Cooperative assembly of binary molecular components into tubular structures for multiple photonic applications

Magnetically controlled assembly: a new approach to organic integrated photonics

Hierarchical self-assembly of organic molecules or assemblies is of great importance for organic photonics to move from fundamental research to integrated and practical applications. Magnetic fields with the advantages of high controllability, non-contact manipulation, and instantaneous response have emerged as an elegant way to prepare organic hierarchical nanostructures. In this perspective, we outline the development history of organic photonic materials and highlight the importance of organic hierarchical nanostructures for a wide range of applications, including microlasers, optical displays, information encoding, sensing, and beyond. Then, we will discuss recent advances in magnetically controlled assembly for creating organic hierarchical nanostructures, with a particular focus on their potential for enabling the development of integrated photonic devices with unprecedented functionality and performance. Finally, we present several perspectives on the further development of magnetically controlled assembly strategies from the perspective of performance optimization and functional design of organic integrated photonics.

Molecular doping of nucleic acids into light emitting crystals driven by multisite-intermolecular interaction

We reveal the fundamental understanding of molecular doping of DNAs into organic semiconducting tris (8-hydroxyquinoline) aluminum (Alq₃) crystals by varying types and numbers of purines and pyrimidines constituting DNA. Electrostatic, hydrogen bonding, and π-π stacking interactions between Alq₃ and DNAs are the major factors affecting the molecular doping. Longer DNAs induce a higher degree of doping due to electrostatic interactions between phosphate backbone and Alq₃. Among four bases, single thymine bases induce the multisite interactions of π-π stacking and hydrogen bonding with single Alq₃, occurring within a probability of 4.37%. In contrast, single adenine bases form multisite interactions, within lower probability (1.93%), with two-neighboring Alq₃. These multisite interactions facilitate the molecular doping into Alq₃ particles compared to cytosines or guanines only forming π-π stacking. Thus, photoluminescence and optical waveguide phenomena of crystals were successfully tailored. This discovery should deepen our fundamental understanding of incorporating DNAs into organic semiconducting crystals.

Color-Tunable Supramolecular Luminescent Materials

Constructing multicolor photoluminescent materials with tunable properties is an attractive research objective on account of their abundant applications in materials science and biomedical engineering. By comparison with covalent synthesis, supramolecular chemistry has provided a more competitive and promising strategy for the production of organic materials and the regulation of their photophysical properties. By taking advantage of dynamic and reversible noncovalent bonding interactions, supramolecular strategies can, not only simplify the design and fabrication of organic materials, but can also endow them with dynamic reversibility and stimuli responsiveness, making it much easier to adjust the superstructures and properties of the materials. Occasionally, it is possible to introduce emergent properties into these materials, which are absent in their precursor compounds, broadening their potential applications. In an attempt to highlight the state-of-the-art noncovalent strategies available for the construction of smart luminescent materials, an overview of color-tunable materials is presented in this Review, with the emphasis being placed on the examples drawn from host-guest complexes, supramolecular assemblies and crystalline materials. The noncovalent synthesis of room-temperature phosphorescent materials and the modulation of their luminescent properties are also described. Finally, future directions and scientific challenges in the emergent field of color-tunable supramolecular emissive materials are discussed.

Covalently bridged pillararene-based oligomers: from construction to applications

Covalently bridged pillararene-based oligomers (CBPOs) are formed by covalent bonding of pillararene monomers, and they play a critical role in expanding the multi-disciplinary application of pillararenes due to their excellent molecular complexing ability, specially designed geometry and multifunctional linking groups. This article provides a comprehensive review of the synthesis and applications of CBPOs. The design and synthetic strategies of a series of CBPOs (dimers, trimers, tetramers and others) are first introduced. Many CBPOs with multi-cavities and unique geometry are very attractive and efficient building blocks for constructing novel smart supramolecular polymers (SPs) with different topological structures through host-guest interactions. We describe the methods of constructing various SPs based on CBPOs in detail. Furthermore, the extensive applications of CBPOs and CBPO-based SPs in recognition and detection of ions and organic small molecules, selective adsorption and separation, artificial light-harvesting systems, catalysis, drug delivery systems, and others are systematically introduced. Finally, the future challenges and perspectives for CBPOs are also highlighted.

