Singly Occupied Molecular Orbital−Highest Occupied Molecular Orbital (SOMO−HOMO) Conversion

Abstract

Singly occupied molecular orbital−highest occupied molecular orbital (SOMO−HOMO) conversion (inversion), SHC, is a phenomenon in which the SOMO is lower in energy than the doubly occupied molecular orbitals (DOMO, HOMO). A non-Aufbau electronic structure leads to unique properties such as a switch in bond dissociation energy and the generation of high-spin species on one-electron oxidation. In addition, the pronounced photostability of these species has been reported recently for application in organic light-emitting devices. In this review article, we summarise the chemistry of SOMO−HOMO converted (inverted) species reported to date.

Room-Temperature-Stable Magnesium Electride via Ni(II) Reduction

“… 32 The NNA appears only in the α-electron density and coincides with both the maximum spin density and the orbital HOMO-4, which we identify to be the SOMO of [ 3-Mg 4 ] − , thus indicating SOMO–HOMO inversion. 15 , 42 Evidence in favor of the true electride nature of [ 3-Mg 4 ] − is the negligible electron delocalization between the NNA and the nitrogen or magnesium atoms that is less than 0.05. A low delocalization index between the NNA and the surrounding atoms signifies the dominance of electrostatic interactions between the free electron and the positive Mg(II) centers akin to the ionic compounds.…”

Theoretical Insights into the Substrate-Dependent Diastereodivergence in (3 + 2) Cycloaddition of α-Keto Ester Enolates with Nitrones

“…Several examples of SOMO-HOMO level inversions (SHI), in which the energy of the SOMO is lower than that of the doubly occupied HOMO, have been documented. 42) However, of note, the occurrence of SHI in Ni(II) complexes has only recently been reported. 43) Jeong et al characterized the SHI property in high-spin Ni(II) complexes, which were prepared from Ni(NO 3 ), 1,4,7-trimethyl-1,4,7-triazacyclononane, and 3-hydroxyflavone, as a functional model of quercetin 2,4-dioxygenases.…”

Organic radicals with inversion of SOMO and HOMO energies and potential applications in optoelectronics

“…This SOMO-HOMO inversion (SHI), alternatively referred to as SOMO-HOMO conversion or a quasi-closed-shell configuration, has generated widespread interest, both theoretically and experimentally, to rationalize and understand the consequences of the peculiar electronic structure of this class of open-shell systems. 23,50,[53][54][55][56][57] SHI has been investigated in organic spin-polarized donor systems as a route toward high-spin diradicals, 18,[58][59][60][61][62] and also in the case of luminescent radicals where SHI was associated with a significant increase of photostability. 38 Coote, Corminboeuf et al summarized various theoretical aspects related to the characterization of this phenomenon with molecular examples of SHI in 2015.…”

“…50 Very recently, Abe et al exhaustively surveyed the reported compounds in which SHI has been identified. 55 Given the strong attention that SHI organic radicals have received again recently, it appears timely to review the synthetic challenge to obtain SHI in open-shell compounds, as well as some important new theoretical insight regarding the occurrence of SHI and its impact on the molecular optoelectronic and magnetic properties.…”