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Annual Reports Section "C" (Physical Chemistry) (v.108, #00)
Front cover (pp. 1-2).
We describe the self-organization of PCBM and a cyanine dye on chemically patterned surfaces during spin coating from solution. On homogeneous surfaces, a transient bilayer forms, which in a later stage decomposes into PCBM droplets in a matrix of the cyanine dye. On the patterned surface also a PCBM droplet phase develops, but the final film structure is greatly determined by contact line pinning of the PCBM domains to the substrate pattern. Three characteristic morphology regimes separated by wetting transitions were observed for different ratios between the natural domain dimensions and the underlying pattern periodicity. We demonstrate that contact line pinning can be an important means to control the film morphology in systems where films are coated from solution. This process can be exploited as a general and versatile method for patterning small semiconducting molecules into 1D and 2D photonic crystals.
Contents list (pp. 3-8).
Surface functionalized poly(ethylene-co -methacrylic acid) (PE-co -MAA) nanofibrous membranes were successfully prepared and applied as solid supports to immobilize photosensitizers. Several activation agents were used to facilitate the surface functionalization of PE-co -MAA nanofibrous membranes, and PCl5 was found to be the most efficient one to activate surface carboxylic acid groups. Three spacers with variable lengths were introduced to the membrane surfaces prior to immobilizations of protoporphyrin IX (PPIX), a photosensitizer. The results revealed that the membranes with longer spacer chain incorporated more photoactive macrocyclic compounds, and the supported PPIX provided a more powerful catalytic effect on the photo-oxidation of 1,5-dihydroxynaphthalene. After five times of repeated catalytic reactions, the catalytic activity of the solid supported PPIX was maintained at 80% of the original power, and the membrane morphology was intact. The nanofibrous membrane supported photosensitizer provided high catalytic activity, easy handling, good durability and reusability.
Coriolis coupling effect in molecular reaction dynamics by Tianshu Chu; Keli Han (pp. 10-33).
In this chapter, we introduce the recent advances in exploring and analyzing the role that Coriolis coupling played in molecular collision dynamics. For this purpose, both the CC and the CS calculations that with/without Coriolis couplings are carried out and compared for a series of collision dynamics including nonadiabatic and adiabatic ones. In particular, such investigation under the nonadiabatic collision dynamics has been achieved with our recently developed quantum dynamical methods and codes. We aimed to provide a rather comprehensive and systematic analysis of Coriolis coupling effect on molecular collisions, which can benefit quantum dynamics calculations and our understanding of reaction dynamics.
Optical differential reflectance spectroscopy on thin molecular films by Roman Forker; Marco Gruenewald; Torsten Fritz (pp. 34-68).
Optical spectroscopy is a powerful tool to study in depth manifold physical processes occurring in molecular solids, at interfaces between molecules and substrates, and at interfaces between different molecular species. Apart from probing the optical interactions themselves, also structural information can be deduced due to the sensitive dependence of the optical properties of molecular assemblies on the respective structure. In our contribution we review the method Differential Reflectance Spectroscopy (DRS), with special emphasis on the interpretation of the spectral data and the extraction of the material's properties, i.e. , the complex dielectric function. We further elucidate which physical effects can be investigated. For this purpose we assess recent progress of DRS experiments and explain several selected results achieved with this technique.
CH/π interactions by Seiji Tsuzuki (pp. 69-95).
Recent gas phase measurements and high level ab initio calculations of the CH/π interactions show that the nature of the CH/π interactions is significantly different from conventional hydrogen bonds, although the CH/π interactions were often regarded as the weakest class of hydrogen bonds. A clear correlation between the binding energies of the benzene clusters with alkanes in the gas phase and the polarizabilities of alkanes was reported. The correlation suggests that the dispersion interaction is the major source of the attraction of the CH/π interactions. Ab initio calculations also show that the major source of attraction in the CH/π interactions is the dispersion interaction and the electrostatic contribution is small. The nature of the “typical CH/π interactions is close to that of van der Waals interactions, if some exceptional “activated” CH/π interactions of highly acidic C–H bonds (C–H bonds of acetylene and chloroform) are excluded. Conventional hydrogen bonds are sufficiently strong and directional due to the large contribution of the highly orientation dependent electrostatic interactions to the attraction. The hydrogen bond is important in controlling structures of molecular assemblies, since the hydrogen bond is sufficiently strong and directional. On the other hand the “typical” CH/π interactions are weak and their directionality is very weak. Although the “typical” CH/π interactions are often regarded as important interactions in controlling the structures of molecular assemblies as in the cases of conventional hydrogen bonds, the importance of the “typical” CH/π interactions is questionable.
Computational methods for studies of semiconductor quantum dots and rings by Dage Sundholm; Tommy Vänskä (pp. 96-125).