Organic superstructure microwires with hierarchical spatial organisation

Rationally designing and precisely constructing the dimensions, configurations and compositions of organic nanomaterials are key issues in material chemistry. Nevertheless, the precise synthesis of organic heterostructure nanomaterials remains challenging owing to the difficulty of manipulating the homogeneous/heterogeneous-nucleation process and the complex epitaxial relationships of combinations of dissimilar materials. Herein, we propose a hierarchical epitaxial-growth approach with the combination of longitudinal and horizontal epitaxial-growth modes for the design and synthesis of a variety of organic superstructure microwires with accurate spatial organisation by regulating the heterogeneous-nucleation crystallisation process. The lattice-matched longitudinal and horizontal epitaxial-growth modes are separately employed to construct the primary organic core/shell and segmented heterostructure microwires. Significantly, these primary organic core/shell and segmented microwires are further applied to construct the core/shell-segmented and segmented-core/shell type’s organic superstructure microwires through the implementation of multiple spatial epitaxial-growth modes. This strategy can be generalised to all organic microwires with tailored multiple substructures, which affords an avenue to manipulate their physical/chemical features for various applications.

Rationally designing and precisely constructing the dimensions, configurations and compositions of organic micro- and nanomaterials are key issues in material chemistry, but remain challenging. Here, the authors realize the fine synthesis of organic superstructure microwires via a hierarchical epitaxial-growth approach.

Organic Semiconductor-DNA Hybrid Assemblies

Organic semiconductors are photonic and electronic materials with high luminescence, quantum efficiency, color tunability, and size-dependent optoelectronic properties. The self-assembly of organic molecules enables the establishment of a fabrication technique for organic micro- and nano-architectures with well-defined shapes, tunable sizes, and defect-free structures. DNAs, a class of biomacromolecules, have recently been used as an engineering material capable of intricate nanoscale structuring while simultaneously storing biological genetic information. Here, the up-to-date research on hybrid materials made from organic semiconductors and DNAs is presented. The trends in photonic and electronic phenomena discovered in DNA-functionalized and DNA-driven organic semiconductor hybrids, comprising small molecules and polymers, are observed. Various hybrid forms of solutions, arrayed chips, nanowires, and crystalline particles are discussed, focusing on the role of DNA in the hybrids. Furthermore, the recent technical advances achieved in the integration of DNAs in light-emitting devices, transistors, waveguides, sensors, and biological assays are presented. DNAs not only serve as a recognizing element in organic-semiconductor-based sensors, but also as an active charge-control material in high-performance optoelectronic devices.

Cocrystal Engineering: A Collaborative Strategy toward Functional Materials

Cocrystal engineering with a noncovalent assembly feature by simple constituent units has inspired great interest and has emerged as an efficient and versatile route to construct functional materials, especially for the fabrication of novel and multifunctional materials, due to the collaborative strategy in the distinct constituent units. Meanwhile, the precise crystal architectures of organic cocrystals, with long-range order as well as free defects, offer the opportunity to unveil the structure-property and charge-transfer-property relationships, which are beneficial to provide some general rules in rational design and choice of functional materials. In this regard, an overview of organic cocrystals in terms of assembly, containing the intermolecular interactions and growth methods, two functionality-related factors including packing structure and charge-transfer nature, and those advanced and novel functionalities, is presented. An outlook of future research directions and challenges for organic cocrystal is also provided.

One-Dimensional Programmable Polymeric Microfiber Waveguide with Optically Reconfigurable Photonic Functions

Programmable materials and reconfigurable photonic components, which can change their physicochemical properties and functionalities upon external stimuli, are a major topic of interest in modern science. However, most conventional reconfigurable photonic components rely heavily on mechanical deformation, restricting their application. Herein, a novel strategy based on a dynamically tunable fluorescence resonance energy transfer process to design and fabricate programmable fluorescent micropatterns within single polymer microfiber is proposed. A set of reconfigurable photonic components (including optical switchable waveguide systems, photonic analogies of diodes and transistors, as well as one-dimensional (1D) optical encoding) can be achieved within a single polymeric waveguide microfiber straightforwardly, in which such photonic components can be written, erased, and rewritten as 1D binary patterns with tailored external optical stimuli. These results might be of great fundamental value for the rational design of novel reconfigurable photonic devices with numerous potential applications in highly integrated optical communication components and optical computing devices.

Organic field-effect optical waveguides

Integrating electronics and photonics is critically important for the realization of high-density and high-speed optoelectronic circuits. However, it remains challenging to achieve this target due to the difficulty of merging many different areas of science and technology. Here, we show an organic integrated optoelectronic device, namely, organic field-effect optical waveguide, integrating field-effect transistor and optical waveguide together. In such device, the propagation of optical waveguide in the active organic semiconductor can be tuned by the third terminal—the gate electrode of transistor, giving a controllable modulation depth as high as 70% and 50% in parallel and perpendicular directions of charge transport versus optical waveguide, respectively. Also, the optical waveguide with different directions can turn the field-effect of the device with the photodependence ratio up to 14800. The successful integration of active field-effect transistor with semiconductor waveguide modulator expands opportunities for creating scalable integration of electronics and photonics in a chip.

