Heteromeric guanosine (G)-quadruplex derived antenna modules with directional energy transfer.

A heteromeric guanosine (G)-quadruplex centered self-assembly approach is developed to prepare compact light-harvesting antenna modules featuring multiple donor dyes and a single toehold region. Due to the mix-and-match nature of our approach, the number and placement of donor dyes can be readily fine-tuned quadruplex assembly. Moreover, hybridization of the toehold with an acceptor containing sequence results in directional energy transfer ensembles with effective absorption coefficients in the 10 M cm range.

Bimolecular Excited-State Proton-Coupled Electron Transfer within Encounter Complexes.

Bimolecular excited-state proton-coupled electron transfer (PCET*) was observed for reaction of the triplet MLCT state of [(dpab)Ru(4,4'-dhbpy)] (dpab = 4,4'-di(-propyl)amido-2,2'-bipyridine, 4,4'-dhbpy = 4,4'-dihydroxy-2,2'-bipyridine) with -methyl-4,4'-bipyridinium (MQ) and -benzyl-4,4'-bipyridinium (BMQ) in dry acetonitrile solutions. The PCET* reaction products, the oxidized and deprotonated Ru complex, and the reduced protonated MQ can be distinguished from the excited state electron transfer (ET*) and the excited state proton transfer (PT*) products by the difference in the visible absorption spectrum of the species emerging from the encounter complex. The observed behavior differs from that of reaction of the MLCT state of [(bpy)Ru(4,4'-dhbpy)] (bpy = 2,2'-bipyridine) with MQ, where initial ET* is followed by diffusion-limited proton transfer from the coordinated 4,4'-dhbpy to MQ.

Platinum@Hexaniobate Nanopeapods: A Directed Photocatalytic Architecture for Dye-Sensitized Semiconductor H Production under Visible Light Irradiation.

Platinum@hexaniobate nanopeapods (Pt@HNB NPPs) are a nanocomposite photocatalyst that was selectively engineered to increase the efficiency of hydrogen production from visible light photolysis. Pt@HNB NPPs consist of linear arrays of high surface area Pt nanocubes encapsulated within scrolled sheets of the semiconductor H K NbO and were synthesized in high yield a facile one-pot microwave heating method that is fast, reproducible, and more easily scalable than multi-step approaches required by many other state-of-the-art catalysts. The Pt@HNB NPPs' unique 3D architecture enables physical separation of the Pt catalysts from competing surface reactions, promoting electron efficient delivery to the isolated reduction environment along directed charge transport pathways that kinetically prohibit recombination reactions.

Heterotrimetallic Assemblies with 1,2,4,5-Tetrakis(diphenylphosphino)benzene Bridges: Constructs for Controlling the Separation and Spatial Orientation of Redox-Active Metallodithiolene Groups.

Metallodithiolene complexes of the type [(RCS)M(η-tpbz)] [R = CN, Ph, or -anisyl; M = Ni, Pd, or Pt; tpbz = 1,2,4,5-tetrakis(diphenylphosphino)benzene] chelate transition metals ions to form trimetallic arrays [[(RCS)M(tpbz)]M'], where M' is square planar Pt, tetrahedral Cu, Ag, or Au, or octahedral {ReBr(CO)}/{Re(CO)}. Forcing conditions (190 °C reflux in decalin, 72 h) are demanded for the Re compounds. With third-row metals at the nexus, the compounds are stable to air.

Photocatalytic H-Evolution by Homogeneous Molybdenum Sulfide Clusters Supported by Dithiocarbamate Ligands.

Irradiation at 460 nm of [Mo(μ-S)(μ-S)(SCNR)]I ([]I, R = Me; []I, R = Et; []I, R = Bu; []I, R = CHCH) in a mixed aqueous-polar organic medium with [Ru(bipy)] as photosensitizer and EtN as electron donor leads to H evolution. Maximum activity (300 turnovers, 3 h) is found with R = Bu in 1:9 HO:MeCN; diminished activity is attributed to deterioration of [Ru(bipy)]. Monitoring of the photolysis mixture by mass spectrometry suggests transformation of [Mo(μ-S)(μ-S)(SCNR)] to [Mo(μ-S)(μ-S)(SCNR)] via extrusion of sulfur on a time scale of minutes without accumulation of the intermediate [MoS(SCNR)] or [MoS(SCNR)] species.

Dodecaphenyltetracene.

Dodecaphenyltetracene (4), the largest perphenylacene yet prepared, was synthesized from known tetraphenylfuran, hexaphenylisobenzofuran, and 1,2,4,5-tetrabromo-3,6-diphenylbenzene in three steps. The X-ray structure of the deep red, highly luminescent 4 shows it to be a D -symmetric molecule with an end-to-end twist of 97°. The central acene is encapsulated by the peripheral phenyl substituents, and as a result, the molecule is relatively unreactive and even displays reversible electrochemical oxidation and reduction.

Sterically demanding methoxy and methyl groups in ruthenium complexes lead to enhanced quantum yields for blue light triggered photodissociation.

