Chemical Modelling: Volume 14 (Specialist Periodical Reports, 14) - Hardcover

Duarte, Helio Anderson; De Abreu, Heitor Avelino; Benavides-Riveros, Carlos L.

Hardcover

ISBN 10: 1788010043 ISBN 13: 9781788010047

Verlag: Royal Society of Chemistry, 2018

Inhaltsangabe

Chemical modelling covers a wide range of hot topics and active areas in computational chemistry and related fields. With the increase in volume, velocity and variety of information, researchers can find it difficult to keep up to date with the literature in these areas. Containing both comprehensive and critical reviews, this book is the first stop for any materials scientist, biochemist, chemist or molecular physicist wishing to acquaint themselves with major developments in the applications and theory of chemical modelling.

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Chemical modelling covers a wide range of hot topics and active areas in computational chemistry and related fields. With the increase in volume, velocity and variety of information, researchers can find it difficult to keep up to date with the literature in these areas. Containing both comprehensive and critical reviews, this book is the first stop for any materials scientist, biochemist, chemist or molecular physicist wishing to acquaint themselves with major developments in the applications and theory of chemical modelling.

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Chemical Modelling Volume 14

By J.-O. Joswig, M. Springborg

The Royal Society of Chemistry

Copyright © 2018 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-1-78801-004-7

Contents

Preface Michael Springborg and Jan-Ole Joswig, v, 
Theoretical studies as a tool for understanding the aromatic character of porphyrinoid compounds Heike Fliegl, Rashid Valiev, Fabio Pichierri and Dage Sundholm, 1, 
Atomistic modeling for molecular electronics and spintronics: successes and challenges Carmen Herrmann, 43, 
Recent progress on fermionic exchange symmetry Carlos L. Benavides-Riveros, 71, 
Dynamics and electronic structure of atomic clusters Patricio Fuentalba, Roberto Donoso and Carlos Cárdenas, 107, 
Clusters as catalysts: advantages and challenges Shuchi Gupta, Navjot Kaur, Indu Kumari and Neetu Goel, 126, 
Modeling the oxidation mechanism of pyrite and arsenopyrite – connection to acid rock drainage Hélio Anderson Duarte, Egon Campos Dos Santos, Juliana Cecília de Mendonça Silva, Guilherme Ferreira de Lima and Heitor Avelino de Abreu, 162, 
Energetic processing of PAHs: isomerisation and dissociation Aude Simon and Mathias Rapacioli, 195, 
From graphene to borophene the fascinating 2D materials Ihsan Boustani, 217, 

CHAPTER 1

Theoretical studies as a tool for understanding the aromatic character of porphyrinoid compounds

Heike Fliegl, Rashid Valiev, Fabio Pichierric and Dage Sundholm

DOI: 10.1039/9781788010719-00001

1 Introduction

The scientific interest in porphyrinoid based materials is steady growing, since porphyrinoids are not only of biological relevance, but they also show interesting spectroscopic properties that link them to many possible applications such as near infrared dyes, photovoltaic dyes, field-effect transistors, nonlinear optical materials and nanoelectronic devices. Biomedical applications of porphyrinoids are of particular importance specially for photomedical applications in cancer treatment, such as photodynamic therapy, multimodal imaging, drug delivery and biosensing. Porphyrinoids show also an ability to form complexes with metals with unusual oxidation states and are therefore relevant for catalysis.

The classic porphyrin molecule can formally be regarded as four pyrrole rings connected to each other by methin bridges. Depending on the localization of the two inner pyrrolic hydrogen atoms the molecule is labeled cis- or trans-porphyrin. However, at room temperature the inner hydrogens generally move around inside the porphyrin ring. The more general term porphyrinoids is used for a class of molecules that share the classical porphyrin structure for the macroring but differ for example by bearing various substituents or heteroatoms. Classic porphyrins, chlorins and bacteriochlorins are aromatic molecules satisfying Hückel's (4n + 2) p-electron count rule for aromaticity. There is no doubt that aromaticity is an important concept in chemistry albeit it is still not fully understood and thus continuously under debate. Theoretical calculations have shown that the aromatic pathways of classic porphyrins and porphyrinoids can differ, even though they have an almost the same degree of aromaticity.