Despite recent advances in organic optoelectronics development, integration of electronics and photonics in a chip remains a challenge. Here, the authors demonstrate organic field-effect optical waveguides that control propagating photons by the electric field produced in an organic transistor.

Supramolecular Polymer-Based Fluorescent Microfibers for Switchable Optical Waveguides

We report the switchable optical waveguide microfibers based on fluorescent supramolecular polymer for the first time. The pillar[5]arene-based supramolecular polymeric microfibers were prepared easily from the viscous solution of bispillar[5]arene host (bisP5A) and diphenylanthracene-derived guest (GD). The resulting microfibers  act as an active optical waveguide material with long propagation distance (400 μm) and low optical propagation loss (0.01 dB/μm). When photoresponsive dithienylethene-derived guest (GDTE) was added, the resulting ternary microfibers show switchable optical waveguide by the noninvasive control of UV/vis light with negligible fatigue over four cycles. This convenient preparation method is also applied for the quadruple-hydrogen-bonded fluorescent supramolecular polymeric microfibers which imply good light propagation property with an optical loss coefficient of 0.02 dB/μm.

Molecular cocrystals: design, charge-transfer and optoelectronic functionality

This perspective article primarily focuses on the research work related to optoelectronic properties of organic charge transfer cocrystals.

Unique adjustable UC luminescence pattern and directional radiation of peculiar-shaped NaYF4: Yb3+/Er3+ microcrystal particle

A new design of peculiar-shaped β-NaYF₄: 20% Yb³⁺/2% Er³⁺ hexagonal microcrystal (PSβHM) is proposed and its upconversion (UC) luminescence with adjustable color pattern is studied with near infrared excitation. Flower-like green UC luminescence emission pattern from blooming to withering process and intensive directional red emission are achieved by simply adjusting the focal point position of the excitation light. The mechanism that determines the unique UC luminescence phenomena are investigated systematically. The function of the internal light reflection and waveguide effect with annular microcavity is explored based on the structure characteristic of the hexagonal microplate. The current work may have great significant and potential applications in the development of optoelectronic device, color display, directional light and laser emission of microsystem.

Donor–acceptor single cocrystal of coronene and perylene diimide: molecular self-assembly and charge-transfer photoluminescence

Organic semiconductor molecules, coronene and perylene diimide, form an alternate stacked cocrystal due to the strong donor–acceptor charge transfer interaction.

Synthesis, mechanism and efficient modulation of a fluorescence dye by photochromic pyrazolone with energy transfer in the crystalline state

The emission intensity of DPA can be efficiently switched by fluorescence resonance energy transfer between the energy donor DPA and acceptor 1b.

Highly Fluorescent Nanotubes with Tunable Diameter and Wall Thickness Self-Assembled from Asymmetric Perylene Diimides

Highly fluorescent bilayer-walled and monolayer-walled nanotubes are assembled from elaborately designed asymmetric perylene diimide (PDI) molecules. The diameter of bilayer-walled nanotubes increases with the size of the branched substituents at the meta-position of the phenyl moiety of PDI molecules, whereas that of monolayer-walled nanotubes remains unchanged regardless of the size of branched substituents.

Organic charge-transfer complexes for the selective accommodation of aromatic isomers using anthracene derivatives and TCNQ

Four organic-charge transfer (CT) complexes (Ct1–Ct4) have been reported. Ct1 discerns p-xylene in the presence of a xylene mixture.

Self-assembled organic hexagonal micro-prisms with high second harmonic generation efficiency for photonic devices

Multiwavelength coherent light sources are key components for circuit integration of nanophotonics. Here, we demonstrated highly efficient second harmonic generation (SHG) in single-crystalline hexagonal micro-prisms (HMPs) of 3-methyl-4-methoxy-4'-nitrostilbene (MMONS) prepared via a facile self-assembled method. We found that the SHG conversion efficiency (ηSHG) of MMONS HMPs increases with increasing the prism side length (d). Local electric field |E|(2) calculations suggest that the symmetrical hexagonal prism shape of HMPs supports helically propagating modes. The SHG light produced at one end of HMP can be coupled into whispering-gallery (WG) like optical modes with a coupling efficiency of 50-80% and helically propagates along the length of HMPs toward another end. Based on this unique helical propagation of SHG light, we construct an optical interconnector by placing a single MMONS HMP on the top of a single micro-ribbon of 1,2-diphenyl-2-pyrazoline (DP). These easily fabricated MMONS HMPs can act as a coherent source, which adds a key component to the tool box of organic nano- and micro-structure optoelectronics.