Ruthenium complexes containing a sterically congested metal center can serve as light activated prodrugs through photo-activated chemotherapy (PACT). In this work, we modified PACT agents containing 6,6'-dihydroxybipyridine (6,6'-dhbp) (Papish et al., Inorg.

Molecular Engineering of Near Infrared Absorbing Thienopyrazine Double Donor Double Acceptor Organic Dyes for Dye-Sensitized Solar Cells.

The thienopyrazine (TPz) building block allows for NIR photon absorption in dye-sensitized solar cells (DSCs) when used as a π-bridge. We synthesized and characterized 7 organic sensitizers employing thienopyrazine (TPz) as a π-bridge in a double donor, double acceptor organic dye design. Donor groups are varied based on electron donating strength and sterics at the donor-π bridge bond with the acceptor groups varied as either carboxylic acids or benzoic acids on the π-bridge.

Expanding the Scope of Ligand Substitution from [M(SCPh] (M = Ni, Pd, Pt) To Afford New Heteroleptic Dithiolene Complexes.

The scope of direct substitution of the dithiolene ligand from [M(SCPh)] [M = Ni (1), Pd (2), Pt (3)] to produce heteroleptic species [M(SCPh)L] (n = 1, 2) has been broadened to include isonitriles and dithiooxamides in addition to phosphines and diimines. Collective observations regarding ligands that cleanly produce [M(SCPh)L], do not react at all, or lead to ill-defined decomposition identify soft σ donors as the ligand type capable of dithiolene substitution. Substitution of MeNC from [Ni(SCPh)(CNMe)] by L provides access to a variety of heteroleptic dithiolene complexes not accessible from 1.

Ruthenium Complexes are pH-Activated Metallo Prodrugs (pHAMPs) with Light-Triggered Selective Toxicity Toward Cancer Cells.

Metallo prodrugs that take advantage of the inherent acidity surrounding cancer cells have yet to be developed. We report a new class of pH-activated metallo prodrugs (pHAMPs) that are activated by light- and pH-triggered ligand dissociation. These ruthenium complexes take advantage of a key characteristic of cancer cells and hypoxic solid tumors (acidity) that can be exploited to lessen the side effects of chemotherapy.

An Overview Of Photosubstitution Reactions Of Ru(II) Imine Complexes And Their Application In Photobiology And Photodynamic Therapy.

This article is a short review that presents a short review of photosubstitution reactions of Ru(II) imine complexes and illustrates their use in the development of therapeutic agents. The review begins with an overview of the photophysical behavior and common photoreactions of Ru(II) imine complexes, with select examples from the literature since the 1960s. It is followed by a more detailed picture of the application of knowledge gained over the years in the development of Ru(II) complexes for photobiology and photodynamic therapy.

A Facile Electrochemical Reduction Method for Improving Photocatalytic Performance of α-FeO Photoanode for Solar Water Splitting.

Electrochemical reduction method is used for the first time to significantly improve the photo-electrochemical performance of α-FeO photoanode prepared on fluorine-doped tin oxide substrates by spin-coating aqueous solution of Fe(NO) followed by thermal annealing in air. Photocurrent density of α-FeO thin film photoanode can be enhanced 25 times by partially reducing the oxide film to form more conductive FeO (magnetite). FeO helps facilitate efficient charge transport and collection from the top α-FeO layer upon light absorption and charge separation to yield enhanced photocurrent density.

Micellar Effects on Photoinduced Electron Transfer in Aqueous Solutions Revisited: Dramatic Enhancement of Cage Escape Yields in Surfactant Ru(II) Diimine Complex/[Ru(NH3)6](2+) Systems.

The effect of cationic micelle incorporation on light induced electron transfer, charge separation and back electron transfer between an aqueous electron donor, [Ru(NH3)6](2+), and a series of Ru(II) diimine complex chromophores/acceptors, is presented. The chromophores have the general formula [(bpy)2Ru(LL)](2+) (LL = bpy; 4-R-4'-methyl-2,2'-bpy, R = pentyl (MC5), terdecyl (MC13), heptadecyl (MC17); 4,4'-di(heptadecyl)-2,2'-bpy (DC17)). Of the five chromophores, the MC13, MC17, and DC17 complexes associate with the added micelle forming surfactant, cetyltrimethylammonium bromide (CTAB).

Correction: Electron transfer rate modulation in a compact Re(i) donor-acceptor complex.

Correction for 'Electron transfer rate modulation in a compact Re(i) donor-acceptor complex' by Yuankai Yue et al., Dalton Trans., 2015, 44, 8609-8616.

Homoleptic Tris-Diphosphine Re(I) and Re(II) Complexes and Re(II) Photophysics and Photochemistry.

