentameric OPV arrays, in agreement with energy-transfer theory expectations. Scanning tunneling microscopy (STM) and scanning force microscopy (SFM) revealed that the bis(pyrazolino[60]fullerene)-OPV can self-assemble into ordered layered crystalline architectures on the basal plane of highly oriented pyrolitic graphite.