Three-Dimensional Zinc(II) and Cadmium(II) Coordination Frameworks with <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′‑Tetrakis(pyridin-4-yl)methanediamine: Structure, Photoluminescence, and Catalysis

Coordination polymer networks, i.e., [Zn­(tpmd)­(H₂O)]­(NO₃)₂·7H₂O (<b>1</b>) and [Cd­(tpmd)­(H₂O)₂]­(NO₃)₂·4H₂O·4CH₃OH (<b>2</b>), were assembled from M^II(NO₃)₂ hydrates (M = Zn, Cd) and <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetrakis­(pyridin-4-yl)­methanediamine (tpmd) in CH₃OH and characterized. <b>1</b> and <b>2</b> feature three-dimensional networks formed by coordination of the metal ions to the tpmd ligands. <b>1</b> exhibits a strong blue emission at ∼397 nm, while <b>2</b> shows strong emission at ∼361 nm. <b>1</b> is a more efficient catalyst for the transesterification of various esters than <b>2</b>

Rigidity-Induced Delayed Fluorescence by Ortho Donor-Appended Triarylboron Compounds: Record-High Efficiency in Pure Blue Fluorescent Organic Light-Emitting Diodes

A synthetic approach to highly efficient thermally activated delayed fluorescence (TADF) is proposed that uses ortho donor (D)–acceptor (A) compounds (PXZ<i>o</i>B, DPA<i>o</i>B, and Cz<i>o</i>B), wherein the acceptor is based on triarylboron and the donor is phenoxazine (PXZ), diphenylamine (DPA), or carbazole (Cz). Combined with the ortho D–A connectivity, the bulky nature of the triarylboron endows the D–A dyads with inherent steric “locking” for a highly twisted arrangement, leading to a small energy difference between singlet and triplet excited states (Δ<i>E</i>_ST) and thus exhibiting very efficient TADF with microsecond-range lifetimes. In sharp contrast, the corresponding para D–A derivatives, DPA<i>p</i>B and Cz<i>p</i>B, only display short-lived, normal fluorescence. Organic light-emitting diodes (OLEDs) incorporating the proposed ortho D–A compounds as emitters display orange, greenish-blue, and pure blue emission and exhibit high external quantum efficiency (η_EQE). In particular, the pure blue OLEDs based on the proposed ortho D–A emitters with a carbazole donor (Cz<i>o</i>B) show a record-high η_EQE of 22.6% with CIE color coordinates of (0.139, 0.150), well illustrating the validity of the proposed approach. Upon optical optimization, the η_EQE is further improved to 24.1%

Asymmetric Restriction of Intramolecular Rotation in Chiral Solvents

Commercially available molecular rotor (MR) compounds were recrystallized using chiral monoterpenes as solvents. The resulting crystals exhibited large circular dichroism signals with opposing signs according to the handedness of the chiral solvent used. X-ray crystallographic analysis showed that the chirality originated from asymmetric restriction of intramolecular rotation in the crystals. The crystals were also highly emissive due to restricted bond rotation, while solutions of the materials were almost nonemissive. The solvent-to-MR chirality transfer approach to crystallization discussed herein should be a convenient, universal way to obtain highly emissive chiral crystals

Diterpenoids from the Roots of <i>Euphorbia fischeriana</i> with Inhibitory Effects on Nitric Oxide Production

Bioactivity-guided isolation of a methanolic extract of <i>Euphorbia fischeriana</i> led to the isolation of four new abietane-type diterpenoids, fischeriolides A–D (<b>1</b>–<b>4</b>), together with 11 known diterpenoids. Their structures were elucidated based on the interpretation of 1D and 2D NMR spectroscopic and HRESIMS data. The absolute configuration of compound <b>3</b> was determined by single-crystal X-ray diffraction analysis and electronic circular dichroism methods. Compounds <b>5</b>–<b>9</b> exhibited inhibitory effects on LPS-induced nitric oxide production in RAW 264.7 macrophages with IC₅₀ values in the range 4.9–12.6 μM