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IssueVolume 12, Issue 71205-1391May 9, 2011
Cover Picture
Free Access
Cover Picture: The Brightest Fullerene: A New Isotope Effect in Molecular Fluorescence and Phosphorescence (ChemPhysChem 7/2011)
- Pages: 1205
- First Published: 04 May 2011
The cover picture shows the effect of 13C on the excited‐state kinetics of the fullerene C70, described on p. 1247 by C. Baleizão and M. N. Berberan‐Santos. Substitution of 12C by 13C in C70 leads to major changes in its delayed fluorescence and phosphorescence properties. Delayed fluorescence lifetime (τDF) as a function of delayed fluorescence intensity (IDF/IPF) is shown in the graph for 12C70 (squares) and 13C70 (stars) in polystyrene, and from the linear fit to the experimental points it is possible to obtain the quantum yield of triplet formation: 0.994 for 13C70 and 0.990 for 12C70. The hitherto unknown effect of 13C on molecular luminescence, also observed for C60, decreases the internal conversion and T1→So intersystem crossing rates by a mass effect, and increases the S1←T1 back intersystem crossing rate by a nuclear magnetic effect. A small increase (0.4%) in the quantum yield of triplet formation leads to the doubling of the high‐temperature fluorescence quantum yield. As a consequence, 13C70 is by far the brightest fullerene known, attaining a maximum fluorescence quantum yield of 9%. This upper value (equation depicted on the right) results from a large number of excited‐state cycles of the type S1→T1→S1 (as many as 170, on average) that increase the probability of decay through fluorescence. The strong delayed fluorescence intensities and long delayed fluorescence lifetimes of 13C70 render this isotopologue a serious candidate for optical oxygen sensors with unprecedented detection limits at the ppbv level.
Inside Cover
Free Access
Inside Cover: Intermolecular Interactions in Photodamaged DNA from Density Functional Theory Symmetry‐Adapted Perturbation Theory (ChemPhysChem 7/2011)
- Pages: 1206
- First Published: 04 May 2011
The interactions of two consecutive pyrimidines in DNA with their adjacent residues decrease under photoinduced reaction to the CPD lesion. DFT‐SAPT predicts a loss in the interaction energy of 5.8 kcal mol−1, mostly due to weakening of H‐bonding, as shown on p. 1251 by M. Schütz et al.
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Spotlights on our sister journals: ChemPhysChem 7/2011
- Pages: 1218-1220
- First Published: 04 May 2011
Review
Fluctuation Spectroscopy: A New Approach for Studying Low‐Dimensional Molecular Metals
- Pages: 1222-1245
- First Published: 04 March 2011
Come on feel the noise: Fluctuation spectroscopy is described as a new tool to study the dynamics of charge carriers in organic conductors. In these materials the interplay of low dimensionality (see picture), strong electronic correlations and electron–lattice interactions give rise to a rich phenomenology of ground states. Intramolecular modes of lattice vibrations and the inhomogeneous coexistence region of antiferromagnetic (Mott) insulating and superconducting phases are discussed.
Communications
The Brightest Fullerene: A New Isotope Effect in Molecular Fluorescence and Phosphorescence
- Pages: 1247-1250
- First Published: 23 March 2011
The brightest one: Substitution of 12C by 13C in C70 leads to major changes in its delayed fluorescence and phosphorescence properties (see graphs). This new isotope effect decreases the internal conversion and T1→S0 intersystem crossing rates by a mass effect, and increases the S1←T1 intersystem crossing rate by a nuclear magnetic effect. It is also shown that 13C70 is by far the brightest fullerene known.
Intermolecular Interactions in Photodamaged DNA from Density Functional Theory Symmetry‐Adapted Perturbation Theory
- Pages: 1251-1254
- First Published: 30 March 2011
Burnt by the sun: Two adjacent pyrimidine bases in DNA easily react under solar irradiation to the cyclobutane pyrimidine dimer (CPD) lesion (see picture). Density functional theory symmetry‐adapted perturbation theory calculations predict a destabilization of the intermolecular interaction between the pyrimidine bases and the adjacent residues by 6 kcal mol−1 in the course of this transformation. Primarily one particular Watson–Crick base‐pair interaction is affected.
