Electric field dependent photocurrent generation in a thin-film organic photovoltaic device with a [70]fullerene-benzodifuranone dyad.

A [70]fullerene-benzodifuranone acceptor dyad synthesized by a Ag⁺-mediated coupling reaction was used to construct a thin-film organic solar cell. The fullerene and the benzodifuranone dye in the dyad have close-lying LUMO levels in the range of 3.7-3.9 eV, so that energy transfer from the dye to the fullerene can take place. A p-n heterojunction photovoltaic device consisting of a tetrabenzoporphyrin and a [70]fullerene-benzodifuranone dyad showed a weak but discernible contribution from light absorption of the dyad to the photocurrent under both a positive and a negative effective bias. These results indicate that the benzodifuranone moiety attached to the acceptor contributes to light-harvesting by energy transfer.

Enzyme mimics based upon supramolecular coordination chemistry.

Recent advances in supramolecular coordination chemistry have allowed chemists to synthesize macromolecular complexes that exhibit various properties intrinsic to enzymes. This Review focuses on structures inspired by properties and functions observed in enzymes rather than precise models of enzyme active sites. These structures are synthesized using convergent, modular, and high-yielding coordination-chemistry-based methods, which allow one to tailor the size, shape, and properties of the resulting complexes. Many of the structures discussed exhibit reactivity and specificity reminiscent of natural systems, and some of them have functions that exceed the natural systems which provided the inspiration for initially making them.

Selective formation of heteroligated Pt(II) complexes with bidentate phosphine-thioether (P,S) and phosphine-Selenoether (P,Se) ligands via the halide-induced ligand rearrangement reaction.

Bidentate phosphine-selenoether (P,Se) ligands were synthesized, and their heteroligated Pt(II) complexes were made and studied. The unique "P,S/P,Se" ligand coordination to Pt(II) can be realized via the halide-induced ligand rearrangement reaction. In all cases, the exclusive formation of semi-open heteroligated complexes was achieved as shown by (31)P and (77)Se NMR spectroscopy and from single crystal X-ray diffraction studies. This is the first example of the use of (77)Se NMR spectroscopy to characterize these types of structures through direct observation of the weak-link interaction with the metal center. Heteroligated structure formation is believed to be driven by the relative electron-donating ability of the substituent groups on the seleno or thioether moieties. This effect is studied by comparing the structures of corresponding "P,SMe" and "P,SeMe" complexes bearing a hemilabile "P,SCH(2)CF(3)" group, which is less sterically demanding than "P,SPh" but is similar in terms of electron withdrawing ability.

Heteroligated supramolecular coordination complexes formed via the halide-induced ligand rearrangement reaction.

Supramolecular coordination chemistry allows researchers to synthesize higher-order structures that approach the nanoscale dimensions of small enzymes. Frequently, such structures have highly symmetric macrocyclic square or cage shapes. To build functional structures that mimic the complex recognition, catalytic, and allosteric properties of enzymes, researchers must do more than synthesize highly symmetric nanoscale structures. They must also simultaneously incorporate different functionalities into these structures and learn how to regulate their relative arrangement with respect to each other. Designing such heteroligated coordination complexes remains a significant challenge for supramolecular chemists. This Account focuses on the discovery and development of a novel supramolecular reaction known as the halide-induced ligand rearrangement (HILR) reaction. Two hemilabile ligands with different binding strengths combine with d(8) transition metal precursors that contain halide ions. The reaction spontaneously results in heteroligated complexes and is highly modular and general. Indeed, it not only can be used to prepare tweezer complexes but also allows for the rapid and quantitative formation of heteroligated macrocyclic triple-decker/step and rectangular box complexes from a variety of different ligands and transition metal ions. The relative arrangement between functional groups A and B in these structures can be regulated in situ using small ancillary ligands such as halides, CO, and nitriles. Based on this reaction, zinc- and magnesium-porphyrin moieties can be incorporated into heteroligated macrocyclic or tweezer scaffolds. These examples demonstrate the convergent and cofacial assembly of functional sites that are known to be involved in numerous processes in enzymes. They also show how the relative spatial and lateral distances of these sites can be varied, in many cases reversibly. Researchers can use such complexes to study a wide range of enzymatic processes, including catalysis, molecular recognition, electron transfer, and allosteric signal transfer.

