Photocatalytic Atom Transfer Radical Addition to Olefins Utilizing Novel Photocatalysts.

Photocatalysis is a rapidly evolving area of research in modern organic synthesis. Among the traditional photocatalysts, metal-complexes based on ruthenium or iridium are the most common. Herein, we present the synthesis of two photoactive, ruthenium-based complexes bearing pyridine-quinoline or terpyridine ligands with extended aromatic conjugation. Our complexes were utilized in the atom transfer radical addition (ATRA) of haloalkanes to olefins, using bromoacetonitrile or bromotrichloromethane as the source of the alkyl group. The tailor-made ruthenium-based catalyst bearing the pyridine-quinoline bidentate ligand proved to be the best-performing photocatalyst, among a range of metal complexes and organocatalysts, efficiently catalyzing both reactions. These photocatalytic atom transfer protocols can be expanded into a broad scope of olefins. In both protocols, the photocatalytic reactions led to products in good to excellent isolated yields.

A Squaraine Derivative for Cost-Effective, Quick, and Highly Sensitive Determination of Mercury and Thiols and pH Sensing.

The introduction of innovative sensing approaches is of increasing interest in the development of analytical platforms and methodologies for the colorimetric, fluorimetric, and/or optical detection of important analytes. Herein, the synthesis of a novel squaraine derivative is reported, as well as its successful utilization in the colorimetric and fluorimetric determination of thiols. The reported squaraine was also evaluated as a pH sensor. In addition, a promising paper-based colorimetric method for mercury detection was developed and evaluated.

Co-adsorbents: a key component in efficient and robust dye-sensitized solar cells.

Since the establishment of dye-sensitized solar cells in the early '90s, both the efficiency and stability of these third generation photovoltaics have been greatly enhanced. Nevertheless, there still exist many unwanted processes that impede operation of dye-sensitized solar cells, encumbering the achievement of the maximum theoretical power conversion efficiency and decreasing the devices' long-term operation. These processes include charge recombination, dye aggregation, dye desorption, and high protonation degrees of the semiconductor's surface. This Minireview focuses on a powerful strategy developed to address these problems, namely the use of co-adsorbents. All types of co-adsorbents utilized thus far are categorized in terms of the chemical identity of their anchoring group; in addition their operational mechanisms are presented and the properties that a functional molecule should possess to be applied as an efficient co-adsorbent are discussed.

A Family of Potent Ru(II) Photosensitizers with Enhanced DNA Intercalation: Bimodal Photokillers.

A new family of Ru(II)-based photosensitizers was synthesized and systematically characterized. The ligands employed to coordinate the ruthenium metal center were the commercially available 2,2'-bipyridine and a pyridine-quinoline hybrid bearing an anthracene moiety. The complexes obtained carry either PF6- or Cl(-) counterions. These counterions determine the complexes' hydrophobic or hydrophilic character, respectively, therefore dictating their solubility in biologically related media. All photosensitizers exhibit characteristic, relatively strong and wide UV-Vis absorption spectral profiles. Their high efficiency in generating cytotoxic singlet oxygen was established (up to ΦΔ ~0.8). Moreover, the interaction of these photosensitizers with double-stranded DNA was studied fluoro- and photospectroscopically and their binding affinities were found to be of the order of 3 × 10(7)  M(-1) . All complexes are photocytotoxic to DU145 human prostate cancer cells. The highest light-induced toxicity was conferred by the photosensitizers bearing Cl(-) counterions, probably due to the looser ionic "chaperoning" of Cl(-) , in comparison to PF6-, leading to higher cell internalization.

Novel Ru(II) sensitizers bearing an unsymmetrical pyridine-quinoline hybrid ligand with extended π-conjugation: synthesis and application in dye-sensitized solar cells.

Heteroleptic ruthenium(II) sensitizers DV42 and DV51, encompassing a novel unsymmetrical pyridine-quinoline hybrid ligand with extended π-conjugation, were synthesized, characterized, and utilized in nanocrystalline dye-sensitized solar cells. Due to the extended conjugation of DV42 and DV51, the absorption of the corresponding sensitized TiO2 films extends into the red spectral range, shifted by 30-40 nm relative to the absorption of TiO2 films sensitized with the standard Z907 ruthenium(II) dye. Contact angle measurements of DV42- and DV51-sensitized TiO2 films suggest that these films are hydrophilic with contact angle values commonly observed upon sensitization with the standard N3 ruthenium(II) dye. Electrochemical studies of the novel ruthenium(II) dyes show that their first oxidation potentials lie well below the I(-)/I3(-) redox potential allowing easy regeneration. The excited-state oxidation potentials of both dyes lie above the TiO2 conduction band, permitting efficient electron injection from the excited dye molecules into the semiconductor conduction band. Liquid electrolyte dye-sensitized solar cells incorporating DV42- or DV51-sensitized TiO2 photoelectrodes afford overall power conversion efficiencies of 3.24 or 4.36% respectively. These efficiencies are up to 56% of the power conversion efficiencies attained by TiO2 photoelectrodes sensitized by the benchmark Z907 ruthenium(II) dye under similar experimental conditions.