Controlled synthesis of organic nanophotonic materials with specific structures and compositions

Organic nanomaterials have drawn great interest for their potential applications in high-speed miniaturized photonic integration due to their high photoluminescence quantum efficiency, structural processability, ultrafast photoresponse, and excellent property engineering. Based on the rational design on morphological and componential levels, a series of organic nanomaterials have been controllably synthesized in recent years, and their excitonic/photonic behaviors has been fine-tuned to steer the light flow for specific optical applications. This review presents a comprehensive summary of recent breakthroughs in the controlled synthesis of organic nanomaterials with specific structures and compositions, whose tunable photonic properties would provide a novel platform for multifunctional applications. First, we give a general overview of the tailored construction of novel nanostructures with various photonic properties. Then, we summarize the design and controllable synthesis of composite materials for the modulation of their functionalities. Subsequently, special emphasis is put on the fabrication of complex nanostructures towards wide applications in isolated photonic devices. We conclude with our personal viewpoints on the development directions in the novel design and controllable construction of organic nanomaterials for future applications in highly integrated photonic devices and chips.

Organic nanophotonics: from controllable assembly of functional molecules to low-dimensional materials with desired photonic properties

The tutorial review aims to provide an insight into the relationship among opto-functional molecules, controllable assembly, diverse nanostructures and photonic properties, which can further guide the function-oriented design and synthesis of low-dimensional materials for integrated photonic devices.

Recent advances in organic one-dimensional composite materials: design, construction, and photonic elements for information processing

Many recent activities in the use of one-dimensional nanostructures as photonic elements for optical information processing are explained by huge advantages that photonic circuits possess over traditional silicon-based electronic ones in bandwidth, heat dissipation, and resistance to electromagnetic wave interference. Organic materials are a promising candidate to support these optical-related applications, as they combine the properties of plastics with broad spectral tunability, high optical cross-section, easy fabrication, as well as low cost. Their outstanding compatibility allows organic composite structures which are made of two or more kinds of materials combined together, showing great superiority to single-component materials due to the introduced interactions among multiple constituents, such as energy transfer, electron transfer, exciton coupling, etc. The easy processability of organic 1D crystalline heterostructures enables a fine topological control of both composition and geometry, which offsets the intrinsic deficiencies of individual material. At the same time, the strong exciton-photon coupling and exciton-exciton interaction impart the excellent confinement of photons in organic microstructures, thus light can be manipulated according to our intention to realize specific functions. These collective properties indicate a potential utility of organic heterogeneous material for miniaturized photonic circuitry. Herein, focus is given on recent advances of 1D organic crystalline heterostructures, with special emphasis on the novel design, controllable construction, diverse performance, as well as wide applications in isolated photonic elements for integration. It is proposed that the highly coupled, hybrid optical networks would be an important material basis towards the creation of on-chip optical information processing.

A photoconductive charge-transfer crystal with mixed-stacking donor-acceptor heterojunctions within the lattice

A pyrene derivative as the donor and a butyl-viologen as the acceptor were used to construct a novel charge-transfer cocrystal consisting of mixed-stacking structure and having switchable photoconductivity stemming from the donor-acceptor heterojunctions within the lattice.

One-dimensional organic photonic heterostructures: rational construction and spatial engineering of excitonic emission

Organic photonic heterostructures are constructed through a template-free self-assembly method. The host-guest intermolecular interactions play an essential role in the formation of various block orange-blue-orange and blue/green microtubes. The spatial distribution of excitons is engineered to investigate the excitonic behaviors in light propagation along the axial heterostructures. These results offer a new route to the integration of organic photonic building blocks for optical processing applications.

Quinoacridine derivatives with one-dimensional aggregation-induced red emission property

A new series of acceptor-donor-acceptor (A-D-A) type quinoacridine derivatives (1-3) with aggregation-induced red emission properties were designed and synthesized. In these compounds, the electron-withdrawing 2-(3,5-bis(trifluoromethyl)phenyl)acetonitrile groups act as electron-accepting units, while the alkyl-substituted conjugated core acts as electron-donating units. The restriction of intramolecular rotation was responsible for the AIE behavior of compounds 1-3. All compounds were employed as building blocks to fabricate one-dimensional (1-D) organic luminescent nano- or microwires based on reprecipitation or slow evaporation approaches. Morphological transition from zero-dimensional (0-D) hollow nanospheres to 1-D nanotubes has been observed by recording SEM and TEM images of aggregated sates of compound 2 in THF/H(2)O mixtures at different aging time. It was demonstrated that the synthesized compounds with different lengths of alkyl chains displayed different wire formation properties. The single-crystal X-ray analysis of compound 2 provided reasonable explanation for the formation of 1-D nano- or microstructures.