Proton Effects on Diazafluorene Derivatives with Sulfur-Rich Substituents, a Structural, Spectroscopic and Theoretical Study

Multi-site isomerization of synergistically regulated stimuli-responsive AIE materials toward multi-level decryption

Stimuli-responsive aggregation-induced emission (AIE) materials are highly sensitive and rapidly responsive to external signals, making them ideal solid materials for anti-counterfeiting encryption. However, the limited conformational and packing variations resulting from regio-isomerization with a single substituent restricts the stimuli-responsive behavior of these materials. In this work, several AIE-active regio-structural isomers based on the salicylaldehyde Schiff base scaffold have been straightforwardly obtained through multiple substitutions with bromide and triphenylamine moieties. Solvent-effect experiments demonstrate their different orders of charge-transfer and excited-state intramolecular proton transfer upon photoexcitation, indicating the regulation of excited-state processes via multi-site isomerization. These isomers also demonstrate mechanochromism and acidichromism, allowing for adjustable stimuli-responsive effects. As a demonstration, p-Br-TPA with both mechanochromism and acidichromism can be synergistically utilized for multi-level decryption. This study successfully regulates the evolution of excited states through multi-site isomerization, offering a general approach for achieving tunable stimuli-responsive properties in AIE-active salicylaldehyde Schiff bases toward multi-level decryption.

Stereoselective gridization and polygridization with centrosymmetric molecular packing

The gridarenes, with well-defined edges and vertices, represent versatile nanoscale building blocks for the installation of frameworks and architectures but suffer from difficulty in stereoselective control during their synthesis. Here we report a diastereoselective gridization of superelectrophilic diazafluorene-containing substrates (A_mB_n) with crescent shapes into Drawing Hands grids (DHGs). The meso-selectivity reaches 75.6% diastereomeric excess (de) during the gridization of A₁B₁-type substrates and maintains ~80% de during the polygridization of A₂B₂-type monomers. Such stereocontrol originates from the centrosymmetric molecular packing of two charge-delocalized superelectrophiles with synergistically π–π stacking attractions and coulombic repulsions. As meso-stereoregular structures show 20∼30 nm in length, the rigid ring/chain-alternating polygrids have a Mark–Houwink exponent of 1.651 and a molecular weight (M) dependence of the hydrodynamic radius R_h ∼ M^1.13. Via the simulation of chain collapse, meso-configured polygridarenes still adopt rod-like conformations that facilitate the high rigidity of organic nanopolymers, distinguished from toroid backbones of rac-type polygrids.

Gridarenes with well-defined edges and vertices represent versatile nanoscale building blocks for installating frameworks but suffer from lack of stereoselective control during their synthesis. Here, the authors report a diastereoselective gridization of superelectrophilic diazafluorene-containing substrates with crescent shapes into Drawing Hands grids (DHGs).

Carbon Cationic Relay via Superelectrophiles: Synthesis of Spiro-diazafluorenes

Superelectrophilic-initiated carbon cationic relay reactions of diazafluorenones with phenols were developed to provide strategically novel and atom-economic access to spirodiazafluorenes via tandem Friedel-Crafts reaction, nucleophilic addition, and intramolecular cyclization sequences. A range of spirodiazafluorenes that are difficult to synthesize with traditional protocols has been constructed successfully in middle to high yields using this method.

Metal centered oxidation or ligand centered oxidation of metal dithiolene? Spectral, electrochemical and structural studies on a nickel-4-pyridine-1,2-dithiolate system

The complex Et(4)N[Ni(4-pedt)(2)] (1) (4-pedt = 1-(pyridine-4-yl) ethylene-1,2-dithiolate) was synthesized to investigate the behaviour of metal dithiolene compounds upon protonation and oxidation by absorption spectroscopy, electrochemistry and structural analyses and to further understand the electronic states of the dithiolene compounds. It is unexpected that the 915 nm NIR transition band is not shifted when H(+) is added, and it is only affected (blue-shifted) when the compound is oxidized. All the evidence of electronic spectra indicates that the NIR band is relevant to the central [Ni(edt)(2)] moiety (edt = ethylenedithiolate), not the behaviour of individual Ni ions or ligands. It is also not the band of intermolecular interaction of a dimer. The moderately intense band appearing at 655 nm upon protonation is assigned to the intramolecular charge-transfer band between the [Ni(edt)(2)] moiety and the pyridine. The redox potentials of the metal dithiolene are sensitive to the protonation of the pyridyl group. The structures of monocationic complex and the protonated compounds [Ni(4-Hpedt)(2)]·ClO(4)·H(2)O (2) and [Ni(4-Hpedt)(2)]·PhSO(3)·2DMF (3) were characterized by single crystal X-ray determination. The structural data demonstrate that the oxidation of the monoanionic dithiolene complex to neutral does not change the Ni-S bond distances obviously, which further indicates that the process is not only the metal centered oxidation.