![]() ![]() ![]() 6, 7 Furthermore, in the case of systems with unpaired electrons approximating true zeroth‐order wavefunction with just one state/configuration, i.e., a single Slater determinant in the Hartree–Fock theory, is often just as erroneous. Thus, within the framework of modern quantum mechanics assigning individual electrons to individual orbitals and individual sets of quantum numbers is erroneous only the system (atom, molecule) as a whole possesses well‐defined (sharp) stationary states. When applied to a molecule, this means that all of the occupied orbitals describe all electrons simultaneously, and, while the electrons are indistinguishable, orbitals, by definition, are not. In the present review, we discuss these factors with a particular focus on unconventional orbital occupations and orderings, which lead to unexpected, practically useful or simply interesting chemical entities and behaviors.Īccording to the Pauli exclusion principle, the wavefunction for a system of fermions must be antisymmetric with respect to the interchange of any two particles. 5 Development of such materials requires not only an in‐depth understanding of the factors that control molecular electronic configuration and state, but also thinking outside the box of conventional physical organic chemistry rules. The main difficulty is that of the huge pool of organic radicals only very few are stable against dimerization (persistent), 3, 4 can be crystallized, are not Mott insulators, and provide a clear preference for the desired spin alignment. 2 The state‐of‐the‐art research in the field of organic molecular electronics, including photovoltaics, spin valves, nano switches, field effect transistors, and logic circuits, is targeted at species with a predetermined spin state that can be affected via well defined stimuli. Although historically the latter have been the domain of metals and, in particular, transition metal complexes, in the recent years the focus has shifted toward fully organic functional materials as promising sustainable alternatives for applications ranging from information storage to environmental sensors. While the majority of stable organic molecules have a closed‐shell singlet ground state, species with unpaired electrons display unique chemical reactivity and are capable of carrying magnetism and conductivity functionalities. As orbitals comprise not only the spatial component, but also the spin, they also give rise to such key features as the nature of configuration shell-open or closed-and the multiplicity of the electronic state. 1 This model description, albeit approximate, is nonetheless indispensable in explaining and predicting molecular geometry and various chemical and physical properties. The electronic configuration and state of a molecule characterize the distribution of electrons across the corresponding one‐electron wavefunctions, i.e., orbitals. doi: 10.1002/wcms.1233įor further resources related to this article, please visit the WIREs website. ![]() These peculiar species possess attractive conductive and magnetic properties, and a number of them that have already been developed into molecular electronics applications are highlighted in this review. As a result, the SOMO is not affected by electron attachment to or removal from the molecule, and the products of such redox processes are polyradicals. In such quasi‐closed‐shell systems, the singly occupied molecular orbital ( SOMO) is energetically lower than one or more doubly occupied orbitals. In addition, we outline a range of organic molecules with intriguing non‐aufbau orbital configurations. A number of fascinating chemical systems with spin states that fluctuate between triplet and open‐shell singlet, and are responsive to irradiation, pH, and other external stimuli, are highlighted. While such rules hold in selected simple cases, in general the spin state of a system depends on a combination of electronic factors that include Coulomb and Pauli repulsion, nuclear attraction, kinetic energy, orbital relaxation, and static correlation. In this advanced review, we scrutinize various qualitative rules of orbital occupation and spin alignment, viz., the aufbau principle, Hund's multiplicity rule, and dynamic spin polarization concept, through the prism of quantum mechanics. Organic molecules that have open‐shell ground states and interesting physicochemical properties, particularly those influencing their spin alignment, are of immense interest within the up‐and‐coming field of molecular electronics. The spin state is one of the key characteristics arising from the ordering of electrons within the molecule's set of orbitals. The electronic configuration of the molecule is the foundation of its structure and reactivity. ![]()
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |