Single-Photon Emission from Organic Dye Molecules Adsorbed on a Quantum Dot via Energy Transfer.

Single-photon emissions from individual emitters are crucial in fundamental science and quantum information technologies. Multichromophoric systems, comprising multiple dyes, can exhibit single-photon emissions through efficient annihilation between the excited states; however, exploring this phenomenon in complex systems remains a challenge. In this study, we investigated the photon statistics of emissions from multiple perylene bisimide (PBI) dyes adsorbed onto the surface of CdSe/ZnS quantum dots (QDs).

One-Dimensionally Arranged Quantum-Dot Superstructures Guided by a Supramolecular Polymer Template.

Colloidal quantum dots (QDs) exhibit important photophysical properties, such as long-range energy diffusion, miniband formation, and collective photoluminescence, when aggregated into well-defined superstructures, such as three-dimensional (3D) and two-dimensional (2D) superlattices. However, the construction of one-dimensional (1D) QD superstructures, which have a simpler arrangement, is challenging; therefore, the photophysical properties of 1D-arranged QDs have not been studied previously. Herein, we report a versatile strategy to obtain 1D-arranged QDs using a supramolecular polymer (SP) template.

An Unsymmetrical 5,15-Disubstituted Tetrabenzoporphyrin: Effect of Molecular Symmetry on the Packing Structure and Charge Transporting Property.

Molecular design strategy to control the crystal structure of two-dimensional (2D) π-extended organic semiconductors has not been intensively explored. We synthesized an unsymmetric tetrabenzoporphyrin derivative (TIPS-Ph-BP) to demonstrate the effect of molecular symmetry on crystal packing. TIPS-Ph-BP formed an antiparallel slipped π-stacking and 2D herringbone-like structure.

Correlation between Single-Photon Emission and Size of Cesium Lead Bromide Perovskite Nanocrystals.

Emission photon statistics of semiconductor nanocrystal quantum dots (QDs), including lead halide perovskite nanocrystals (PNCs), are important fundamental and practical optical properties. Single QDs exhibit high-probability single-photon emission owing to the efficient Auger recombination between generated excitons. Because the recombination rate depends on QD size, single-photon emission probability should be size-dependent.

A Highly Ordered Quantum Dot Supramolecular Assembly Exhibiting Photoinduced Emission Enhancement.

Multicomponent supramolecular assembly systems enable the generation of materials with outstanding properties, not obtained from single-component systems, via a synergetic effect. Herein, we demonstrate a novel supramolecular coassembly system rendering highly ordered quantum dot (QD) arrangement structures formed via the self-assembly of azobenzene derivatives, where the photocontrollable photoluminescence (PL) properties of the QDs are realized based on photoisomerization. Upon mixing the assembled azobenzene derivatives and QDs in apolar media, a time-evolution coaggregation into hierarchical nanosheets with a highly ordered QD arrangement structure occurs.

Slow Anion-Exchange Reaction of Cesium Lead Halide Perovskite Nanocrystals in Supramolecular Gel Networks.

Cesium lead halide perovskite nanocrystals are widely studied as among the most attractive emissive nanomaterials because of their high photoluminescence quantum yield and tunable emission wavelengths over the whole visible-light region by the halide ion-exchange reaction. However, the reactions were often observed in solution and generally very fast, which interferes with the fine-tuning capability of the emission properties. Here, we report a novel nanocrystal-organogel hybrid soft material in which the perovskite nanocrystals in a supramolecular gel exhibit extremely slow and inhomogeneous anion-exchange reactions that are different from those in solution.

Visible-Light-Induced Heptacene Generation under Ambient Conditions: Utilization of Single-crystal Interior as an Isolated Reaction Site.

The photo-induced generation of unstable molecules generally requires stringent conditions to prevent oxidation and the concomitant decomposition of the products. The visible-light-induced conversion of two heptacene precursors to heptacene was studied. Single crystals of bis- and mono-α-diketone-type heptacene precursors (7-DK2 and 7-DK1, respectively), were prepared to investigate the effect of precursor structure on reactivity.

Self-Assembly of Semiconductor Quantum Dots using Organic Templates.

