Xingyong Wang

Tuning ground states of Bis(triarylamine) Dications: from a closed-shell singlet to a diradicaloid with an excited triplet state

Three bis(triarylamine) dications were isolated by using weakly coordinating anions. Their electronic structures in the ground state were investigated by various experiments in conjunction with theoretical calculations. The ground-state electronic structures of these species were tunable by substituent effects, with two of them as closed-shell singlets and one of them as an open-shell singlet in the solid state. The excited state of the latter is thermally accessible, indicated by EPR and SQUID measurements. The work provides a new and stable diradicaloid structure motif with an excited triplet sate.

Nitrogen Analogues of Thiele’s Hydrocarbon

A series of bis[N,N-di-(4-methoxylphenyl)amino]arene dications 1(2+) -3(2+) have been synthesized and characterized. Their electronic structures were investigated by various experiments assisted by theoretical calculations. It was found that they are singlets in the ground state and that their diradical character is dependent on the bridging moiety. 3(2+) has a smaller singlet-triplet energy gap and its excited triplet state is thermally readily accessible. The work provides a nitrogen analogue of Thieles hydrocarbon with considerable diradical character.

Two stable phosphorus-containing four-membered ring radical cations with inverse spin density distributions

Two phosphorus-containing four-membered ring radical cations 1(•+) and 2(•+) have been isolated and characterized by UV-vis absorption spectroscopy, electron paramagnetic resonance (EPR), and single-crystal X-ray diffraction. Compared with neutral molecules 1 and 2, radical 1(•+) has elongated P-P bonds and more pyramidalized phosphorus atoms, while shortened P-Nring distances and larger angles around phosphorus centers are observed for 2(•+). EPR studies indicate that for 1(•+) spin density mainly resides on the exocyclic nitrogen atoms with very minor contribution from endocyclic phosphorus atoms, while the situation is opposite for 2(•+). Such an inverse spin density distribution is controlled by the exocyclic substituents, which is supported by DFT calculations.

A Crystalline Phosphaalkene Radical Anion

Salts containing phosphaalkene radical anions have been isolated and characterized by electron paramagnetic resonance (EPR) spectroscopy, UV-vis absorption spectroscopy, and single-crystal X-ray diffraction. The radical anions feature elongated P-C bonds and an aromatization of fulvene compared to the neutral phosphaalkene. Their EPR spectra and theoretical calculations indicate the spin density of the radicals mainly resides on phosphorus atoms. This work provides the first example of a crystalline phosphaalkene radical anion.

Odd-electron-bonded sulfur radical cations: X-ray structural evidence of a sulfur-sulfur three-electron σ-bond

The one-electron oxidations of 1,8-chalcogen naphthalenes Nap(SPh)2 (1) and Nap(SPh)(SePh) (2) lead to the formation of persistent radical cations 1(•+) and 2(•+) in solution. EPR spectra, UV-vis absorptions, and DFT calculations show a three-electron σ-bond in both cations. The former cation remains stable in the solid state, while the latter dimerizes upon crystallization and returns to being radical cations upon dissolution. This work provides conclusive structural evidence of a sulfur-sulfur three-electron σ-bond (in 1(•+)) and a rare example of a persistent heteroatomic three-electron σ-bond (in 2(•+)).

Reversible σ-Dimerizations of Persistent Organic Radical Cations†

A class of well-defined reversible σ-dimerizations of 9,10-dialkoxyanthracene radical cations are presented. Yellow crystals of the σ-dimerized dication dissociate to purple solutions of monomeric radical cations in solution. The identity and stability of radical cations were unequivocally confirmed, providing evidence for reversible σ-dimerizations of persistent radical cations of aromatic systems.

Synthesis, Characterization, and Structures of a Persistent Aniline Radical Cation†

is regularly stacked along the b axis by C H···pintermolecular interactions. The interplanar distances arearound5.1 ,muchlargerthantheequilibriumvanderWaalsseparation of 3.4 , indicating that there are no intermolec-ular p–p interactions (Figure S6 in the Supporting Informa-tion). The phenyl ring of the TBAC

Isolation and reversible dimerization of a selenium–selenium three-electron σ-bond

Three-electron σ-bonding that was proposed by Linus Pauling in 1931 has been recognized as important in intermediates encountered in many areas. A number of three-electron bonding systems have been spectroscopically investigated in the gas phase, solution and solid matrix. However, X-ray diffraction studies have only been possible on simple noble gas dimer Xe∴Xe and cyclic framework-constrained N∴N radical cations. Here, we show that a diselena species modified with a naphthalene scaffold can undergo one-electron oxidation using a large and weakly coordinating anion, to afford a room-temperature-stable radical cation containing a Se∴Se three-electron σ-bond. When a small anion is used, a reversible dimerization with phase and marked colour changes is observed: radical cation in solution (blue) but diamagnetic dimer in the solid state (brown). These findings suggest that more examples of three-electron σ-bonds may be stabilized and isolated by using naphthalene scaffolds together with large and weakly coordinating anions.

Stabilizing radical cation and dication of a tetrathiafulvalene derivative by a weakly coordinating anion

After the chemical oxidation of the neutral tetrakis(methylthio)tetrathiafulvalene (TMT-TTF, 1) by specific oxidation agents with weakly coordinating anion, [Al(ORF)4](-) [ORF = OC(CF3)3], the radical cation TMT-TTF(•+) (1(•+)) and dication TMT-TTF(2+) (1(2+)) were successfully stabilized and isolated. All the compounds are well-soluble in some solvents and have been systematically investigated by absorption spectra, (1)H NMR, electron paramagnetic resonance (EPR) measurements. Their crystal structures and electronic properties have been studied in conjunction with theoretical calculation. The synthetic approach for chemical oxidation by specific salts of weakly coordinating anions is useful for stable radical cations of tetrathiafulvalene (TTF) and its derivatives in both solution and solid state, which will extend the further research, including structure-property relations on stable radicals for TTF derivatives and new functional materials based on them.

Modulation of biointeractions by electrically switchable oligopeptide surfaces : structural requirements and mechanism

Understanding the dynamic behavior of switchable surfaces is of paramount importance for the development of controllable and tailor-made surface materials. Herein, electrically switchable mixed self-assembled monolayers based on oligopeptides have been investigated in order to elucidate their conformational mechanism and structural requirements for the regulation of biomolecular interactions between proteins and ligands appended to the end of surface tethered oligopeptides. The interaction of the neutravidin protein to a surface appended biotin ligand was chosen as a model system. All the considerable experimental data, taken together with detailed computational work, support a switching mechanism in which biomolecular interactions are controlled by conformational changes between fully extended (“ON” state) and collapsed (“OFF” state) oligopeptide conformer structures. In the fully extended conformation, the biotin appended to the oligopeptide is largely free from steric factors allowing it to efficiently bind to the neutravidin from solution. While under a collapsed conformation, the ligand presented at the surface is partially embedded in the second component of the mixed SAM, and thus sterically shielded and inaccessible for neutravidin binding. Steric hindrances aroused from the neighboring surface-confined oligopeptide chains exert a great influence over the conformational behaviour of the oligopeptides, and as a consequence, over the switching efficiency. Our results also highlight the role of oligopeptide length in controlling binding switching efficiency. This study lays the foundation for designing and constructing dynamic surface materials with novel biological functions and capabilities, enabling their utilization in a wide variety of biological and medical applications.