Quenching of Photoluminescence in ZnO QDs Decorating Multiwalled Carbon Nanotubes

We report the controlled growth of ZnO quantum dots (QDs) on the sidewalls of multiwalled carbon nanotubes (MWCNTs) by a one‐step process and study the effect on the photoluminescence (PL) properties of the ZnO QDs‐MWCNT composite. The PL intensity of the composite is quenched and the lifetime is reduced compared to the only ZnO QDs. The origin of the PL quenching is discussed in terms of energy transfer, which is examined by varying the density and size of ZnO QDs by changing the molar concentration of the precursor solution for ZnO and the amount of MWCNT.     

Characterisation of Nanohybrids of Porphyrins with Metallic and Semiconducting Carbon Nanotubes by EPR and Optical Spectroscopy

Single‐walled carbon nanotubes (SWCNTs) are noncovalently functionalised with octaethylporphyrins (OEPs) and the resulting nanohybrids are isolated from the free OEPs. Electron paramagnetic resonance (EPR) spectroscopy of cobalt(II)OEP, adsorbed on the nanotube walls by π–π‐stacking, demonstrates that the CNTs act as electron acceptors. EPR is shown to be very effective in resolving the different interactions for metallic and semiconducting tubes. Moreover, molecular oxygen is shown to bind selectively to nanohybrids with semiconducting tubes. Water solubilisation of the porphyrin/CNT nanohybrids using bile salts, after applying a thorough washing procedure, yields solutions in which at least 99 % of the porphyrins are interacting with the CNTs. Due to this purification, we observe, for the first time, the isolated absorption spectrum of the interacting porphyrins, which is strongly red‐shifted compared to the free porphyrin absorption. In addition a quasi‐complete quenching of the porphyrin fluorescence is also observed.     

ZnO‐Coated Carbon Nanotubes: Inter‐Diffusion of Carboxyl Groups and Enhanced Photocurrent Generation

ZnO is a defect‐governed oxide and emits light at both visible and UV regimes. This work employs atomic layer deposition to produce oxide particles on oxygenated carbon nanotubes, and the composites only show emission profiles at short wavelengths. The quenching of defect‐related emissions at long wavelengths is verified, owing to carboxyl diffusion into oxygen vacancies, and doping is supported by ZnCO₃ formation in oxide lattice. Fully coated tubes display an increased photocurrent and the quantum efficiency increases by 22 % relative to the bare nanotubes.     

DNA‐Directed Attachment of Carbon Nanotubes for Enhanced Label‐Free Electrochemical Detection of DNA Hybridization

Multi‐walled carbon nanotubes (MWNTs) were used as nanowires, which combined DNA molecules to a carbon paste electrode (CPE). The attachment of MWNT on the electrode surface was controlled by a hybridization assay between adenine and thymine containing oligonucleotides. The appearance of guanine oxidation signal after hybridization with target DNA greatly simplified the specific sequence DNA detection mechanism. Combination of sidewall‐ and end‐functionalization of MWNT provided a significant enhancement in the voltammetric signal of guanine oxidation in comparison with the signals obtained from only end‐oxidized MWNT modified CPE and a bare CPE. A control experiment involving adenine containing polynucleotide (poly(A)) instead of adenine probe modified MWNT was performed. The effect of target and noncomplementary DNA concentration on the guanine signal was also monitored. Discrimination against single‐base mismatch and noncomplementary DNA was achieved by surfactant containing washing solution. The promising conductivity of carbon nanotubes, and the creation of a larger surface area for DNA immobilization by sidewall‐ and end‐oxidation of MWNT provided a detection limit down to 10 pg/mL, which is compatible with the demand of the genetic tests.     

Explosive Decomposition of a Melamine–Cyanuric Acid Supramolecular Assembly for Fabricating Defect‐Rich Nitrogen‐Doped Carbon Nanotubes with Significantly Promoted Catalysis

A facile and scalable approach for fabricating structural defect‐rich nitrogen‐doped carbon nanotubes (MCSA‐CNTs) through explosive decomposition of melamine–cyanuric acid supramolecular assembly is presented. In comparison to pristine carbon nanotubes, MCSA‐CNT exhibits significantly enhanced catalytic performance in oxidant‐ and steam‐free direct dehydrogenation of ethylbenzene, demonstrating the potential for metal‐free clean and energy‐saving styrene production. This finding also opens a new horizon for preparing highly‐efficient carbocatalysts rich in structural defect sites for diverse transformations.     

