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1. Thiophene‐Based Double Helices: Radical Cations with SOMO–HOMO Energy Level Inversion ^†

   https://doi.org/10.1111/php.13475  

   Rajca, Andrzej; Shu, Chan; Zhang, Hui; Zhang, Sheng; Wang, Hua; Rajca, Suchada (July 2021, Photochemistry and Photobiology)

   Abstract We report relatively persistent, open‐shell thiophene‐based double helices, radical cations 1^•+‐TMS₁₂and 2^•+‐TMS₈. Closed‐shell neutral double helices, 1‐TMS₁₂and 2‐TMS₈, have nearly identical first oxidation potentials,E^+/0 ≈ +1.33 V, corresponding to reversible oxidation to their radical cations. The radical cations are generated, using tungsten hexachloride in dichloromethane (DCM) as an oxidant,E^+/0 ≈ +1.56 V. EPR spectra consist of a relatively sharp singlet peak with an unusually lowg‐value of 2.001–2.002, thus suggesting exclusive delocalization of spin density over π‐conjugated system consisting of carbon atoms only. DFT computations confirm these findings, as only negligible fraction of spin density is found on sulfur and silicon atoms and the spin density is delocalized over a single tetrathiophene moiety. For radical cation, 1^•+‐TMS₁₂, energy level of the singly occupied molecular orbital (SOMO) lies below the four highest occupied molecular orbitals (HOMOs), thus indicating the SOMO–HOMO inversion (SHI) and therefore, violating the Aufbau principle. 1^•+‐TMS₁₂has a half‐life of the order of only 5 min at room temperature. EPR peak intensity of 2^•+‐TMS₈, which does not show SHI, is practically unchanged over at least 2 h. 

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2. Geometric and electronic structure of a crystallographically characterized thiolate-ligated binuclear peroxo-bridged cobalt(III) complex

   https://doi.org/10.1007/s00775-019-01686-x  

   Dedushko, Maksym A.; Schweitzer, Dirk; Blakely, Maike N.; Swartz, Rodney D.; Kaminsky, Werner; Kovacs, Julie A. (January 2019, JBIC Journal of Biological Inorganic Chemistry)

   In order to shed light on metal-dependent mechanisms for O–O bond cleavage, and its microscopic reverse, we compare herein the electronic and geometric structures of O2-derived binuclear Co(III)– and Mn(III)–peroxo compounds. Binuclear metal peroxo complexes are proposed to form as intermediates during Mn-promoted photosynthetic H2O oxidation, as well as a Co-containing artificial leaf inspired by nature’s photosynthetic H2O oxidation catalyst. Crystallographic characterization of an extremely activated peroxo is made possible by working with substitution-inert, low-spin Co(III). Density functional theory (DFT) calculations show that the frontier orbitals of the Co(III)–peroxo compound differ noticeably from the analogous Mn(III)–peroxo compound. The highest occupied molecular orbital (HOMO) associated with the Co(III)–peroxo is more localized on the peroxo in an antibonding π*(O–O) orbital, whereas the HOMO of the structurally analogous Mn(III)–peroxo is delocalized over both the metal d-orbitals and peroxo π*(O–O) orbital. With low-spin d6 Co(III), filled t2g orbitals prevent π-back-donation from the doubly occupied antibonding π*(O–O) orbital onto the metal ion. This is not the case with high-spin d4 Mn(III), since these orbitals are half-filled. This weakens the peroxo O–O bond of the former relative to the latter. 