Semiquinone Intermediates in the Two‐Electron Reduction of Quinones in Aqueous Media and their Exceptionally High Reactivity towards Oxygen Reduction
- Pages: 1255-1257
- First Published: 19 April 2011
Catalytic oxygen reduction: Anthraquinone‐mediated oxygen reduction is of significance both industrially and biologically. Herein it is demonstrated how the observed voltammetric response is significantly influenced by the reactivity of the formed semiquinone intermediate (see picture). Further modelling of the system on the basis of a “scheme of squares” allows the solution‐phase rates of reaction to be analysed.
On the Importance of the Dispersion Energy for the Thermodynamic Stability of Molecules
- Pages: 1258-1261
- First Published: 28 March 2011
Action at a distance: By comparing computational data with a large body of experimental data it is shown that larger molecules are significantly more influenced by intramolecular dispersion energy than smaller ones. Because dispersion is always attractive (energy‐lowering) this means that larger molecules are thermodynamically stabilized by dispersion compared to small systems (see graph).
Nanoscale Patterning of Multicomponent Proteins by Bias‐Assisted Atomic Force Microscopy Nanolithography
- Pages: 1262-1265
- First Published: 18 March 2011
Well‐assisted nanopatterns: A new route to fabricate multicomponent protein nanopatterns by combining bias‐assisted atomic force microscopy nanolithography and aptamer–protein recognition is presented. Two types of aptamer arrays for anchoring platelet‐derived growth‐factor‐BB and thrombin (see picture) are introduced [Eg3‐SH: 11‐mercaptoundecyl‐tri(ethylene glycol)].
Articles
Growth of Textured Adenine Thin Films to Exhibit only Chiral Faces
- Pages: 1267-1271
- First Published: 04 April 2011
Getting a grip on handedness: Surface X‐ray diffraction studies show that the prochiral adenine molecule grows on gold, exposing homochiral and biocompatible surfaces in the process. The resulting structure has p2 symmetry as also shown by the STM images. The formed chiral surfaces might find applications in enantioselective heterogeneous catalysis and the pharmaceutical industries.
Dissociative Electron Attachment to β‐Alanine
- Pages: 1272-1279
- First Published: 20 April 2011
Broken down into chunks: Rich fragmentation is observed for the amino acid β‐alanine upon low‐energy electron impact. It involves simple or multiple bond cleavage (see picture), mediated for most fragments by resonances located at around 3, 5.5, and 9 eV.
Towards Mixed Fuels: The Electrochemistry of Hydrazine in the Presence of Methanol and Formic Acid
- Pages: 1280-1287
- First Published: 08 April 2011
Two are better than one: The electrochemistry of solutions containing both of the common fuel cell fuels formic acid and hydrazine is discussed. Both are oxidised at similar potentials at platinum, with hydrazine oxidation proceeding even at electrodes poisoned by formic acid (see voltammograms), demonstrating that their combination in a single fuel might lead to higher power density and more gravimetrically efficient fuel cells.
Correlation between Luminescence and EPR Spectroscopy as Evidence of Ytterbium Pair Formation in Li6Ln(BO3)3:Yb3+ (Ln=Gd, Y) Borate Single Crystals
- Pages: 1288-1293
- First Published: 19 April 2011
Emission spectra of an Yb‐doped borate single crystal (see picture) show an unexpected multiplication of the 2F5/2‐2F7/2 transitions around 975 nm. The crystals are investigated by means of X‐ray diffraction and EPR spectroscopy. The results suggest the existence of two kinds of Yb3+ ions in the single crystals.
Photochromism and Metal Complexation of a Macrocyclic Styryl Naphthopyran
- Pages: 1294-1301
- First Published: 26 April 2011
Now you see it…︁: The behavior of the hybrid biphotochromic system based on a thermally reversible naphthopyran and an alkaline‐earth cation binding benzo‐15‐crown‐5 macrocycle linked by a photochemically bistable stilbene moiety is discussed (see picture).
Multi‐Field Effect on the Electronic Properties of Silicon Nanowires
- Pages: 1302-1309
- First Published: 27 April 2011
The quantum confinement and electronic properties of silicon nanowires (SiNWs) under an external strain field ε and an electric field E are systematically investigated using density functional theory (see graph). These two fields exist in working environments of integrated circuits.
Probing Peptide–Inorganic Surface Interaction at the Single Molecule Level Using Force Spectroscopy
- Pages: 1310-1316
- First Published: 12 April 2011
Single molecule level: The surface interaction of the D‐Ala‐D‐Ala peptide with a stainless steel surface is measured by means of single molecule force spectroscopy (see picture). An average unbinding force in the range of 50–300 pN depending on the loading rate is found, suggesting weak interactions of the peptide with the surface due to a combination of van der Waals and hydrogen bonds.
