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

Directional self-assembly of organic vertically superposed nanowires

Organic crystal-based superimposed heterostructures with inherent multichannel characteristics demonstrate superior potential for manipulating excitons/photons at the micro/nanoscale for integrated optoelectronics. However, the precise construction of organic superimposed heterostructures with fixed superimposed sites remains challenging because of the random molecular nucleation process. Here, organic vertically superimposed heterostructures (OSHs) with fixed superimposed positions are constructed via semi-wrapped core/shell heterostructures with partially exposed cores, which provide preferential nucleation sites for further molecular epitaxial growth processes. Furthermore, the relative length ratio from 21.7% to 95.3% between interlayers is accurately adjusted by regulating the exposed area of the semi-wrapped core/shell heterostructures. Significantly, these OSHs with anisotropic optical characteristics demonstrate well regulation of excitation position-dependent waveguide behaviors and can function as photonic barcodes for information encryption. This strategy provides a facile approach for controlling the nucleation sites for the controllable preparation of organic heterostructures and advanced applications for integrated optoelectronics.

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.

Dynamic Epitaxial Growth of Organic Heterostructures for Polarized Exciton Conversion

Highly spatial and angular precision in epitaxial-growth process is crucial for constructing organic low-dimensional heterostructures (OLDHs) with the desired substructures, which remains significant challenge owing to the unpredicted location of complex heterogeneous nucleation. Herein, a dynamic epitaxial-growth approach is developed along the tailored longitudinal/horizontal directions to create diverse OLDHs with hierarchical architectures. The controlled morphology evolution of seed crystals from kinetic to thermodynamic species is achieved via incrementally increasing the crystallization time from 0 to 600 s. Accordingly, the kinetic and thermodynamic seed crystals respectively present the specific lattice-matching crystal-planes of (100) and (011), which facilitates the longitudinal epitaxial-growth (LG) process for triblock heterostructures, and the horizontal epitaxial-growth (HG) process for axial-branch heterostructures. The dominant core/shell heterostructures are prepared via both LG and HG processes with a crystallization time of ≈30 s. Significantly, these prepared OLDHs realize the rationally polarized exciton conversion for optical logic gate application through the exciton conversion and photon propagation at the heterojunction. This strategy provides an avenue for the precise synthesis of OLDHs with anisotropy optical characters for integrated optoelectronics.

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.

Lattice-mismatch-free growth of organic heterostructure nanowires from cocrystals to alloys

Organic heterostructure nanowires, such as multiblock, core/shell, branch-like and related compounds, have attracted chemists’ extensive attention because of their novel physicochemical properties. However, owing to the difficulty in solving the lattice mismatch of distinct molecules, the construction of organic heterostructures at large scale remains challenging, which restricts its wide use in future applications. In this work, we define a concept of lattice-mismatch-free for hierarchical self-assembly of organic semiconductor molecules, allowing for the large-scale synthesis of organic heterostructure nanowires composed of the organic alloys and cocrystals. Thus, various types of organic triblock nanowires are prepared in large scale, and the length ratio of different segments of the triblock nanowires can be precisely regulated by changing the stoichiometric ratio of different components. These results pave the way towards fine synthesis of heterostructures in a large scale and facilitate their applications in organic optoelectronics at micro/nanoscale.

The large-scale synthesis of organic heterostructure nanowires is challenging. Here, the authors report the synthesis of organic triblock nanowires via a lattice mismatch-free strategy.

Organic Branched Heterostructures with Optical Interconnects for Photonic Barcodes

Optical interconnects exhibit superior potential in the precise regulation of photon transmission for organic photonic circuits. However, the rational design of well-defined organic heterostructures toward active optoelectronics remains challenging. Herein, we designed organic branched heterostructures (OBHs) with accurate spatial organization for optical interconnection. Notably, the precise regulation of OBHs has been controllably achieved including the trunk morphologies and the branched microwire number. Significantly, these as-prepared OBHs inherently exhibit the multichannel coupling outputs and the excitation position-dependent waveguide characteristics, leading to various outcoupling signals with tunable intensity and emission colors. The optical interconnects are realized due to the occurrence of exciton conversion and photon propagation between branch and trunk at the heterojunction, benefiting the application possibilities of two-dimensional (2D) optical barcodes.

