Metal-free photocatalysts with charge-transfer excited states enable visible light-driven atom transfer radical polymerization.

Metal-free donor-acceptor photocatalysts enable efficient O-ATRP under visible light, allowing for precise control over polymer molecular weight with low dispersity. These photocatalysts achieve sufficient reductive potential to drive the reaction in their charge-transfer (CT) excited state. The reported efficient photocatalytic O-ATRP has significant potential in scalable polymer synthesis and photolithography.

Nanorings Resembling Beehives for Ultrasensitive Fluorescence Detection.

In this study, we showcase the fabrication of two nanorings resembling beehives using intricately designed donor-acceptor (D-A) fluorophores. The D-A fluorophores, featuring three twisted fluorene groups on each side of the acceptor group, adopt a bent conformation that promotes the creation of a nanoring morphology upon aggregation. With porosity for maximum binding sites, high emission efficiency, and well-organized arrangements, the nanoring-based hives offer exceptional sensitivity and selectivity in the detection of organic sulfides.

Concentric hollow multi-hexagonal platelets from a small molecule.

The creation of well-defined hollow two-dimensional structures from small organic molecules, particularly those with controlled widths and numbers of segments, remains a formidable challenge. Here we report the fabrication of the well-defined concentric hollow two-dimensional platelets with programmable widths and numbers of segments through constructing a concentric multiblock two-dimensional precursor followed by post-processing. The fabrication of concentric multi-hexagons two-dimensional platelets is realized by the alternative heteroepitaxial growth of two donor-acceptor molecules.

Light-Regulated Nucleation for Growing Highly Uniform Single-Crystalline Microrods.

We report a light-irradiation method to control the synchronous nucleation of a donor-acceptor (D-A) fluorophore for growing highly uniform single-crystalline microrods, which is in sharp contrast to the prevailing methods of restricting spontaneous nucleation and additionally adding seeds. The D-A fluorophore was observed to undergo photoinduced electron transfer to CrCl, leading to the generation of HCl and the subsequent protonation of the D-A fluorophore. By intensifying photoirradiation or prolonging its duration, the concentration of protonated D-A fluorophores can be rapidly increased to a high supersaturation level.

Uniform Colloidal Polymer Rods by Stabilizer-Assisted Liquid-Crystallization-Driven Self-Assembly.

The synthesis of anisotropic colloidal building blocks is essential for their self-assembly into hierarchical materials. Here, a highly efficient stabilizer-assisted liquid-crystallization-driven self-assembly (SA-LCDSA) strategy was developed to achieve monodisperse colloidal polymer rods. This strategy does not require the use of block copolymers, but only homopolymers or random copolymers.

Living Self-Assembly of Metastable and Stable Two-Dimensional Platelets from a Single Small Molecule.

This study reports the design of a donor-acceptor (D-A) molecule with two fluorene units on each side of a benzothiadiazole moiety, which allows multiple intermolecular interactions to compete with one another so as to induce the evolution of the metastable 2D platelets to the stable 2D platelets during the self-assembly of the D-A molecule. Importantly, the living seeded self-assembly of metastable and stable 2D structures with precisely controlled sizes can be conveniently achieved using an appropriate supersaturated level of a solution of the D-A molecule as the seeded growth medium that can temporarily hold the almost-proceeding spontaneous nucleation from competing with the seeded growth. The stable 2D platelets with smaller area sizes exhibit higher sensitivity to gaseous dimethyl sulfide, illustrating that the novel living self-assembly method provides more available functional structures with controlled sizes for practical applications.

Fabrication of Two-Dimensional Platelets with Heat-Resistant Luminescence and Large Two-Photon Absorption Cross Sections via Cooperative Solution/Solid Self-Assembly.

The combination of solution self-assembly, which enables primary morphological control, and solid self-assembly, which enables the creation of novel properties, can lead to the formation of new functional materials that cannot be obtained using either technique alone. Herein, we report a cooperative solution/solid self-assembly strategy to fabricate novel two-dimensional (2D) platelets. Precursor 2D platelets with preorganized packing structure, shape, and size are formed via the living self-assembly of a donor-acceptor fluorophore and volatile coformer (i.

