Acenes have long been the subject of intense study because of the unique electronic properties associated with their pi-bond topology. Recent reports of impressive semiconductor properties of larger homologues have reinvigorated research in this field, leading to new methods for their synthesis, functionalization, and purification, as well as for fabricating organic electronic components. Studies performed on high-purity acene single crystals revealed their intrinsic electronic properties and provide useful benchmarks for thin film device research. New approaches to add functionality were developed to improve the processability of these materials in solution. These new functionalization strategies have recently allowed the synthesis of acenes larger than pentacene, which have hitherto been largely unavailable and poorly studied, as well as investigation of their associated structure/property relationships.

The larger acenes: versatile organic semiconductors.

A method of description of the chemical bonding combining the compactness and intuitive simplicity of Lewis theory with the flexibility and generality of canonical molecular orbital theory is presented, which is called adaptive natural density partitioning. The objects of chemical bonding in this method are n-center 2-electron bonds, where n goes from one (lone-pair) to the maximum number of atoms in the system (completely delocalized bonding). The algorithm is a generalization of the natural bonding orbital analysis and is based on the diagonalization of the blocks of the first-order density matrix in the basis of natural atomic orbitals. The results obtained by the application of the algorithm to the systems with non-classical bonding can be readily interpreted from the point of view of aromaticity/antiaromaticity concepts. The considered examples include Li4 cluster and a family of planar boron clusters observed in molecular beams.

Developing paradigms of chemical bonding: adaptive natural density partitioning.

An energy decomposition analysis (EDA) method is proposed to isolate physically relevant components of the total intermolecular interaction energies such as the contribution from interacting frozen monomer densities, the energy lowering due to polarization of the densities, and the further energy lowering due to charge-transfer effects. This method is conceptually similar to existing EDA methods such as Morokuma analysis but includes several important new features. The first is a fully self-consistent treatment of the energy lowering due to polarization, which is evaluated by a self-consistent field calculation in which the molecular orbital coefficients are constrained to be block-diagonal (absolutely localized) in the interacting molecules to prohibit charge transfer. The second new feature is the ability to separate forward and back-donation in the charge-transfer energy term using a perturbative approximation starting from the optimized block-diagonal reference. The newly proposed EDA method is used to understand the fundamental aspects of intermolecular interactions such as the degree of covalency in the hydrogen bonding in water and the contributions of forward and back-donation in synergic bonding in metal complexes. Additionally, it is demonstrated that this method can be used to identify the factors controlling the interaction of the molecular hydrogen with open metal centers in potential hydrogen storage materials and the interaction of methane with rhenium complexes.

Unravelling the origin of intermolecular interactions using absolutely localized molecular orbitals.

to Planar Systems Tadeusz M. Krygowski,*,† Halina Szatylowicz,*,‡ Olga A. Stasyuk,‡ Justyna Dominikowska, and Marcin Palusiak †Department of Chemistry, Warsaw University, Pasteura 1, 02-093 Warsaw, Poland ‡Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland Department of Theoretical and Structural Chemistry, Faculty of Chemistry, University of Łod́z,́ Pomorska 163/165, 90-236 Łod́z,́ Poland

Aromaticity from the viewpoint of molecular geometry: application to planar systems.

Acene werden wegen ihrer einzigartigen elektronischen Eigenschaften, die auf der Topologie ihrer π-Systeme beruhen, seit langem untersucht. Berichte uber die bemerkenswerten Halbleitereigenschaften hoherer Homologe haben in letzter Zeit zu verstarkten Forschungsaktivitaten gefuhrt. Es wurden neue Verfahren zur Synthese, Funktionalisierung und Reinigung sowie zur Herstellung organoelektronischer Bauteile entwickelt. Durch Untersuchungen an hochreinen Acen-Einkristallen wurden die charakteristischen elektronischen Eigenschaften und Kenngrosen fur die Beurteilung von Dunnschichtbauteilen ermittelt. Um die Verarbeitbarkeit in Losung zu verbessern, wurden neuartige Funktionalisierungsmethoden entwickelt. Die fur elektronische Anwendungen erwunschten Eigenschaften nichtfunktionalisierter Acene bleiben bei der Funktionalisierung erhalten. Mit diesen Verfahren wurden kurzlich Derivate hoherer Acene als Pentacen, die zuvor kaum zuganglich waren, erhalten, sodass Struktur-Eigenschafts-Beziehungen untersucht werden konnten.

Höhere Acene: vielseitige organische Halbleiter

Molecular aromaticity in the linear polyacenes is investigated using an atoms in molecules based six center index (SCI-AIM) which measures the electron delocalization. SCI-AIM values for the linear polyacenes indicate decreasing aromaticity going from outer to inner rings in the polyacene series. The SCI-AIM approach is compared to a Mulliken-like approach, and a critical comparison to the PDI index is made.

Electron delocalization and aromaticity in linear polyacenes: Atoms in molecules multicenter delocalization index

We present a novel algorithm to integrate property densities over the volume of a quantum topological atom. Atoms are grown outward, starting from a sphere centered on the nucleus, by means of a finite element meshing algorithm. Bond critical points and ring critical points require special treatment. The overall philosophy as well as intricate features of this meshing algorithm are given, followed by details of the quadrature over the finite elements. An effort has been made to design a streamlined and compact algorithm, focusing on the core of challenges arising in tracing the electron density's gradient vector field. The current algorithm also generates a new type of pictures that can be a Graphical User Interface. Excellent integration errors, L(Ω), are obtained, even for atoms with (narrow) tails or sharp corners. © 2007 Wiley Periodicals, Inc. J Comput Chem 2007

Visualization and integration of quantum topological atoms by spatial discretization into finite elements

In this article, we describe and apply an algorithm that visualizes atoms and bonds in molecules and van der Waals complexes, based on the topology of the electron density. The theory of quantum chemical topology defines both atoms and bonds via a single consistent procedure, and enables the association of an atomic shape with an atomic property (charge, dipole moment, volume, ...). Special attention is paid to the bridging of gaps arising in interatomic surfaces, in the presence of ring critical points or high ellipticity. This algorithm, in conjunction with the graphical user interface of the computer program MORPHY enables robust and efficient rendering of complicated interatomic surfaces, as found in larger systems.

Rendering of quantum topological atoms and bonds.

Traditionally force fields express 1,3 and 1,4 interactions as bonded terms via potentials that involve valence and torsion angles, respectively These interactions are not modeled by point charge terms, which are confined to electrostatic interactions between more distant atoms (1,n where n>4) Here we show that both 1,3 and 1,4 interactions can be described on the same footing as 1,n (n>4) interactions by a convergent multipole expansion of the Coulomb energy of the participating atom pairs The atomic multipole moments are generated by the theory of quantum chemical topology The procedure to make the multipole expansion convergent is based on a “shift procedure” described in earlier work [L Joubert and P L A Popelier, Molec Phys 100, 3357 (2002)]

Michel Rafat

Papers

Electron delocalization and aromaticity in linear polyacenes: Atoms in molecules multicenter delocalization index

Visualization and integration of quantum topological atoms by spatial discretization into finite elements

Rendering of quantum topological atoms and bonds.

A convergent multipole expansion for 1,3 and 1,4 Coulomb interactions

Topological Atom–Atom Partitioning of Molecular Exchange Energy and its Multipolar Convergence