A Discrete, Boron-Containing Triangular Triradical.

A neutral boron-containing triangular triradical based on a triptycene derivative has been designed and synthesized. Its structure, bonding and physical property have been studied by EPR spectroscopy, SQUID magnetometry and single crystal X-ray diffraction, as well as theoretical calculations. The triradical has a series of isosceles triangle conformations in the solution due to the Jahn-Teller distortion, leading to the splitting of the two low-lying doublet states. This factor together with negligible spin-orbit coupling (SOC) of composing light atoms quenches the spin frustration. The work represents a rare example of a neutral through-space triangular triradical.

Metal-Free Catalytic Formation of a Donor-Acceptor-Donor Molecule and Its Lewis Acid-Adduct Singlet Diradical with High-Efficient NIR-II Photothermal Conversion.

We have synthesized a quinone-incorporated bistriarylamine donor-acceptor-donor (D-A-D) semiconductor 1 by B(C6F5)3 (BCF) catalyzed C-H/C-H cross coupling via radical ion pair intermediates. Coordination of Lewis acids BCF and Al(ORF)3 (RF=C(CF3)3) to the semiconductor 1 afforded diradical zwitterions 2 and 3 by integer electron transfer. Upon binding to Lewis acids, the LUMO energy of 1 is significantly lowered and the band gap of the semiconductor is significantly narrowed from 1.93 eV (1) to 1.01 eV (2) and 1.06 eV (3). 2 and 3 are rare near-infrared (NIR) diradical dyes with broad absorption both centered around 1500 nm. By introducing a photo BCF generator, 2 can be generated by light-dependent control. Furthermore, the integer electron transfer process can also be reversibly regulated via the addition of CH3CN. In addition, the temperature of 2 sharply increased and reached as high as 110 °C in 10 s upon the irradiation of near-infrared-II (NIR-II) laser (1064 nm, 0.7 W cm-2), exhibiting a fast response to laser. It displays excellent photothermal stability with a photothermal (PT) conversion efficiency of 62.26 % and high-quality PT imaging.

A Dynamic Triradical: Synthesis, Crystal Structure, and Spin Frustration.

Polyradicals, i.e., multispin organic molecules, are playing important roles in radical-based material applications for their spin-spin interaction. A dynamic covalently bonded multispin molecule may endow materials with added function such as memory and switching. However, such a species has yet to be reported. We here report the synthesis, characterization, and crystal structure of a dynamic triradical species. It is generated by the self-assembly of two molecules through a Lewis acid coupled electron transfer. The crystalline species is spin-frustrated without Jahn-Teller distortion at low temperature, while it dissociates back to diamagnetic starting material in solution at high temperature. The reversible process is tracked by variable-temperature NMR, EPR, and UV-vis-NIR spectroscopy. Isolation, property study, and dynamic bonding investigation on such a species lay the foundation for the design of functional polyradicals with potential application as memory or switching devices.

Lewis Acid-Mediated Radical Stabilization and Dynamic Covalent Bonding: Tunable, Reversible and Photocontrollable.

This work describes a strategy not only to isolate a dynamically stable radical with physical property tunability, but to efficiently regulate the radical dissociation with reversibility and photo controllability. The addition of Lewis acid B(C6 F5 )3 (BCF) into the solution of a radical σ-dimer (1-1) led to a stable radical (1⋅-2B), which has been characterized by EPR spectroscopy, UV/Vis spectroscopy and single crystal X-ray diffraction, in conjunction with theoretical calculation. The radical species is stabilized mainly by captodative effect, single electron transfer and steric effect. The absorption maximum of the radical can be tuned by using different Lewis acids. Dimer 1-1 can be achieved back by addition of a stronger base into the solution of 1⋅-2B, exhibiting a reversible process. By introducing a photo BCF generator, the dissociation of the dimer and the formation of the radical adduct become photocontrollable.

The catenation of a singlet diradical dication and modulation of diradical character by metal coordination.

A singlet bis(triarylamine) diradical dication and its zigzag 1D magnetic chain catenated by silver cations were isolated and characterized by single-crystal X-ray crystallography, EPR spectroscopy, SQUID measurements, cyclic voltammetry, and UV-Vis-NIR absorption spectroscopy in conjunction with DFT calculations. The ΔEOS-T has significantly changed due to the coordination of carbonyls (Lewis base) with Ag+ (Lewis acid), revealing that the diradical character can be modulated by Lewis acid-base coordination and interchain intermolecular coupling interactions.

Cadmium-Based Coordination Polymers from 1D to 3D: Synthesis, Structures, and Photoluminescent and Electrochemiluminescent Properties.

Cadmium-based coordination polymers, namely, {[Cd(HL)(L)] ⋅ HN(Et)3 }n (1), [Cd2 (L)2 (H2 O)5 ]n (2), [Cd(L)(phen)]n (3), [Cd(L)(2,2'-bpy)]n (4), [Cd(L)(4,4'-bpy)]n (5), [Cd(L)(bpp)]n (6), [Cd(L)(dpa)]n (7), {[Cd(L)(dpa)] ⋅ H2 O}n (8) (H2 L=4,4'-((p-tolylazanediyl)bis(methylene))dibenzoic acid, phen=1,10-phenanthroline, 2,2'-bpy=2,2'-bipyridine, 4,4'-bpy=4,4'-bipyridine, bpp=1,3-bis(4-pyridyl)propane, dpa=bis(4-pyridyl)amine) have been synthesized in hydro/solvothermal reactions. 1 is a 4-connect 3D network with an eightfold interpenetrating diamond topology. The 1D ladder chain structure of 2 was composed of the dinuclear [Cd2 (CO2 )4 ] subunit bridged with two L2- ligands. 3 shows a 1D double-chain with a channel formed by edging out the coordination water with the rigid co-ligand phen. Polymer 4 displays a 2D lamellar structure based on superseding the coordination water molecules by the rigid chelating auxiliary ligands 2,2'-bpy. By substituting the small molecules with a rigid bridging ligand 4,4'-bpy, a 2D undulating structure of 5 was built. Compounds 6 and 7 exhibit a 2D layer structure with a 4-connect (44 ⋅ 62 ) sql-net. Compound 8 presents a 3D architecture with a sixfold interpenetrating diamond topology. Through our construction strategy, versatile structures from 1D-3D have been rationally designed by controlling the process condition and rigid/flexible of N-donor spacers. Additionally, the photoluminescence, charge transfer, and electrochemical luminescence (ECL) properties of 1-8 have been demonstrated.