Development of Binary Coassemblies for Sensitively and Selectively Detecting Gaseous Sarin.

The low sensitivity and poor selectivity of fluorescence sensors for real gaseous sarin detection greatly hinder their real-world applications. In this work, we report the development of a novel fluorophore with an active N-H vibration in the benzimidazole group for the sensitive detection of gaseous sarin. We demonstrate that the interactions between the nucleophilic fluorine atom in sarin and the electrophilic hydrogen atom in the benzimidazole group of the fluorophore can restrict the N-H vibration to yield sensitive fluorescence-enhancing responses.

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Fabrication of uniform two-dimensional (2D) structures from small molecules remains a formidable challenge for living self-assembly despite its great success in producing uniform one-dimensional (1D) structures. Here, we report the construction of unprecedented uniform 2D platelets with tailorable shapes and controlled sizes by creating new nuclei from a donor-acceptor (D-A) molecule and 1-hexanol to initiate 2D living self-assembly. We demonstrate that the D-A molecule undergoes 1-hexanol-induced twisting to form continuous alternative hydrogen bonds in-between under electrostatic attraction, which in turn forms a new nucleus.

Rapid Assessment of Meat Freshness by the Differential Sensing of Organic Sulfides Emitted during Spoilage.

In this work, we report the fabrication of a two-member fluorescence sensor array that enables the assessment of three stages (fresh, slightly spoiled, and moderately or severely spoiled) of meat spoilage. The first member of the array, which has strong chalcogen bonding and sulfur-π interactions with organic sulfides, exhibits very high sensitivity, while the second member of the array, which has weak chalcogen bonding and sulfur-π interactions with organic sulfides, exhibits lower sensitivity. On the basis of the combined fluorescence responses of the two members, three stages of meat spoilage, including fresh, slightly spoiled, and moderately or severely spoiled, can be monitored.

Emergent Photostability Synchronization in Coassembled Array Members for the Steady Multiple Discrimination of Explosives.

The design of sensor array members with synchronous fluorescence and photostability is crucial to the reliable performance of sensor arrays in multiple detections and their service life. Herein, a strategy is reported for achieving synchronous fluorescence and photostability on two coassemblies fabricated from carbazole-based energy donor hosts and a photostable energy acceptor. When a small number of the same energy acceptors are embedded into two carbazole-based energy donor hosts, the excitation energy of the donors can be efficiently harvested by the acceptors through long-range exciton migration and Förster resonance energy transfer (FRET) to achieve synchronous fluorescence and photostability in both coassemblies.

Stable organic self-assembled microwire lasers for chemical vapor sensing.

Organic microlasers hold great potentials in fabricating on-chip sensors for integrated photonic circuits due to their chemical versatility and reactivity. However, chemical vapor detection is still challenging for organic microlaser sensors, as it requires not only optical gain and self-assembly capability, but also rapid response to stimuli and long-term stability under high excitation power. In this work, a new laser dye 4,7-bis(9-octyl-7-(4-(octyloxy)phenyl)-9H-carbazol-2-yl)benzo[c][1,2,5]thiadiazole (BPCBT) is designed and synthesized, which self-assembles into microwires showing strong intramolecular charge transfer (ICT) photoluminescence with >80% quantum efficiency.

Highly Photostable and Luminescent Donor-Acceptor Molecules for Ultrasensitive Detection of Sulfur Mustard.

Real-time, high signal intensity, and prolonged detection is challenging because of the rarity of fluorophores with both high photostability and luminescence efficiency. In this work, new donor-acceptor (D-A) molecules for overcoming these limitations are reported. A hybridized local and an intramolecular charge-transfer excited state is demonstrated to afford high photoluminescence efficiency of these D-A molecules in solution (≈100%).

Long-Range Exciton Migration in Coassemblies: Achieving High Photostability without Disrupting the Electron Donation of Fluorene Oligomers.

In this work, photostable coassemblies from a nonphotostable fluorene oligomer (the energy donor) and a photostable oligomer (the energy acceptor) are fabricated. Long-range exciton migration over a net distance of about 370 energy-donor molecules to energy acceptors is demonstrated in such coassemblies. The fast and long energy migration allows harvesting of the excitation energy of energy donors by embedding a small number of energy acceptors for photostability enhancement.