Reversible Ligand Pairing and Sorting Processes Leading to Heteroligated Palladium(II) Complexes with Hemilabile Ligands.

Halide-induced ligand pairing and sorting processes have been observed in the context of Pd(II) complexes with hemilabile P,S and P,O ligands. Mixing of the ligands Ph2PCH2CH2SMe (7) and Ph2PCH2CH2SPh (8) with a Pd(II) precursor in CH2Cl2 results in a mixture of [(7)2ClPd]Cl, [(8)2Cl2Pd], and [(7)(8)ClPd]Cl complexes at 20 °C. This equilibrium can be driven toward the heteroligated structure [(7)(8)ClPd]Cl by (1) cooling the mixture or (2) precipitation with hexanes, leading to the exclusive formation of semiopen heteroligated complex cis-[κ 2-(7)-κ 1-(8)ClPd]Cl (9a), as confirmed by a single-crystal X-ray diffraction study and solid state CPMAS 31P{1H} NMR spectroscopy. Dissolution of 9a in CH2Cl2 leads to the original mixture of complexes, which illustrates the reversible nature of this ligand pairing and sorting process. Similar processes occur when a combination of P,S and P,O ligands is used. The semiopen heteroligated complexes can be chemically manipulated in a reversible fashion to form closed complexes, allowing for control of the relative position and flexibility between neighboring substituents in these "tweezer"-like structures. Control experiments suggest these ligand sorting and pairing processes occur via a halide-induced ligand rearrangement (HILR) reaction.

Inversion of product selectivity in an enzyme-inspired metallosupramolecular tweezer catalyzed epoxidation reaction.

This study describes a heteroligated, hemilabile Pt(II)-P,S tweezer coordination complex that combines a chiral Jacobsen-Katsuki Mn(III)-salen epoxidation catalyst with an amidopyridine receptor, which leads to an inversion of the major epoxide product compared to catalysts without a recognition group.

A DNA-gold nanoparticle-based colorimetric competition assay for the detection of cysteine.

We report the development of a highly sensitive and selective colorimetric detection method for cysteine based upon oligonucleotide-functionalized gold nanoparticle probes that contain strategically placed thymidine-thymidine (T-T) mismatches complexed with Hg2+. This assay relies upon the distance-dependent optical properties of gold nanoparticles, the sharp melting transition of oligonucleotide-linked nanoparticle aggregates, and the very selective coordination of Hg2+ with cysteine. The concentration of cysteine can be determined by monitoring with the naked eye or a UV-vis spectrometer the temperature at which the purple-to-red color change associated with aggregate dissociation takes place. This assay does not utilize organic cosolvents, enzymatic reactions, light-sensitive dye molecules, lengthy protocols, or sophisticated instrumentation thereby overcoming some of the limitations of more conventional methods.

Spontaneous formation of heteroligated PtII complexes with chelating hemilabile ligands.

The spontaneous formation of the heteroligated complex [PtCl(kappa(2)-Ph(2)PCH(2)CH(2)SMe)(Ph(2)PCH(2)CH(2)SPh)]Cl (8 a) by a novel ligand rearrangement process has been observed. By using the weak-link approach, the relative arrangement of the alkyl and aryl groups can be controlled by abstraction of chloride from 8 a to form the closed complex [Pt(kappa(2)-Ph(2)PCH(2)CH(2)SMe)(kappa(2)-Ph(2)PCH(2)CH(2)SPh)][BF(4)](2) (5) and reopening using halide ions to form semi-open complexes [PtX(kappa(2)-Ph(2)PCH(2)CH(2)SMe)(Ph(2)PCH(2)CH(2)SPh)]BF(4) (8 b; X=Cl(-)) and (8 c; X=I(-)). Analogous procedures using Ph(2)PCH(2)CH(2)SMe and 1,4-(Ph(2)PCH(2)CH(2)S)(2)C(6)H(4) lead to heteroligated bimetallic complexes 7 and 9, illustrating that this ligand rearrangement process can be used as a tool for the assembly of complementary metallosupramolecular structures.