Highly Efficient Low‐Temperature Plasma‐Assisted Modification of TiO2 Nanosheets with Exposed {001} Facets for Enhanced Visible‐Light Photocatalytic Activity

Anatase TiO₂ nanosheets with exposed {001} facets have been controllably modified under non‐thermal dielectric barrier discharge (DBD) plasma with various working gas, including Ar, H₂, and NH₃. The obtained TiO₂ nanosheets possess a unique crystalline core/amorphous shell structure (TiO₂@TiO_2?x), which exhibit the improved visible and near‐infrared light absorption. The types of dopants (oxygen vacancy/surface Ti³⁺/substituted N) in oxygen‐deficient TiO₂ can be tuned by controlling the working gases during plasma discharge. Both surface Ti³⁺ and substituted N were doped into the lattice of TiO₂ through NH₃ plasma discharge, whereas the oxygen vacancy or Ti³⁺ (along with the oxygen vacancy) was obtained after Ar or H₂ plasma treatment. The TiO₂@TiO_2?x from NH₃ plasma with a green color shows the highest photocatalytic activity under visible‐light irradiation compared with the products from Ar plasma or H₂ plasma due to the synergistic effect of reduction and simultaneous nitridation in the NH₃ plasma.     

Energy‐Funneling‐Based Broadband Visible‐Light‐Absorbing Bodipy–C60 Triads and Tetrads as Dual Functional Heavy‐Atom‐Free Organic Triplet Photosensitizers for Photocatalytic Organic Reactions

C₆₀–bodipy triads and tetrads based on the energy‐funneling effect that show broadband absorption in the visible region have been prepared as novel triplet photosensitizers. The new photosensitizers contain two or three different light‐harvesting antennae associated with different absorption wavelengths, resulting in a broad absorption band (450–650 nm). The panchromatic excitation energy harvested by the bodipy moieties is funneled into a spin converter (C₆₀), thus ensuring intersystem crossing and population of the triplet state. Nanosecond time‐resolved transient absorption and spin density analysis indicated that the T₁ state is localized on either C₆₀ or the antennae, depending on the T₁ energy levels of the two entities. The antenna‐localized T₁ state shows a longer lifetime (τ_T=132.9 μs) than the C₆₀‐localized T₁ state (ca. 27.4 μs). We found that the C₆₀ triads and tetrads can be used as dual functional photocatalysts, that is, singlet oxygen (¹O₂) and superoxide radical anion (O₂ ^{. ?}) photosensitizers. In the photooxidation of naphthol to juglone, the ¹O₂ photosensitizing ability of the C₆₀ triad is a factor of 8.9 greater than the conventional triplet photosensitizers tetraphenylporphyrin and methylene blue. The C₆₀ dyads and triads were also used as photocatalysts for O₂ ^{. ?}‐mediated aerobic oxidation of aromatic boronic acids to produce phenols. The reaction times were greatly reduced compared with when [Ru(bpy)₃Cl₂] was used as photocatalyst. Our study of triplet photosensitizers has shown that broadband absorption in the visible spectral region and long‐lived triplet excited states can be useful for the design of new heavy‐atom‐free organic triplet photosensitizers and for the application of these triplet photosensitizers in photo‐organocatalysis.     

Visible‐Light‐Responsive Reversible Photoacid Based on a Metastable Carbanion

A new photoacid that reversibly changes from a weak to a strong acid under visible light was designed and synthesized. Irradiation generated a metastable state with high C?H acidity due to high stability of a trifluoromethyl‐phenyl‐tricyano‐furan (CF₃PhTCF) carbanion. This long‐lived metastable state allows a large proton concentration to be reversibly produced with moderate light intensity. Reversible pH change of about one unit was demonstrated by using a 0.1 mM solution of the photoacid in 95 % ethanol. The quantum yield was calculated to be as high as 0.24. Kinetics of the reverse process can be fitted well to a second‐order‐rate equation with k=9.78×10² M ^?1 s^?1. Response to visible light, high quantum yield, good reversibility, large photoinduced proton concentration under moderate light intensity, and good compatibility with organic media make this photoacid a promising material for macroscopic control of proton‐transfer processes in organic systems.     