Colloidal semiconductor nanocrystals, known as quantum dots (QDs), are regarded as brightly photoluminescent nanomaterials possessing outstanding photophysical properties, such as high photodurability and tunable absorption and emission wavelengths. Therefore, QDs have great potential for a wide range of applications, such as in photoluminescent materials, biosensors and photovoltaic devices. Since the development of synthetic methods for accessing high-quality QDs with uniform morphology and size, various types of QDs have been designed and synthesized, and their photophysical properties dispersed in solutions and at the single QD level have been reported in detail.

In Situ Observation of Emission Behavior during Anion-Exchange Reaction of a Cesium Lead Halide Perovskite Nanocrystal at the Single-Nanocrystal Level.

Postsynthesis anion-exchange reaction of cesium lead halide (CsPbX; X = Cl, Br, and I) perovskite nanocrystals (NCs) has emerged as a unique strategy to control band gap. Recently, the partially anion-exchanged CsPb(Br/I) NC was reported to form an inhomogeneously alloyed heterostructure, which could possibly form some emission sites depending on the halide composition in the single NC. In this work, we observed the in situ emission behavior of single CsPb(Br/I) NCs during the anion-exchange reaction.

Systematic Synthesis of Tetrathia[8]circulenes: The Influence of Peripheral Substituents on the Structures and Properties in Solution and Solid States.

We developed the diversity-oriented approach for the synthesis of tetrathia[8]circulenes with a variety of peripheral substituents. Iridium-catalyzed direct C-H borylation of tetrathienylene provided 1,4,7,10-tetraboryltetrathienylene as a major product. 1,4,7,10-Tetraboryltetrathienylene served as an a key intermediate to achieve the selective synthesis of octasubstituted or tetrasubstituted tetrathia[8]circulenes via rhodium-catalyzed annulation with symmetric internal alkynes or sequential Sonogashira-Hagihara coupling and base-promoted intramolecular cyclization.

Crystallization-Induced Emission of Azobenzene Derivatives.

Most azobenzene derivatives are utilized as well-defined photoresponsive materials, but their emission properties have not been of great interest as they are relatively poor. Here, we report crystallization-induced emission (CIE) based on the suppression of the photoisomerization of azobenzene derivatives. Although these molecules show negligible emission in solution, their microcrystals exhibit intense emission from the azobenzene moieties as a result of CIE.

Photoconversion of 6,13-α-diketopentacene single crystals exhibiting light intensity-dependent morphological change.

Recently, we revealed that 6,13-dihydro-6,13-ethanopentacene-15,16-dione (PDK) could be quantitatively photoconverted into pentacene even in the crystal phase, accompanied by the destruction of the crystals. In this work, we investigated the relationship between the photoinduced morphological changes and the light intensity for the photoconversion at a single micrometre-sized crystal level. Photoirradiation with a strong intensity (over 100 kW cm-2) resulted in hole formation in a single crystal.

Colloidal Quantum Dot Arrangement Assisted by Perylene Bisimide Self-Assembly.

Colloidal semiconductor nanocrystals, so-called quantum dots (QDs), are attractive as molecular-like smart nanomaterials, and their emission and optoelectronic properties in the dispersed state have been actively studied. The construction of supramolecular structures composed of multiple QDs, however, is still challenging. Here, a new strategy to form supramolecular QD structures via self-assembly of perylene bisimide (PBI) dyes is demonstrated.

Hydrogen-bonded rosettes comprising π-conjugated systems as building blocks for functional one-dimensional assemblies.

Hydrogen-bonded supermacrocycles (rosettes) are attractive disk-shaped noncovalent synthons for extended functional columnar nanoassemblies. They can serve not only as noncovalent monomer units for supramolecular polymers and discrete oligomers in a dilute solution but also as constituent entities for soft matters such as gels and lyotropic/thermotropic liquid crystals. However, what are the merits of using supramolecular rosettes instead of using expanded π-conjugated covalent molecules? This review covers the self-assembly of photochemically and electrochemically active π-conjugated molecules through the formation of supramolecular rosettes via directional complementary multiple hydrogen-bonding interactions.

Light-induced unfolding and refolding of supramolecular polymer nanofibres.

