Increasing the interlayer distance in layered microribbons enhances the electrically driven twisting response

We designed a class of layered microribbons self-assembled from perylene diimide (PDI) molecules that exhibited a fast electrically driven twisting response. By increasing the length of the side chains of the PDIs, the microribbons maintained the same intralayer molecular orientation but exhibited enlarged interlayer distances, and the elasticity moduli of the resulting layered microribbons were effectively reduced from similar to 1.5 GPa to similar to 75 MPa. The electrically driven twisting response of the microribbons was inversely proportional to the elasticity modulus, indicating that the electroresponse of the resulting materials can be controlled through the interlayer distance. Furthermore, we demonstrated that the influence of the elastic modulus of the microribbons on the electrically driven twisting follows a screw dislocation mechanism. Our work provides a way to design and develop soft materials with a fast mechanical response to external stimuli

Unraveling the Photocatalytic Mechanisms on TiO2 Surfaces Using the Oxygen-18 Isotopic Label Technique

During the last several decades TiO2 photocatalytic oxidation using the molecular oxygen in air has emerged as a promising method for the degradation of recalcitrant organic pollutants and selective transformations of valuable organic chemicals. Despite extensive studies, the mechanisms of these photocatalytic reactions are still poorly understood due to their complexity. In this review, we will highlight how the oxygen-18 isotope labeling technique can be a powerful tool to elucidate complicated photocatalytic mechanisms taking place on the TiO2 surface. To this end, the application of the oxygen-18 isotopic-labeling method to three representative photocatalytic reactions is discussed: (1) the photocatalytic hydroxylation of aromatics; (2) oxidative cleavage of aryl rings on the TiO2 surface; and (3) photocatalytic decarboxylation of saturated carboxylic acids. The results show that the oxygen atoms of molecular oxygen can incorporate into the corresponding products in aqueous solution in all three of these reactions, but the detailed incorporation pathways are completely different in each case. For the hydroxylation process, the O atom in O2 is shown to be incorporated through activation of O2 by conduction band electrons. In the cleavage of aryl rings, O atoms are inserted into the aryl ring through the site-dependent coordination of reactants on the TiO2 surface. A new pathway for the decarboxylation of saturated carboxylic acids with pyruvic acid as an intermediate is identified, and the O2 is incorporated into the products through the further oxidation of pyruvic acid by active species from the activation of O2 by conduction band electrons

Molecular Interactions Control Quantum Chain Reactions toward Distinct Photoresponsive Properties of Molecular Crystals

In this work, we fabricated four diphenylcyclopropenone (DPCP) crystals, which involved various molecular interactions encoded in individual molecular structures 1-4. On the basis of crystalline structural analysis and photoresponsive characterization of the resultant single-crystal microribbons 1-4, we demonstrated that the magnitude of molecular interactions could effectively control the quantum chain reaction and the photoresponsive property of the DPCP crystals. The microribbons 1 and 2 having weak molecular interactions exhibited an efficient chain reaction and large mechanical photoresponses (i.e., photomelting and photodeforming), whereas the microribbons 3 and 4 with strong molecular interactions exhibited no chain reaction and mechanical morphology change. Our work presented a new way to achieve molecular crystals with enhanced mechanical photoresponses

Ortho-Dihydroxyl-9,10-anthraquinone dyes as visible-light sensitizers that exhibit a high turnover number for hydrogen evolution

Pt/TiO2 sensitized by the cheap and organic ortho-dihydroxyl-9,10-anthraquinone dyes, such as Alizarin and Alizarin Red, achieved a TON of approximately 10 000 (TOF > 250 h−1 for the first ten hours) during >80 hours of visible light irradiation (>420 nm) for photocatalytic hydrogen evolution when triethanolamine was used as the sacrificial donor. The stability and activity enhancements can be attributed to the two highly serviceable redox reactions involving the 9,10-dicarbonyl and ortho-dihydroxyl groups of the anthracene ring, respectivel

Fluorescence Detection of a Broad Class of Explosives with One Zinc(II)-Coordination Nanofiber

In this work, we report the development of one fluorescent carbazole-based oligomer <b>1</b>-zinc­(II) coordination nanofiber which enabled the detection of five classes of explosives, i.e., nitroaromatics (dinitrotoluene, DNT, and trinitrotoluene, TNT), aliphatic nitro-organics (2,3-dimethyl-2,3-dinitrobutane, DMNB), nitramines (cyclotrimethylenetrinitramine, RDX), nitro-esters (pentaerythritol tetranitrate, PETN), and black powder (sulfur). We demonstrate that the coordination of zinc ion with a carbazole-based oligomer <b>1</b> allows the formation of the Lewis acid–base complex between explosives and the nanofiber that enhances the electron-accepting ability of the nitro-based explosives and the binding interactions between the sensing nanofibers and explosives. Furthermore, the resulting nanofiber-based sensor exhibited highly sensitive fluorescence quenching when exposed to trace sulfur, thereby enabling the sensitive detection of black powder. Herein, we present a new fluorescent sensor for five classes of explosives, which represents an important advance toward a richer identification of threats

Discrimination of Five Classes of Explosives by a Fluorescence Array Sensor Composed of Two Tricarbazole-Nanostructures

In this work, we report a two-member fluorescence array sensor for the effective discrimination of five classes of explosives. This smallest array sensor is composed of tricarbazole-based nanofibers (sensor member <b>1</b>) and nanoribbons (sensor member <b>2</b>) deposited as two film bands in a quartz tube. On the basis of a simple comparison of the resulting fluorescence quenching ratios between two sensor members and the response reversibility upon exposure to vaporized explosives, five classes of explosives can be sensitively detected and easily discriminated. This array sensor that has only two sensor members and no complex data analysis represents a new design way for discrimination of a broad class of explosives

Corannulene-Based Coordination Cage with Helical Bias

We report here the first corannulene-based molecular cage, constructed via metal-induced self-assembly of corannulene-based ligands. In sharp contrast to those assembled via the planar π-conjugated analogues of corannulene, at ambient and elevated temperatures, the molecular cage exists as an ensemble of four stereoisomers (two pairs of enantiomers), all of which possess a <i>D</i>₅-symmetric (regardless of the counteranions) and inherently helical structure. Decreasing the temperature shifts the equilibrium between different pairs of enantiomers. At low temperature, only one pair of enantiomers is present. Helical bias for the cage could be efficiently achieved by inducing asymmetry with enantiopure anions. When nonenantiopure anions are used, the asymmetry induction abides by the “majority rule”, i.e., the major enantiomer of the chiral anions controls the bias of helical sense of the cages