Multiple Decay Mechanisms and 2D‐UV Spectroscopic Fingerprints of Singlet Excited Solvated Adenine‐Uracil Monophosphate

The decay channels of singlet excited adenine uracil monophosphate (ApU) in water are studied with CASPT2//CASSCF:MM potential energy calculations and simulation of the 2D‐UV spectroscopic fingerprints with the aim of elucidating the role of the different electronic states of the stacked conformer in the excited state dynamics. The adenine ¹L_a state can decay without a barrier to a conical intersection with the ground state. In contrast, the adenine ¹L_b and uracil S(U) states have minima that are separated from the intersections by sizeable barriers. Depending on the backbone conformation, the CT state can undergo inter‐base hydrogen transfer and decay to the ground state through a conical intersection, or it can yield a long‐lived minimum stabilized by a hydrogen bond between the two ribose rings. This suggests that the ¹L_b, S(U) and CT states of the stacked conformer may all contribute to the experimental lifetimes of 18 and 240 ps. We have also simulated the time evolution of the 2D‐UV spectra and provide the specific fingerprint of each species in a recommended probe window between 25 000 and 38 000 cm^?1 in which decongested, clearly distinguishable spectra can be obtained. This is expected to allow the mechanistic scenarios to be discerned in the near future with the help of the corresponding experiments. Our results reveal the complexity of the photophysics of the relatively small ApU system, and the potential of 2D‐UV spectroscopy to disentangle the photophysics of multichromophoric systems.     

Cs4K2CuSi2O8: Synthese,Kristallstruktur, UV‐Vis‐IR‐Daten

Cs₄K₂CuSi₂O₈: Synthesis, Crystal Structure, UV‐Vis‐IR Data Cs₄K₂CuSi₂O₈ may be obtained via a redox reaction of KCuO₂ in the presence of Cs₂O and SiO₂ with the container material (Cu) at 450 °C as blue single crystals which are sensitive to moisture. Powder samples were obtained by annealing intimate mixtures of the binary oxides under an inert gas atmosphere (Ar) in sealed Ag containers at 500 °C. The crystal structure contains isolated trimeric anions of [O₂SiO₂CuO₂SiO₂]^6–. Cu²⁺ in square‐planar coordination share trans‐edges with [SiO₄] tetrahedra. Spectroscopic investigations focus on the bonding situation of the [CuO₄] unit (AOM) and characteristic vibrational modes of the silicate.     

Spectroscopic Characteristics of Differently Produced Single‐Walled Carbon Nanotubes

Single‐walled carbon nanotubes (SWNTs) synthesized with different methods are investigated by using multiple characterization techniques, including Raman scattering, optical absorption, and X‐ray absorption near edge structure, along with X‐ray photoemission by following the total valence bands and C 1s core‐level spectra. Four different SWNT materials (produced by arc discharge, HiPco, laser ablation, and CoMoCat methods) contain nanotubes with diameters ranging from 0.7 to 2.8 nm. The diameter distribution and the composition of metallic and semiconducting tubes of the SWNT materials are strongly affected by the synthesis method. Similar sp² hybridization of carbon in the oxygenated SWNT structure can be found, but different surface functionalities are introduced while the tubes are processed. All the SWNTs demonstrate stronger plasmon resonance excitations and lower electron binding energy than graphite and multiwalled carbon nanotubes. These SWNT materials also exhibit different valence‐band X‐ray photoemission features, which are considerably affected by the nanotube diameter distribution and metallic/semiconducting composition.     

