Search results for "Single"
showing 10 items of 4920 documents
Inside Cover: An Unusually Small Singlet-Triplet Gap in a Quinoidal 1,6-Methano[10]annulene Resulting from Baird’s 4nπ-Electron Triplet Stabilization…
2015
Performance of interdigitated nanoelectrodes for electrochemical DNA biosensor.
2003
An electrochemical methodology for bio-molecule sensing using an array of well-defined nanostructures is presented. We describe the fabrication by e-beam lithography of nanoelectrodes consisting of a 100 micro m x 50 micro m area containing interdigitated electrodes of 100 nm in width and interelectrode distance of 200 nm. Sensitivity and response time of the nanoelectrodes are compared to the responses of macro- and microelectrodes. The specificity of the sensor is studied by modifying the gold electrodes with DNA. The technique enables to characterize both single and double-stranded DNA of 15 nucleotides. A special electrochemical cell is adapted to control the temperature and measure the…
Diffusion Control in Single-Site Zinc Reticular Amination Catalysts.
2020
Zn-containing metal-organic frameworks have been used for the first time as heterogeneous catalysts in the amination of C-Cl bonds. The use of extended bis(pyrazolate) linkers can generate highly porous architectures, which favor the diffusion of amines to the confined spaces with respect to other imidazolate frameworks with narrower pore windows. The N4Zn nodes of the Zn-reticular framework show comparable activity to state-of-the-art homogeneous Zn amination catalysts, avoiding the use of basic conditions, precious metals, or other additives. This is combined with long-term activity and stability upon several reaction cycles, without contamination of the reaction product. ispartof: INORGA…
On the electronic structure of a dianion, a radical anion, and a neutral biradical (HB)11CCCC(BH)11 carborane dimer
2009
Abstract The electronic structure of a neutral, a radical anion, and a dianion carborane dimer connected via an acetylenic bridge unit (HB) 11 C C C C(BH) 11 is analyzed by quantum chemical methods. Geometries, relative stabilities, and singlet–triplet gaps are determined in the neutral and dianion species for the lowest-lying singlet and triplet states and for the doublet ground state in the radical anion. As for the recently studied biradical compounds derived from o -carborane, m -carborane and p -carborane [J. Chem. Theory Comput. 4 (2008) 1338] via double hydrogen abstraction, the neutral dimeric compound displays a biradical ground-state structure in which both singlet and triplet sta…
Molecule Isomerism Modulates the Diradical Properties of Stable Singlet Diradicaloids
2019
Inclusion of quinoidal cores in conjugated hydrocarbons is a common strategy to modulate the properties of diradicaloids formed by aromaticity recovery within the quinoidal unit. Here we describe an alternative approach of tuning of diradical properties in indenoindenodibenzothiophenes upon anti → syn isomerism of the benzothiophene motif. This alters the relationship of the S atom with the radical center from linear to cross conjugation yet retains the same 2,6-naphtho conjugation pattern of the rearomatized core. We conduct a full comparison between the anti and syn derivatives based on structural, spectroscopic, theoretical, and magnetic measurements, showing that these systems are stabl…
Electron Energy Loss and DFT/SCI Study of the Singlet and Triplet Excited States of Aminobenzonitriles and Benzoquinuclidines: Role of the Amino Gro…
1999
Spectroscopic consequences of varying the twist angle of the amino group in aminobenzonitrile systems in the electronic ground state are investigated by applying electron energy loss (EEL) spectroscopy and density functional theory to 4-N,N-dimethylaminobenzonitrile (DMABN), 4-N,N-dimethylamino-3,5-dimethylbenzonitrile (MMD), benzoquinuclidine (BQ), and 6-cyanobenzoquinuclidine (CBQ). A number of singlet and triplet excited states was observed and assigned with the help of DFT/SCI theory. The results characterize the gas-phase spectroscopy of the molecules and verify to within 0.3 eV the predictive power of DFT/SCI theory for vertical states over a wide range of twist and pyramidalization a…
Ultraviolet luminescence of ScPO4, AlPO4 and GaPO4 crystals.
2013
The luminescence of self-trapped excitons (STEs) was previously observed and described for the case of tetragonal-symmetry ScPO4 single crystals. The subject band in this material is situated in the UV spectral range of ?210?nm or ?5.8?eV. In the present work, we are both expanding this earlier luminescence study and seeking to identify similar luminescence phenomena in other orthophosphate crystals, i.e., AlPO4 and GaPO4. These efforts have proven to be successful?in spite of the structural differences between these materials and ScPO4. Specifically we have found that for AlPO4 and GaPO4, in addition to an ?-quartz-like STE, there is a UV luminescence band that is similar in position and d…
Electro-optical and laser spectrofluorimetry study of coumarins 7 and 30: evidence for the existence of the close-lying electronic states and conform…
1997
Our experiments and calculations reveal a set of anomalous and interesting properties of coumarin 7 (CU7) and coumarin 30 (CU30) in solution. The spectral dependence of electro-optical coefficients and, consequently, dipole moments indicates that the absorption band is a superposition of several (at least two) electronic transitions. Probably, there are two close-lying π,π* singlet electronic excited states which contribute to the first absorption band. The calculations using the MM2 program show that both dyes in the ground state have two stable plane anti conformers. From time-resolved spectrofluorimetric measurements we obtained evidence for the existence of conformers in paraffin oil so…
Innentitelbild: An Unusually Small Singlet-Triplet Gap in a Quinoidal 1,6-Methano[10]annulene Resulting from Baird’s 4nπ-Electron Triplet Stabilizati…
2015
A theoretical study of the electronic spectrum of styrene
1999
Abstract The electronic spectrum of styrene has been studied by using multiconfigurational second-order perturbation theory (CASPT2). The study includes geometry optimization of the ground state, the lowest triplet state, and the lowest singlet excited state. The covalent 2 1 A ′ state placed vertically at 4.34 eV is assigned to the first band. The 1 1 A ′→3 1 A ′ transition located at 4.97 eV is responsible for the second band. The most intense feature involves the 5 1 A ′ state, which is calculated to lie 6.19 eV above the ground state. The lowest singlet–singlet Rydberg transition (3s) is predicted to occur at 5.85 eV.