The derivation of an effective-mass Hamiltonian for studies of electron–hole pairs (multiexcitons) confined in semiconductor heterostructures such as quantum dots and quantum rings is presented. The obtained Schrödinger equation, describing the dynamics of the electrons and holes trapped in the quantum heterostructures, are solved at the Hartree-Fock self-consistent field, configuration interaction, and coupled-cluster levels. The computational methods, which are familiar from quantum chemical studies on molecules, have been generalized for simultaneously considering electrons and holes at the same level of theory. The methods and implementation of the ab initio computational methods including methods to calculate radiative recombination rates of multiexcitons and exciton relaxation rates due to phonon-multiexciton interaction are described. The applicability of the methods is demonstrated by studying multiexciton energies, photoluminescence spectra, and phonon relaxation rates of electrons trapped in quantum dots, quantum rings, and concentric quantum double rings. The calculations on the quantum dots and quantum rings show the importance of considering charge-carrier correlation effects in studies of energy levels and photoluminescence spectra, only the results obtained at highly correlated levels agree well with available experimental data. The calculations are also found to provide information about the dynamics of the charge carriers confined in the quantum heterostructures that supports novel interpretations of the photoluminescence experiments.
Studies of ion transfer across liquid membranes by electrochemical techniques by Ángela Molina; Carmen Serna; Joaquín A. Ortuño; Encarnación Torralba (pp. 126-176).
The fundamentals and recent advances in ion transfer across the interface between two immiscible electrolyte solutions (ITIES) are reviewed. The different strategies developed to overcome the limitations of the traditional experimental studies with ITIES and to broaden its scope of applications are discussed. Special attention is given to studies of ion transfer through liquid membranes which contain two ITIES, one or both of which can be polarized. Theoretical and experimental studies on the application of different galvanostatic and potentiostatic electrochemical techniques to the study of such systems are described, emphasizing their unique characteristics. The article also includes sections devoted to facilitated ion transfer, liquid/liquid micro-interfaces and the use of weakly supported media.
NMR studies of oxide-based glasses by Mattias Edén (pp. 177-221).
Solid-state nuclear magnetic resonance (NMR) spectroscopy offers an array of options for exploring structural order of amorphous materials both over short (≲0.3 nm) and medium (≲1 nm) ranges. We review the advances reported in the literature for characterizing the structures of oxide-based glasses over roughly the past 15 years. Besides describing the current understanding of basic short-range structural aspects of binary and ternary glass systems that typically involve a single glass modifier and one (silicates and phosphates) or two (e.g. , aluminosilicates, aluminophosphates and silicophosphates) network formers, we focus on illustrating the progress made for revealing intermediate-range structural order, such as extracting information about connectivities among the basic building blocks in the glass networks and how more extended structural motifs may be identified. By assuming only relatively basic background in solid-state NMR and/or the structure of glasses, we hope this review will appeal to newcomers of either area.
Quantum-chemical embedding methods for treating local electronic excitations in complex chemical systems by André Severo Pereira Gomes; Christoph R. Jacob (pp. 222-277).
Quantum chemistry has become an invaluable tool for studying the electronic excitation phenomena underlying many important chemical, biological, and technological processes. Here, we review quantum-chemical approaches for modeling such phenomena. In particular, embedding methods can be particularly useful for treating localized excitations in complex chemical systems. These split the total system into a number of interacting subsystems. The electronic excitations processes occurring in the subsystem of interest are then treated with high accuracy, while its environment is taken into account in a more approximate way. In this review, we use a formulation based on the formally exact frozen-density embedding theory as our starting point. This provides a common framework for discussing the different embedding approaches that are currently available. Moreover, it also forms the basis of emerging methods that allow for a seamless coupling of density-functional theory and wavefunction based approaches, both for ground and excited states. These provide new possibilities for studying electronic excitations in large systems with predictive quantum-chemical methods.
Back cover (pp. 279-280).
A compact viscous finger in a porous medium destabilizes to form a droplet phase at large flow rates. We present a three dimensional video imaging to study this destabilization phenomenon. The images show that a system-spanning finger is a connected network of a large number of pore-scale fingers which fragment at high flow rates to destabilize the network. The volume occupancy of the droplet distribution in the steady state, arising out of events of break-up and coalescence in the pore scale, shows a non-monotonic behavior, naturally separating sub-pore scale droplets from those which span many pores. An analysis of the motion of the interface between the displacing and the displaced fluids provides evidence that the frequency of the pore scale break-up events increases with the flow rate. For low flow rates, these events are mainly localized near the leading edge of the front. However, for higher flow rates, the pore-scale break-up events extend well-behind the leading edge of the front which prevents the growth of a compact finger and instead promotes the formation of a droplet phase.