Covalent incorporation of methyl red dyes into double-stranded DNA for their ordered clustering

An ordered dye cluster of Methyl Reds was formed in double-stranded DNA by hybridizing two complementary DNA-dye conjugates, each involving a Methyl Red moiety on a threoninol linker and a 1,3-propanediol spacer arranged alternately in the middle of the DNA sequence. In the duplex, Methyl Reds from each strand were axially stacked antiparallel to each other, as determined from NMR analysis. This clustering of Methyl Reds induced distinct changes in both UV/Vis and CD spectra. Single-stranded DNA-Methyl Red conjugates on D-threoninol linkers and (1,3-propanediol) spacers exhibited broad absorption spectra with lambda(max) at around 480 nm, and almost no CD was observed at around the absorption maximum of Methyl Red. However, as Methyl Reds were clustered by hybridization, lambda(max) shifted towards shorter wavelengths with respect to its monomeric transition. This hypsochromic shift increased as the number of Methyl Red molecules increased. Furthermore, a positive couplet was also strongly induced here. These dye clusters are H-aggregates, in which molecular excitons are coupled. The positive couplet demonstrates that the clusters on D-threoninol form a right-handed helix. In contrast, the induced CD became much weaker with Methyl Red on L-threoninol, which intrinsically prefers counterclockwise winding. Thus, mutual orientation of the stacked dye molecules was controlled by the chirality of the linker.     

α‐Chymotrypsin‐Catalyzed Reaction Confined in Block‐Copolymer Vesicles

Herein the reactivity of the enzyme α‐chymotrypsin in the confinement of polystyrene‐block‐poly(acrylic acid) (PS‐b‐PAA) vesicles was investigated. Enzyme and substrate molecules were encapsulated in PS‐b‐PAA vesicles with internal diameters ranging from 26 nm to 165 nm during the formation of the vesicles. While the loading efficiencies of enzyme and substrate molecules were practically identical for vesicles of identical size, they were found to increase with decreasing vesicle size. The kinetics of the α‐chymotrypsin catalyzed hydrolysis of N‐succinyl‐Ala‐Ala‐Phe‐7‐amido‐4‐methylcoumarin (AMC) was evaluated following the increase of the absorption of the product 7‐amino‐4‐methylcoumarin by UV/Vis spectroscopy. The values of the catalytic turnover number obtained for reactions inside vesicles with different sizes showed an increase of up to fourteen times compared to the bulk value with decreasing vesicle volume, while the values of the Michaelis–Menten constant decreased, respectively. This increase in reactivity of α‐chymotrypsin is attributed to the effect of vesicle–wall interactions in the finite encapsulated space, where the reagents could diffuse, leading to enhanced collision frequencies.     

Near‐Infrared Emission Quantum Yield of Soluble Short Single‐Walled Carbon Nanotubes

Soluble short single‐walled carbon nanotubes in aerated D₂O emit in the near‐infrared (NIR) region (see picture) with a quantum yield of (3.9±0.5) ×10^?3 and a half‐life of 7.65 μs. This emission is quenched by electron‐ acceptor molecules.

     

Spatially Controllable DNA Condensation by a Water‐Soluble Supramolecular Hybrid of Single‐Walled Carbon Nanotubes and β‐Cyclodextrin‐Tethered Ruthenium Complexes

A supramolecular hybrid is prepared by the supramolecular surface modification of single‐walled carbon nanotube (SWCNT) with cationic β‐cyclodextrin‐tethered ruthenium complexes through a spacer molecule that contains both an adamantane and a pyrene moiety. By employing the supramolecular hybrid, spatially controllable DNA condensation along the SWCNT skeleton is achieved by anchoring cationic ruthenium complexes on the surface. Furthermore, because of the unique physiological properties of SWCNTs, the cationic supramolecular hybrid can be used as a nonviral gene delivery system with the ruthenium complexes as a fluorescent probe to monitor uptake of DNA by cells.     

Synthesis and Characterization of 6,13‐Diamino‐Substituted Pentacenes

A series of 6,13‐diamino‐substituted pentacenes 1 a – d has been prepared and characterized as a new class of pentacene derivatives with strong donor ability and enhanced solubility in common organic solvents. The spectroelectrochemical and DFT studies revealed that the two‐electron oxidation process was accompanied by the substantial structural change into a butterfly‐like conformation of the pentacene moiety. More importantly, the extent of deformation from the planar pentacene moiety in the dications of 6,13‐diaminopentacene is tunable by varying the N‐substituents.