Strategies for Computer-Aided Discovery of Novel Open-Shell Polymers

Organic π-conjugated polymers with a triplet ground state have been the focus of recent research for their interesting and unique electronic properties, arising from the presence of the two unpaired electrons. These polymers are usually built from alternating electron-donating and electron-accepting monomer pairs which lower the HOMO-LUMO gap and yield a triplet state instead of the typical singlet ground state. In this paper we use density functional theory calculations to explore the design rules that govern the creation of a ground state triplet conjugated polymer, and find that a small HOMO-LUMO gap in the singlet state is the best predictor for the existence of a triplet ground state, compared to previous use of pro-quinoidal character. This work can accelerate the discovery of new stable triplet materials by reducing the computa- tional resources needed for electronic-state calculations and the number of potential candidates for synthesis.

Chirality enhances oxygen reduction

Controlled reduction of oxygen is important for developing clean energy technologies, such as fuel cells, and is vital to the existence of aerobic organisms. The process starts with oxygen in a triplet ground state and ends with products that are all in singlet states. Hence, spin constraints in the oxygen reduction must be considered. Here we show that electron transfer from chiral electrodes to oxygen (oxygen reduction reaction) is enhanced over that from achiral electrodes. We demonstrate lower overpotentials and higher current densities for chiral catalysts versus achiral ones. This finding holds even for electrodes composed of heavy metals with large spin orbit coupling. The effect results from the spin selectivity conferred on the electron current by the chiral assemblies, the chiral induced spin selectivity effect.

S = ½ Heterospin Frustration in a Metal‒Fullerene-Bonded Semiconductive Antiferromagnet

Lithium-ion-encapsulated fullerenes (Li+@C60) are 3D superatoms with rich oxidative states. However, no current studies have reported Li+@C60 as ligands. Here, we report a conductive and magnetically frustrated metal–fullerene-bonded framework {[Cu4(Li+@C60)(L)(py)4](NTf2)(hexane)n (1) prepared from redox-active dinuclear metal complex Cu2(L)(py)4 and lithium-ion-encapsulated fullerene salt (Li+@C60)(NTf2−), where ligand L denotes 1,2,4,5-tetrakis(methanesulfonamido)benzene, py pyridine, and NTf2− the bis(trifluoromethane)sulfonamide anion. Electron donor Cu2(L)(py)2 bonds to acceptor Li+@C60 via eight Cu‒C bonds. Cu–C bond formation stems from spontaneous charge transfer (CT) between Cu2(L)(py)4 and (Li+@C60)(NTf2−) by removing the two-terminal py molecules, yielding triplet ground state [Cu2(L)(py)2]+(Li+@C•‒ 60), evidenced by absorption and electron paramagnetic resonance (EPR) spectra, magnetic properties, and quantum chemical calculations. Moreover, Li+@C•‒ 60 radicals (S = ½) and Cu2+ ions (S = ½) interact antiferromagnetically in triangular spin lattices in the absence of long-range magnetic ordering up to 1.8 K; thus, compound 1 is a potential candidate for an S = ½ quantum spin liquid.

Tuning the Magnetic Properties of Diamagnetic Di-Blatter’s Zwitterion to Antiferro- and Ferromagnetic Diradical

<div>In the quest of obtaining organic molecular magnets based on stable diradicals, we have tuned the inherent zwitterionic ground state of tetraphenylhexaazaanthracene (TPHA), the molecule embraced with two Blatter’s moieties, by adopting two different strategies. In the first strategy, we have increased the length of the coupler between the two radical moieties and observed a transition from zwitterionic ground state to diradicalized state. With larger coupler, remarkably strong ferromagnetic interactions are realized based on DFT and WFT based CASSCF/NEVPT2 methods. An analysis based on extent of spin contamination, CASSCF orbitals occupation numbers, HOMO-LUMO and SOMOs energy gap is demonstrated that marks the transition of ground state in these systems. In another approach, we systematically explore the effect of push-pull substitution on the way to obtain molecules based on TPHA skeleton with diradicaloid state and in some cases, even triplet ground state.</div>

Tuning the Magnetic Properties of Diamagnetic Di-Blatter’s Zwitterion to Antiferro- and Ferromagnetic Diradical

<div>In the quest of obtaining organic molecular magnets based on stable diradicals, we have tuned the inherent zwitterionic ground state of tetraphenylhexaazaanthracene (TPHA), the molecule embraced with two Blatter’s moieties, by adopting two different strategies. In the first strategy, we have increased the length of the coupler between the two radical moieties and observed a transition from zwitterionic ground state to diradicalized state. With larger coupler, remarkably strong ferromagnetic interactions are realized based on DFT and WFT based CASSCF/NEVPT2 methods. An analysis based on extent of spin contamination, CASSCF orbitals occupation numbers, HOMO-LUMO and SOMOs energy gap is demonstrated that marks the transition of ground state in these systems. In another approach, we systematically explore the effect of push-pull substitution on the way to obtain molecules based on TPHA skeleton with diradicaloid state and in some cases, even triplet ground state.</div>

A stable triplet diradical emitter

Molecules with luminescence have been extensively investigated, but luminescence of a stable molecule with a triplet ground state has not been observed. Synthesis of boron-containing radicals have attracted lots of...