Hierarchical Self-Assembly of Organic Core/Multi-Shell Microwires for Trichromatic White-Light Sources

White-light-emissive organic micro/nanostructures hold exotic potential applications in full-color displays, on-chip wavelength-division multiplexing, and backlights of portable display devices, but are rarely realized in organic core/shell heterostructures. Herein, through regulating the noncovalent interactions between organic semiconductor molecules, a hierarchical self-assembly approach of horizontal epitaxial-growth is demonstrated for the fine synthesis of organic core/mono-shell microwires with multicolor emission (red-green, red-blue, and green-blue) and especially organic core/double-shell microwires with radial red-green-blue (RGB) emission, whose components are dibenzo[g,p]chrysene (DgpC)-based charge-transfer (CT) complexes. In fact, the desired lattice mismatching (≈2%) and the excellent structure compatibility of these CT complexes facilitate the epitaxial-growth process for the facile synthesis of organic core/shell microwires. With the RGB-emissive substructures, these core/double-shell organic microwires are microscale white-light sources (CIE [0.34, 0.36]). Besides, the white-emissive core/double-shell microwires demonstrate the fascinating full-spectrum light transportation from 400 to 700 nm. This work indeed opens up a novel avenue for the accurate construction of organic core/shell heterostructures, which provides an attractive platform for the organic integrated optoelectronics.

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.

Organic micro/nanoscale materials for photonic barcodes

This review summarizes recent advances in micro/nanoscale photonic barcodes based on organic materials from the aspects of diverse optical encoding techniques.

Assessing the Role of Intermolecular Interactions in a Perylene-Based Nanowire Using First-Principles Many-Body Perturbation Theory

We present a first-principles many-body perturbation theory study of the role of intermolecular coupling in the optoelectronic properties of a one-dimensional (1D) π-stacked nanowire composed of perylene-3,4,9,10-tetracarboxylic diimide molecules on a DNA-like backbone. We determine that strong intermolecular electronic coupling results in large bandwidths and low carrier effective masses, suggesting a high-electron mobility material. Additionally, by including the role of finite-temperature phonons on optical absorption via a newly presented approach, we predict that the optical absorption spectrum  is significantly altered from that at zero temperature due to allowed indirect transitions, while the exciton delocalization and binding energy, a measure of intermolecular electronic interactions, remains constant. Overall, our studies indicate that strong intermolecular coupling can dominate the optoelectronic properties of π-conjugated 1D systems even at room temperature.

Epitaxial growth of dual-color-emitting organic heterostructures via binary solvent synergism driven sequential crystallization

The controlled construction of organic heterostructured architectures derived from molecules with similar nucleation thresholds and concentrations has been rare and remains a great challenge. Herein, we report a sequential epitaxial growth to synthesize dual-color-emitting organic heterostructures with 9,10-bis(phenylethynyl)anthracene (BPEA) microwire trunks and tris-(8-hydroxyquinoline)aluminium (Alq3) microstructure branches by an anti-solvent induced sequential crystallization strategy. During the epitaxial growth process, the hydrogen-bonding interactions of the anti-solvent and solvent cause a large change in the solubility and crystallization rate of BPEA and Alq3 molecules in the mixed system, which facilitates sequential crystallization of organic molecule pairs with similar nucleation thresholds and concentrations into desired heterostructures by manipulating the synergism of anti-solvents and solvents. The Förster resonant energy transfer process in heterostructures could be modulated by varying the structure of heterostructures, such as the shape, amount and angles of the branches. The present synthesis strategy provides a unique insight into the detailed formation mechanism of complex organic heterostructures, further guiding the construction of more functional heterostructure materials.