The ligand-to-metal charge transfer state (LMCT) of [(dmpe)3Re](2+) (dmpe = 1,2-bis(dimethylphosphino)ethane) has been demonstrated to be a potent oxidant (E(0)(Re(2+*)/Re(+)) = 2.61 V vs standard calomel electrode). This complex has been traditionally prepared by nontrivial routes in low yields, and very little has been achieved in optimizing the ground state and emission energy properties of the general class of complexes [(PP)3Re](2+) (PP = chelating diphosphine) through phosphine modification.

Electron transfer rate modulation in a compact Re(I) donor-acceptor complex.

Formation of the charge transfer state with the rate constant of (10 ps)(-1) has recently been reported for the complex fac-[Re(I)(CO)3(DCEB)(3DMABN)] (ReEBA); where 3DMABN is 3-dimethylaminobenzonitrile, serving as an electron donor, and DCEB is 4,4'-(dicarboxyethyl)-2,2-bipyridine, serving as an electron acceptor (Y. Yue et al., J.

Host-guest interactions derived multilayer perylene diimide thin film constructed on a scaffolding porphyrin monolayer.

The development of methods to grow well-ordered chromophore thin films on solid substrates is of importance because such surface-associated arrays have potential applications in the generation of functional electronic and optical materials and devices. In this article, we demonstrate a straightforward layer-by-layer (LBL) supramolecular deposition strategy to prepare numerous layers (up to 19) of functionalized perylene diimide (PDI) chromophores built upon a covalent scaffolding multivalent porphyrin monolayer. Our thin film formation strategy employs water as the immersion solvent and exploits the β-cyclodextrin-adamantane host-guest couple in addition to PDI based aromatic stacking.

Following Oxygen Consumption in Singlet Oxygen Reactions via Changes in Sensitizer Phosphorescence.

This work reports an examination of singlet oxygen reactions with amino acid substrates by a method involving measurement of the change in phosphorescence intensity of the singlet oxygen sensitizer. The sensitizer, a Ru(II) bipyridyl complex covalently linked to pyrene, has long-lived phosphorescence in N2 purged aqueous solutions (τ0 ~ 20 μs) that is nearly completely quenched by oxygen in aerated solutions. Irradiation of the complex in water containing sub mM concentrations of histidine, tryptophan and methionine results in a dramatic, easily visible increase in the phosphorescence intensity over a period of 10-100 s.

Sn(IV) Schiff base complexes: triplet photosensitizers for photoredox reactions.

We present the synthesis and characterization of a series of four fluorescent Sn(iv) Schiff base complexes, which also possess long-lived triplet excited states. The complexes absorb visible light (λmax = 420 to 462 nm) and the optical properties are easily tunable without laborious synthetic elaboration. The triplet excited states are not luminescent, but can be observed and followed using nanosecond transient absorption spectroscopy.

Full-electron ligand-to-ligand charge transfer in a compact Re(I) complex.

Ligand-to-ligand charge transfer (LLCT) states in transition metal complexes are often characterized by fractional electron transfer due to coupling of the LLCT state with many other states via the metal. We designed and characterized a compact Re(I) complex that displays essentially full-electron charge transfer in the LLCT excited state. The complex, [Re(DCEB)(CO)3(L)](+) (DCEB = 4,4'-dicarboxyethyl-2,2'-bipyridine), referred to as ReEBA, features two redox active ligands with strong electron accepting (DCEB) and electron donating (L is 3-dimethylaminobenzonitrile (3DMABN)) properties.

Photochemical generation of strong one-electron reductants via light-induced electron transfer with reversible donors followed by cross reaction with sacrificial donors.

This work illustrates a modified approach for employing photoinduced electron transfer reactions coupled to secondary irreversible electron transfer processes for the generation of strongly reducing equivalents in solution. Through irradiation of [Ru(LL)3](2+) (LL= diimine ligands) with tritolylamine (TTA) as quencher and various alkyl amines as sacrificial electron donors, yields in excess of 50% can be achieved for generation of reductants with E(0)(2+/1+) values between -1.0 and -1.

Water-soluble porphyrin nanospheres: enhanced photo-physical properties achieved via cyclodextrin driven double self-inclusion.

We describe a method to construct water-soluble porphyrinic nanospheres with enhanced photo-physical properties as a result of precluding (via intra-molecular host-guest interactions) the individual porphyrins units from aromatic-aromatic stacking.

Evaluating the extent of intramolecular charge transfer in the excited states of rhenium(I) donor-acceptor complexes with time-resolved vibrational spectroscopy.

Excited states in transition-metal complexes, even in those featuring ligands with strong electron donating and accepting properties, often involve only partial charge transfer between the donor and acceptor ligands. The excited-state properties of [Re(bpy)(CO)3L](+) compounds were studied, where L is 4-dimethylaminobenzonitrile (Re4DMABN), 3-dimethylaminobenzonitrile (Re3DMABN), and benzonitrile (ReBN) using time-resolved infrared (TRIR) and electronic spectroscopy methods as well as electronic structure computations. The DMABN complexes exhibit strongly solvent-dependent luminescence; the excited state lifetime decreases from microseconds in dichloromethane to several nanoseconds in mixed MeOH:DCM (1:1) solvent.