Universal Strategy for Improving the Sensitivity of Detecting Volatile Organic Compounds by Patterned Arrays.

The diffusion of target analytes is a determining factor for the sensitivity of a given gas sensor. Surface adsorption results in a low-concentration region near the sensor surface, producing a concentration gradient perpendicular to the surface, and drives a net flux of molecules toward solid reactive reagents on the sensor surface, that is, vertical diffusion. Here, organic semiconductor supramolecules were patterned into micromeshed arrays to integrate vertical and horizontal diffusion pathways.

Light-Driven Crawling of Molecular Crystals by Phase-Dependent Transient Elastic Lattice Deformation.

The light-driven crawling of a molecular crystal that can form three phases, (α, β, and γ) is presented. Laser irradiation of the molecular crystal can generate phase-dependent transient elastic lattice deformation. The resulting elastic lattice deformation that follows scanning irradiation of a laser can actuate the different phases of molecular crystal to move with different velocity and direction.

Monolayer Two-dimensional Molecular Crystals for an Ultrasensitive OFET-based Chemical Sensor.

The sensitivity of conventional thin-film OFET-based sensors is limited by the diffusion of analytes through bulk films and remains the central challenge in sensing technology. Now, for the first time, an ultrasensitive (sub-ppb level) sensor is reported that exploits n-type monolayer molecular crystals (MMCs) with porous two-dimensional structures. Thanks to monolayer crystal structure of NDI3HU-DTYM2 (NDI) and controlled formation of porous structure, a world-record detection limit of NH (0.

Sensitive Fluorescence Detection of Phthalates by Suppressing the Intramolecular Motion of Nitrophenyl Groups in Porous Crystalline Ribbons.

A novel, highly sensitive fluorescence sensor for phthalates is developed by introducing nitrophenyl groups to a trifluorene molecule that can form porous crystalline ribbons. On the basis of single-crystalline analysis and theoretical calculations, we demonstrate that phthalate molecules can diffuse into the caves of crystalline ribbons and effectively suppress the rotation of nitrophenyl groups via noncovalent interactions to enhance the emission. Because of this novel response mechanism, fluorescence detection of phthalates with high sensitivity (the limit of detection of widely used di(2-ethylhexyl) phthalate (DEHP) is 0.

Emergent Self-Assembly Pathways to Multidimensional Hierarchical Assemblies using a Hetero-Seeding Approach.

The controlled formation of complex and functional 1-, 2-, and 3D hierarchical assemblies from molecular building blocks represents a key current challenge. Herein, we report the use of a seeded growth approach for a series of perylenediimide-based molecules (PDIs 1-4) to access otherwise inaccessible self-assembly pathways that yield complex hierarchical structures. The key to the new approach is to use hetero-seeds which possess a different composition and morphology from that of the molecular building block.

Ultrasensitive Detection of Sulfur Mustard via Differential Noncovalent Interactions.

In this work, we fabricate two types of hierarchical microspheres, i.e., one coassembled from two fluorene-based oligomers (1 and 2) and one self-assembled from a fluorene-based oligomer (1), for ultrasensitive and selective detection of trace sulfur mustard (SM) vapor.

Kinetic Control of a Self-Assembly Pathway towards Hidden Chiral Microcoils.

Manipulating the self-assembly pathway is essentially important in the supramolecular synthesis of organic nano- and microarchitectures. Herein, we design a series of photoisomerizable chiral molecules, and realize precise control over pathway complexity with external light stimuli. The hidden single-handed microcoils, rather than the straight microribbons through spontaneous assembly, are obtained through a kinetically controlled pathway.

Light-Driven Continuous Twist Movements of Microribbons.

Despite many advances in the development of artificial systems with helical twist motions or deformations, obtaining materials that can undergo continuous twist movements upon an energy input remains a great challenge. In this work, a continuous twist movement of microribbons driven by scanning laser irradiation, a process that a twist generates initially at one end of the microribbon and is continuously transmitted to the other end and then kept twisting, is reported. Key factors to the achievement of this movement are the fabrication of elastic microribbons that possess relatively low elastic modulus and diagonal photoinduced π-stacking distortion relative to the microribbon long axis.