Covert Photonic Barcodes Based on Light Controlled Acidichromism in Organic Dye Doped Whispering-Gallery-Mode Microdisks

Photonic barcodes with a small footprint have demonstrated a great value for multiplexed high-throughput bioassays and tracking systems. Attempts to develop coding technology tend to focus on the generation of featured barcodes both with high coding capacity and accurate recognition. In this work, a strategy to design photonic barcodes is proposed based on whispering-gallery-mode (WGM) modulations in dye-doped microdisk resonant cavities, where each modulated photoluminescence spectrum constitutes the fingerprint of a corresponding microdisk. The WGM-based barcodes can achieve infinite encoding capacity through tuning the dimensions of the microdisks. These photonic barcodes can be well disguised and decoded based on the light controlled proton release and acidichromism of the organic materials, which are essential to fulfill the functions of anti-counterfeiting, information security, and so on. The results will pave an avenue to new types of flexible WGM-based components for optical data recording and security labels.

Ultralarge Bending Strain and Fracture-Resistance Investigation of Tungsten Carbide Nanowires

Hard tungsten carbide (WC) with brittle behavior is frequently applied for mechanical purposes. Here, ultralarge elastic bending deformation is reported in defect-rare WC [0001] nanowires; the tested bending strain reaches a maximum of 20% ± 3.33%, which challenges the traditional understanding of this material. The lattice analysis indicates that the dislocations are confined to the inner part of the WC nanowires. First, the high Peierls-Nabarro barrier hinders the movement of the locally formed dislocations, which causes rapid dislocation aggregation and hinders long-range glide, resulting in a dense distribution of the dislocation network. In this case, the loading is dispersed along multiple points, which is then balanced by the complex internal mechanical field. In the compressive part, the possible dislocations predominantly emerge in the (0001) plane and mainly slip along the axial direction. The disordered shell first forms at the tensile side and prevents the generation of nanocracks at the surface. The novel lattice kinetics make WC nanowires capable of substantial bending strain resistance. Analytical results of the force-displacement (F-d) curves based on the double-clamped beam model exhibit an obvious nonlinear elastic characteristic, which originates fundamentally from the lattice anharmonicity under moderate stress.

Polymorph-Dependent Electrogenerated Chemiluminescence of Low-Dimensional Organic Semiconductor Structures for Sensing

A sensitive electrogenerated chemiluminescence (ECL) sensor with an organic semiconductor as active material for detecting trace amounts of molecules has been highly desired. However, the crystal structure responses of the ECL properties of the organic semiconductor materials, that is, structure-property relationship, is not clear, which limits the development of the sensitive ECL sensors. Herein, for the first time, we reported a novel concept for molecular-stacking-arrangement-dependent electrogenerated chemiluminescence properties of organic semiconductor rubrene microstructures. The rubrene 1D microwires and 2D hexagonal plates with different polymorphs (triclinic and monoclinic) were controllably constructed with the reprecipitation method. The supersaturation of the rubrene molecules plays an important role in the thermodynamically and kinetically dominated process of growth, which affects not only the polymorphs but also the morphology of the obtained microstructures. These microstructures show good optoelectronic properties, which are used as active ECL materials for the construction of ECL sensors. The ECL sensors exhibited distinct electrogenerated chemiluminescence properties, probably related to different inherent crystal-structure-dependent triplet-triplet annihilation rate and charge-transfer rate. The sensors manifested electrogenerated chemiluminescence responses in broad linear range for the monitoring of creatinine molecules.

Synthesis of a Tetraphenylethene-Substituted Tetrapyridinium Salt with Multifunctionality: Mechanochromism, Cancer Cell Imaging, and DNA Marking

The development of functional materials is a crucial step in the development of newer and better technologies. The development of efficient luminescent materials, whose potential lie in applications in fields such as electronics, optics, data storage, and biological sciences, through simple synthetic procedures is therefore of interest. Herein, we report the synthesis of a tetrapyridinium-tetraphenylethylene (TPy-TPE) luminogen with multiple functionalities. TPy-TPE displayed characteristic features of an aggregation-induced emission material being weakly emissive in solution, but strongly emissive when aggregated and in the solid state. The solid-state emission of TPy-TPE can be reversibly switched between green and yellow by grinding–fuming/heating processes with a high contrast due to a transformation from a crystalline to an amorphous state and vice versa. TPy-TPE also works as a good fluorescent visualiser for specific staining for cellular imaging and as a DNA marker.

