Doping Effects in Cluster‐Mediated Bond Activation

Gas‐phase investigations of judiciously doped oxide clusters permit to address fundamental challenges related to, for example, the low‐temperature oxidation of CO or the selective conversion of hydrocarbons. Modifying the size and composition of a free cluster in a controlled way enables the modification of local charge effects and of spin states, and spectroscopic studies in combination with computational work help to identify the active site of a catalyst and to unravel mechanistic details. Also, the interplay of the support material with the reactive part of a composite catalyst cluster can be addressed. Examples will be presented demonstrating how and why the gas‐phase reactivities of heteronuclear clusters, in comparison with their homonuclear counterparts, toward small, generally rather inert molecules can be increased, decreased, or not significantly affected.     

Sol Processing of Conjugated Carbon Nitride Powders for Thin‐Film Fabrication

The chemical protonation of graphitic carbon nitride (CN) solids with strong oxidizing acids, for example HNO₃, is demonstrated as an efficient pathway for the sol processing of a stable CN colloidal suspension, which can be translated into thin films by dip/disperse‐coating techniques. The unique features of CN colloids, such as the polymeric matrix and the reversible hydrogen bonding, result in the thin‐film electrodes derived from the sol solution exhibiting a high mechanical stability with improved conductivity for charge transport, and thus show a remarkably enhanced photo‐electrochemical performance. The polymer system can in principle be broadly tuned by hybridization with desired functionalities, thus paving the way for the application of CN for specific tasks, as exemplified here by coupling with carbon nanotubes.     

Two‐Photon Voltmeter for Measuring a Molecular Electric Field

We present a new approach for determining the strength of the dipolar solute‐induced reaction field, along with the ground‐ and excited‐state electrostatic dipole moments and polarizability of a solvated chromophore, using exclusively one‐photon and two‐photon absorption measurements. We verify the approach on two benchmark chromophores N,N‐dimethyl‐6‐propionyl‐2‐naphthylamine (prodan) and coumarin 153 (C153) in a series of toluene/dimethyl sulfoxide (DMSO) mixtures and find that the experimental values show good quantitative agreement with literature and our quantum‐chemical calculations. Our results indicate that the reaction field varies in a surprisingly broad range, 0–10⁷ V cm^?1, and that at close proximity, on the order of the chromophore radius, the effective dielectric constant of the solute–solvent system displays a unique functional dependence on the bulk dielectric constant, offering new insight into the close‐range molecular interaction.     

Directed meta‐Selective Bromination of Arenes with Ruthenium Catalysts

A Ru‐catalyzed direct C? H activation/meta‐bromination of arenes bearing pyridyl, pyrimidyl, and pyrazolyl directing groups has been developed. A series of bromo aryl pyridines and pyrimidines have been synthesized, and further coupling reactions have also been demonstrated for a number of representative functionalized arenes. Preliminary mechanistic studies have revealed that this reaction may proceed through radical‐mediated bromination when NBS is utilized as the bromine source. This type of transformation has opened up a new direction for the radical non‐ipso functionalization of metal with regard to future C? H activation development that would allow the remote functionalization of aromatic systems.     

π‐Expanded α,β‐Unsaturated Ketones: Synthesis,Optical Properties,and Two‐Photon‐Induced Polymerization

A library of π‐expanded α,β‐unsaturated ketones was designed and synthesized. They were prepared by a combination of Wittig reaction, Sonogashira reaction, and aldol condensation. It was further demonstrated that the double aldol condensation can be performed effectively for highly polarized styrene‐ and diphenylacetylene‐derived aldehydes. The strategic placement of two dialkylamino groups at the periphery of D ‐π‐A‐π‐D molecules resulted in dyes with excellent solubility. These ketones absorb light in the region 400–550 nm. Many of them display strong solvatochromism so that the emission ranges from 530–580 nm in toluene to the near‐IR region in benzonitrile. Ketones based on cyclobutanone as central moieties display very high fluorescence quantum yields in nonpolar solvents, which decrease drastically in polar media. Photophysical studies of these new functional dyes revealed that they possess an enhanced two‐photon absorption cross section when compared with simpler ketone derivatives. Due to strong polarization of the resulting dyes, values of two‐photon absorption cross sections on the level of 200–300 GM at 800 nm were achieved, and thanks to that as well as the presence of the keto group, these new two‐photon initiators display excellent performance so that the operating region is 5–75 mW in some cases.     

Differentiation between Shallow and Deep Charge Trap States on Single Poly(3‐hexylthiophene) Chains through Fluorescence Photon Statistics

Blinking of the photoluminescence (PL) emitted from individual conjugated polymer chains is one of the central observations made by single‐molecule spectroscopy (SMS). Important information, for example regarding excitation energy transfer, can be extracted by evaluating dynamic quenching. However, the nature of trap states, which are responsible for PL quenching, often remains obscured. We present a detailed investigation of the photon statistics of single poly(3‐hexylthiophene) (P3HT) chains obtained by SMS. The photon statistics provide a measure of the number and brightness of independently emitting areas on a single chain. These observables can be followed during blinking. A decrease in PL intensity is shown to be correlated with either 1) a decrease in the average brightness of the emitting sites; or 2) a decrease in the number of emitting regions. We attribute these phenomena to the formation of 1) shallow charge traps, which can weakly affect all emitting areas of a single chain at once; and 2) deep traps, which have a strong effect on small regions within the single chains.     

Diketopyrrolopyrrole‐Porphyrin Conjugates with High Two‐Photon Absorption and Singlet Oxygen Generation for Two‐Photon Photodynamic Therapy

Two‐photon photodynamic therapy is a promising therapeutic method which requires the development of sensitizers with efficient two‐photon absorption and singlet‐oxygen generation. Reported here are two new diketopyrrolopyrrole‐porphyrin conjugates as robust two‐photon absorbing dyes with high two‐photon absorption cross‐sections within the therapeutic window. Furthermore, for the first time the singlet‐oxygen generation efficiency of diketopyrrolopyrrole‐containing systems is investigated. A preliminary study on cell culture showed efficient two‐photon induced phototoxicity.     

Column preconcentration and electrothermal atomic absorption spectrometric determination of rhodium in some food and standard samples

In the present work, an electrothermal atomic absorption spectrometric method has been developed for the determination of ultra‐trace amounts of rhodium after adsorption of its 2‐(5‐bromo‐2‐pyridylazo)‐5‐diethylaminophenol/tetraphenylborate ion associated complex at the surface of alumina. Several factors affecting the extraction efficiency such as the pH, type of eluent, sample and eluent flow rates, sorption capacity of alumina and sample volume were investigated and optimized. The relative standard deviation for eight measurements of 0.1 ng/mL of rhodium was ±6.3%. In this method, the detection limit was 0.003 ng/mL in the original solution. The sorption capacity of alumina and the linear range for Rh(III) were evaluated as 0.8 mg/g and 0.015–0.45 ng/mL in the original solution, respectively. The proposed method was successfully applied for the extraction and determination of rhodium content in some food and standard samples with high recovery values.