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3. Synthesis, Structures, and Properties of Dehydrobiphenyleno[12]Annulenes: Carbon‐Rich Compounds Comprising Two Different Antiaromatic Units

   https://doi.org/10.1002/asia.202500754  

   Suzuki, Komari; Asai, Daisuke; Herman, Robert J; Njoroge, Sheila W; Yoshida, Satoshi; Sato, Sota; Lee, Semin; Tahara, Kazukuni (September 2025, Chemistry – An Asian Journal)

   Abstract In this work we report the synthesis, structure, and electronic properties of carbon‐rich compounds dehydrobiphenyleno[12]annulenes (DBP[12]As) comprising antiaromatic four‐membered rings (4MR) and 12‐membered ring (12MR). Ultraviolet–visible absorption spectra and electrochemical behaviors of DBP[12]As confirmed their relatively narrow highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap values and high HOMO energy levels, which were supported by density functional theory simulations. Parent DBP[12]A adopts a slipped herringbone structure in a crystalline state, with the molecules forming 1D stacks via π–π interactions. The experimentally derived bond lengths, bonding analyses using the Wiberg bond indices, and localized orbital locator calculation support a stronger double bond character for the 12MR bonds than the 4MR bonds in the inner six‐membered ring. The chemical shifts of hydrogens in¹H NMR spectra, as well as magnetically induced ring current analyses using quantum chemical calculations, indicate that the 4MRs have stronger antiaromatic character than the 12MR. The present information is useful for a fundamental understanding of carbon‐rich compounds with different antiaromatic units as well as designing novel molecules with unique electronic properties. 

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4. The effect of solvent on determining highest occupied molecular orbital energies of semiconducting organic molecules: Insight from a combined computational approach

   https://doi.org/10.1002/jcc.27065  

   Kramer, Aaron; Pachter, Ruth; Hsu, Julia W. P.; Vandenberghe, William G. (January 2023, Journal of Computational Chemistry)

   Abstract Although cyclic voltammetry (CV) measurements in solution have been widely used to determine the highest occupied molecular orbital energy (E_HOMO) of semiconducting organic molecules, an understanding of the experimentally observed discrepancies due to the solvent used is lacking. To explain these differences, we investigate the solvent effects onE_HOMOby combining density functional theory and molecular dynamics calculations for four donor molecules with a common backbone moiety. We compare the experimentalE_HOMOvalues to the calculated values obtained from either implicit or first solvation shell theories. We find that the first solvation shell method can capture theE_HOMOvariation arising from the functional groups in solution, unlike the implicit method. We further applied the first solvation shell method to other semiconducting organic molecules measured in solutions for different solvents. We find that theE_HOMOobtained using an implicit method is insensitive to solvent choice. The first solvation shell, however, producesE_HOMOvalues that are sensitive to solvent choices and agrees with published experimental results. The solvent sensitivity arises from a hierarchy of three effects: (1) the solute electronic state within a surrounding dielectric continuum, (2) ambient temperature or solvent atoms changing the solute geometry, and (3) electronic interactions between the solute and solvents. The implicit method, on the other hand, only captures the effect of a dielectric environment. Our findings suggest thatE_HOMOobtained by CV measurements should account for the influence of solvent when the results are reported, interpreted, or compared to other molecules. 

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5. Unique Energy Alignments of a Ternary Material System toward High‐Performance Organic Photovoltaics

   https://doi.org/10.1002/adma.201801501  

   Cheng, Pei; Wang, Jiayu; Zhang, Qianqian; Huang, Wenchao; Zhu, Jingshuai; Wang, Rui; Chang, Sheng‐Yung; Sun, Pengyu; Meng, Lei; Zhao, Hongxiang; et al (May 2018, Advanced Materials)

   Abstract Incorporating narrow‐bandgap near‐infrared absorbers as the third component in a donor/acceptor binary blend is a new strategy to improve the power conversion efficiency (PCE) of organic photovoltaics (OPV). However, there are two main restrictions: potential charge recombination in the narrow‐gap material and miscompatibility between each component. The optimized design is to employ a third component (structurally similar to the donor or acceptor) with a lowest unoccupied molecular orbital (LUMO) energy level similar to the acceptor and a highest occupied molecular orbital (HOMO) energy level similar to the donor. In this design, enhanced absorption of the active layer and enhanced charge transfer can be realized without breaking the optimized morphology of the active layer. Herein, in order to realize this design, two new narrow‐bandgap nonfullerene acceptors with suitable energy levels and chemical structures are designed, synthesized, and employed as the third component in the donor/acceptor binary blend, which boosts the PCE of OPV to 11.6%. 

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