Unlike classical covalent polymers, one-dimensionally (1D) elongated supramolecular polymers (SPs) can be encoded with high degrees of internal order by the cooperative aggregation of molecular subunits, which endows these SPs with extraordinary properties and functions. However, this internal order has not yet been exploited to generate and dynamically control well-defined higher-order (secondary) conformations of the SP backbone, which may induce functionality that is comparable to protein folding/unfolding. Herein, we report light-induced conformational changes of SPs based on the 1D exotic stacking of hydrogen-bonded azobenzene hexamers.

Supramolecular Polymerization of Supermacrocycles: Effect of Molecular Conformations on Kinetics and Morphology.

Intricately designed π-conjugated molecules containing interactive groups can be used to generate supramolecular polymers with outstanding structural and functional properties. To construct such supramolecular polymers, the non-covalent synthesis of supermacrocyclic monomers from relatively simple molecules represents an attractive strategy, although this has been rarely exploited. Here, we report the supramolecular polymerization of two barbiturate-naphthalene derivatives that circularly hexamerize by hydrogen bonding.

Water-induced helical supramolecular polymerization and gel formation of an alkylene-tethered perylene bisimide dyad.

An alkylene-tethered perylene bisimide (PBI) dyad with hydrophilic substituents forms helical supramolecular polymers that can be visualized by AFM in THF-water mixtures. The supramolecular polymers also form thixotropic gel-like lyotropic mesophases in the mixtures.

Simultaneous SAXS and SANS Analysis for the Detection of Toroidal Supramolecular Polymers Composed of Noncovalent Supermacrocycles in Solution.

Molecular self-assembly primarily occurs in solution. To better understand this process, techniques capable of probing the solvated state are consequently required. Small-angle scattering (SAS) has a proven ability to detect and characterize solutions, but it is rarely applied to more complex assembly shapes.

Self-sorting regioisomers through the hierarchical organization of hydrogen-bonded rosettes.

The self-assembly of two regioisomeric hydrogen-bonding naphthalenes was studied in mixed states in different polarity solvents. The regioisomers co-assemble to form heteromeric rosettes in chloroform. Upon injecting this solution into methylcyclohexane the heteromeric rosettes kinetically form amorphous aggregates, which over time differentiate into thermodynamically stable distinct nanostructures through self-sorting.

Photoreactive helical nanoaggregates exhibiting morphology transition on thermal reconstruction.

The supramolecular design of photochromic molecules has produced various smart molecular assemblies that can switch their structures and/or functions in response to light stimuli. However, most of these assemblies require large structural changes of the photochromic molecules for an efficient conversion of assembled states, which often suppresses the photoreactivity within the self-assemblies. Here we report molecular assemblies, based on a photo-cross-linkable chromophoric dyad, in which a small amount of ultraviolet-generated photochemical product can guide the entire system into different assembly processes.

Design amphiphilic dipolar π-systems for stimuli-responsive luminescent materials using metastable states.

π-Conjugated compounds that exhibit tunable luminescence in the solid state under external mechanical stimuli have potential applications in sensors and imaging devices. However, no rational designs have been proposed that impart these mechano-responsive luminescent properties to π-conjugated compounds. Here we demonstrate a strategy for mechano-responsive luminescent materials by imparting amphiphilic and dipolar characteristics to a luminescent π-conjugated system.

Photocontrol over self-assembled nanostructures of π-π stacked dyes supported by the parallel conformer of diarylethene.

Diarylethenes (DAEs) have rarely been used in the design of photoresponsive supramolecular assemblies with a well-defined morphology transition owing to rather small structural changes upon photoisomerization. A supramolecular design based on the parallel conformation of DAEs enables the construction of photoresponsive dye assemblies that undergo remarkable nanomorphology transitions. The cooperative stacking of perylene bisimide (PBI) dyes was used to stabilize the parallel conformer of DAE through complementary hydrogen bonds.

Facile synthesis of free-standing polymer brush films based on a colorless polydopamine thin layer.

A free-standing polymer brush film with tailored thicknesses based on a colorless polydopamine (PDA) thin layer is prepared and characterized. The surface-initiated atom transfer radical polymerization (ATRP) of 2-hydroxyethyl methacrylate (HEMA) is performed on a PDA layer with thickness of ca. 6 nm, which generated an optically transparent and colorless free-standing PHEMA brush film (1.