Structural modifications of porphyrinoids can be readily achieved experimentally by using organometallic approaches. See for example different routes for synthesis of expanded porphyrins, contracted porphyrins and corroles with aromatic as well as antiaromatic character. In particular, synthesis of Ni(II)–norcorrole has recently received attention, since it is air and water stable and is therefore a suitable cathode-active material in battery applications. Antiaromatic Ni(II)–norcorrole shows an order of magnitude higher electrical conductance as compared to a similar aromatic Ni(II)–porphyrin complex, making the molecule highly attractive as component material for future molecular electronic devices.

Experimental and computational studies show that aromatic pathways of non-classical porphyrins such as carbaporphyrins, where one pyrrolic nitrogen has been replaced by carbon and carbathiaporphyrins, where one pyrrolic nitrogen has been replaced by carbon and another one by sulfur, differ from that of classic porphyrins. The existence of antiaromatic isophlorins was predicted by Woodward already in 196044 and synthesized in 2008 by Reddy and Anand. Isophlorins are examples of air-stable antiaromatic porphyrinoids, which have been obtained by replacing an inner pyrrolic nitrogen atom by another heteroatom such as sulfur or oxygen.

Considering the link between porphyrinoids and various applications of them, it is useful to have a deep understanding of their electronic structure and magnetic properties, in particular when aiming at a tailored design of porphyrin based materials with desired properties. By controlling the number of p electrons that participate in the electron delocalization pathway, one can also adjust the electronic and spectroscopic properties of the porphyrinoids. Through the control of the number of p electrons, the (anti)aromatic character and aromatic pathway can be tuned. However, the electron mobility pathways are not easily experimentally accessible, whereas calculated current densities provide accurate information about the current flow in the molecules when they are exposed to an external magnetic field.

In the present review, we give a brief overview over different computational methods that are currently employed for assessing the degree of aromaticity of porphyrinoids with the main focus on current density calculations and studies performed by us and our coworkers. We decided to avoid the discussion of nucleus independent chemical shift (NICS) studies, because NICS studies have been recently reviewed. However, some advantages and disadvantages of the NICS approaches are briefly discussed. Links between computational studies and experimental works are highlighted. The present review is structured as follows. A number of experimental methods motivating computational studies are briefly sketched in Section 2. In Section 3, we give an overview of some of the available theoretical methods that are used as aromaticity indicators. Recent applications on porphyrinoids and porphyrin based molecules are discussed in Section 4. An outlook is given in Section 5.

2 Experimental methods

Experimentally, aromaticity is related to energetic stabilizations, equalizations of bond lengths, preferred substitution reactions, and magnetic properties that differ from those of nonaromatic molecules. Typical spectroscopic techniques that have been used for characterizing porphyrinoids are nuclear magnetic resonance (NMR), ultraviolet (UV) absorption, magnetic circular dichroism (MCD), electronic circular dichroism (ECD), photoelectron (PE), two-photon absorption (TPA) spectroscopies as well as cyclovoltametric (CV) measurements to mention only the most commonly applied ones.

In the context of aromaticity studies, it is widely accepted that experimental proton nuclear magnetic resonance (1H NMR) chemical shifts predict concordant degrees of aromaticity. The 1H NMR spectra show specific features such as a deshielding and downfield shift for the resonances of the protons that are attached to the exterior part of an aromatic ring. The influence of the aromaticity on the 1H NMR chemical shifts can be explained with the so called ring-current effect. Ring shaped molecules such as porphyrins sustain magnetically induced currents when being...

Details zur Ausgabe

• Verlag: Royal Society of Chemistry
• Erscheinungsdatum: 2018
• Sprache: Englisch
• ISBN 10: 1788010043
• ISBN 13: 9781788010047
• Einband: Gebundene Ausgabe
• Anzahl der Seiten: 254
• Herausgeber: Springborg Michael, Joswig Jan-ole
• Kontakt zum Hersteller: Nicht verfügbar
• Verantwortliche Person: Nicht verfügbar