We report a 2D layered metal-organic framework (MOF) with wide channels named NUS-1 and its activated analogue NUS-1a composed of Zn4O-like secondary building units and tetraphenylethene (TPE)-based ligand 4,4'-(2,2-diphenylethene-1,1-diyl)dibenzoic acid. Due to its special structure, NUS-1a exhibits unprecedented gas sorption behavior, glass-transition-like phase transition under cryogenic conditions, and responsive turn-on fluorescence to various volatile organic compounds. Our approach using angular ligand containing partially fixed TPE units paves a way toward highly porous MOFs with fluorescence turn-on response that will find wide applications in chemical sensing.

We report the synthesis and remarkable properties of the phosphine P(NIiPr) (NIiPr=1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidenamino), a crystalline solid accessible through a short and scalable route. Evaluation of the electron-donor properties reveals a Tolman electronic parameter (TEP) value of 2029.7 cm for the new phosphine that is significantly lower than those of all known phosphines or even N-heterocyclic carbenes. Moreover, P(NIiPr) is more basic [pK (MeCN)=38.8] than Verkade's proazaphosphatranes, thus being the strongest reported nonionic phosphorus(III) superbase. The coordination chemistry of the new phosphine towards different metal centers has been explored, and due to its unique electron-releasing character, the phosphine is capable of capturing and cleaving the CO molecule.

Two tetraphenylethylene (TPE) bridged tetraimidazolium salts, [H L-Et](PF ) and [H L-Bu](PF ) , were used as precursors for the synthesis of the dinuclear Ag and Au tetracarbene complexes [Ag (L-Et)](PF ) , [Ag (L-Bu)](PF ) , [Au (L-Et)](PF ) , and [Au (L-Bu)](PF ) . The tetraimidazolium salts show almost no fluorescence (Φ <1 %) in dilute solution while their NHC complexes display fluorescence "turn-on" (Φ up to 47 %). This can be ascribed to rigidification mediated by the restriction of intramolecular rotation within the TPE moiety upon complexation. DFT calculations confirm that the metals are not involved in the lowest excited singlet and triplet states, thus explaining the lack of phosphorescence and fast intersystem crossing as a result of heavy atom effects. The rigidification upon complexation for fluorescence turn-on constitutes an alternative to the known aggregation-induced emission (AIE).

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