Size‐, Shape‐ and Composition‐Dependent Alloying Ability of Bimetallic Nanoparticles
- Pages: 1317-1324
- First Published: 12 April 2011
Enthalpies and Gibbs free energies of formation of bimetallic nanoparticles are calculated based on the surface‐area‐difference model considering size and shape effects. Contrary to the positive formation enthalpy of bulk immiscible bimetallic systems, a negative formation enthalpy is obtained when the particles are smaller than a critical size, indicating the alloying process may take place for these small particles (see picture).
Understanding the Influence of Guest–Host Interactions on the Conformation of Short Peptides in a Hydrophobic Cavity: A Computational Study
- Pages: 1325-1333
- First Published: 28 March 2011
Peptides in a self‐assembled cage: A computational study reveals that the conformation of a peptide within a cage, as revealed by the crystal structure, does not correspond to its lowest‐energy conformation in vacuum, due to the ZnO bond formed between the peptide and the cage, and the confinement effect of the cage (see picture).
Inelastic Neutron Scattering Study of PtII Complexes Displaying Anticancer Properties
- Pages: 1334-1341
- First Published: 27 April 2011
PtII anticancer drugs are studied by inelastic neutron scattering (INS) spectroscopy coupled to density functional theory calculations (see picture). The experimental spectra are assigned in the light of the calculated INS transition frequencies and intensities. Good‐quality spectra are obtained, even for very small samples.
Cucurbit[7]uril: Surfactant Host–Guest Complexes in Equilibrium with Micellar Aggregates
- Pages: 1342-1350
- First Published: 06 April 2011
Inclusion complexes: The values of the binding constants Ks between cucurbit[7]uril and trimethylalkylammonium surfactants (see picture) are essentially independent of the length of the hydrocarbon chain of the surfactants. A small percentage of uncomplexed cucurbit[7]uril exists in equilibrium with the cationic micelles and this percentage increases with the hydrophobic character of the surfactants.
Mechanistic Photodissociation of Glycolaldehyde: Insights from Ab Initio and RRKM Calculations
- Pages: 1351-1357
- First Published: 05 April 2011
Mechanistic study: Photodissociation of glycolaldehyde, HOCH2CHO, is studied by quantum chemical calculations. The T1 α‐CC and β‐CO bond fissions following intersystem crossing from the S1 state are the predominant and comparable channels at a low excitation energy of 280–340 nm (see picture). Rate constants for these bond fissions are calculated by Rice–Ramsperger–Kassel–Marcus theory.
The Evolution of Bonding and Thermodynamic Properties of Boron‐Doped Small Carbon Clusters: An Ab Initio Study
- Pages: 1358-1366
- First Published: 12 April 2011
Three possible paths of molecular evolution exist for BCn (n=1–6) clusters (see picture), characterized by different unpaired electron distributions. The energetic and electronic consequences for the increased size of structures differ significantly, which leads to representatives of the ground electronic state from different structural groups.
Theoretical and Experimental Studies on the Mechanism of Coloration of Polyimides
- Pages: 1367-1377
- First Published: 27 April 2011
UV/Vis spectra of polyimides are obtained theoretically by combining long‐range‐corrected time‐dependent density functional theory and classical molecular dynamics. It is confirmed that the coloration of polyimides is significantly affected by intermolecular interactions (see picture).
Effects of Spatial Constraints and Brønsted Acid Site Locations on para‐Terphenyl Ionization and Charge Transfer in Zeolites
- Pages: 1378-1388
- First Published: 29 March 2011
Zeolite topology and acid‐site location exert significant effects on the spontaneous ionization of para‐terphenyl (PP3) to form PP3.+ and on subsequent charge transfer forming electron–hole pairs of types 1 (PP3@H‐Zeo1.−.+) and 2 (PP3@H‐Zeo2.−.+) [see picture]. Spatial constraints determine the stability of transition states and charge‐transfer complexes relevant to charge separation.
Book Review
Industrial Photoinitiators: A Technical Guide. by W. Arthur Green.
- Pages: 1389
- First Published: 19 April 2011
CRC Press 2010, 302 pp., softcover, $ 80.96.—ISBN 978‐1‐4398274‐5‐1
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