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 (AmBn) 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 Rh ∼ M1.13. 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.
On the surface: Adsorption of O(2) at the surface oxygen vacancy (SOV) sites of TiO(2) reconstructs the lattice oxygen (healing SOVs), resulting in a decrease of the photocatalytic activity of oxidizing CO over vacuum-pretreated TiO(2) with increasing temperature (see scheme). Adsorption of H(2) produces new SOVs at the TiO(2) surface and stabilizes the photocatalytic activity. Photocatalytic oxidation of CO over vacuum-pretreated TiO(2) is performed in a series of systems with the introduction of O(2), CO, and H(2) in different orders. The photocatalytic oxidation of CO is dependent on the order of introduction of O(2), CO, or H(2), and introducing O(2) prior to CO promotes the oxidation of CO. Moreover, an increase of reaction temperature suppresses the oxidation of CO, but the preintroduction of H(2) reduces this suppression effect. The results of the chemisorption of O(2), CO, and H(2) at the TiO(2) surface reveal that the adsorbed O(2) heals the surface oxygen vacancy (SOV) sites of TiO(2), while the adsorbed CO and H(2) promote the formation of new SOVs. It is proposed that changes in the amounts of adsorbed O(2) and SOVs are mainly responsible for the differences of CO conversion in different systems.
A series of spiro [fluorene-9,7′-dibenzo[c,h]acridine]-5′-one (SFDBAO) derivatives have been concisely and cleanly obtained by exposure to sunlight without external photosensitizers in the higher yields than that when using a UV lamp. An interesting autocatalyst and self-sensitive procedure have been proposed to explain the effective photooxygenation. SFDBAO derivatives exhibit the continuous π-stacks in single-crystal and electron-withdraw properties with red light-emitting and photovoltaic properties.
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