Organic nanophotonic materials: the relationship between excited-state processes and photonic performances

Organic active nanophotonics: excited-state coupled photonic behaviours strongly determine the optical performances of organic nanomaterials. The photonic actions and related material properties can be well controlled by tailoring the intra/inter-molecular excited-state processes.

A Novel Mechanochromic and Photochromic Polymer Film: When Rhodamine Joins Polyurethane

A rhodamine-based molecule, Rh-OH, is synthesized. Rh-OH exhibits a reversible mechanochromic luminescent character but a passivating response to UV light. An elastomeric polymer film based on polyurethane with embedded Rh-OH is prepared via a polycondensation reaction. The film shows mechanochromic and photochromic properties with reversible color change, which originates from the isomerization of the Rh-OH molecule from a twisted spirolactam in the ring-closed form to a planarized zwitterionic structure in the ring-open state.

"H"-like Organic Nanowire Heterojunctions Constructed from Cooperative Molecular Assembly for Photonic Applications

"H"-like organic nanowire heterojunctions with two parallel 2-acetyl-6-dimethylamino-naphthalene wires vertically bridged by one 2,4,5-triphenylimidazole wire are prepared via cooperative molecular assembly in liquid phase. The exciton conversion at the junction interfaces is beneficial for the design of multichannel light-controlled photo-switches. The results provide better understanding of molecular assembly toward specific structures and open up new prospects for the creation of novel photonic materials.

1,8-Bis(phenylethynyl)anthracene – gas and solid phase structures

The structure of 1,8-bis(phenylethynyl)anthracene has been studied in detail in the gas phase and the solid state by a combined GED/MS method and by XRD of a single crystal. Aryl⋯aryl interactions are discussed in terms of dispersive forces.

Si-doped ceramic Al4O4C nanowires: full-color emission and optical waveguide behavior

The increasing prosperity of the photonics field has hastened the development of several sub-disciplines, with the aim to create advanced photonic devices, produce photonic circuits and eventually enable all-optical communication. This development has resulted in the demand for micro-nano-sized functional units with specific space dimensions (1D & 2D) for subwavelength photon operation purposes. The fundamental task involves a search for available semiconductor materials as micro-nano light sources and optical interconnections; in this regard, finding a white-light source is the most challenging task because typical band-band emission is not possible in the single phase. Using current approaches, which rely on surface-state emission and the integration of various emission components, it is impossible to achieve single-phase, single-unit components with specific space dimensions. Here, we achieved continuous full-color (ultraviolet to red) emission by engineering a single Al₄O₄C nanowire with Si doping, which created impurity levels in the bandgap and conduction band. High light propagation performance was also observed when blue, green and red lasers were coupled into a single nanowire using a tapered optical fiber. This novel 1D nanostructure is an excellent candidate for use in future photonic circuits as a white-light source or interconnection component.

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.

Epitaxial self-assembly of binary molecular components into branched nanowire heterostructures for photonic applications

We report a sequential epitaxial growth to prepare organic branched nanowire heterostructures (BNwHs) consisting of a microribbon trunk of 1,4-dimethoxy-2,5-di[4'-(cyano)styryl]benzene (COPV) with multiple nanowire branches of 2,4,5-triphenylimidazole (TPI) in a one-pot solution synthesis. The synthesis involves a seeded-growth process, where COPV microribbons are grown first as a trunk followed by a seeded-growth of TPI nanowire branches at the pregrown trunk surfaces. Selected area electron diffraction characterizations reveal that multiple hydrogen-bonding interactions between TPI and COPV components play an essential role in the epitaxial growth as a result of the structural matching between COPV and TPI crystals. A multichannel optical router was successfully realized on the basis of the passive waveguides of COPV green photoluminescence (PL) along TPI nanowire branches in a single organic BNwH.

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.

Multicolour laser from a single bandgap-graded CdSSe alloy nanoribbon

Multicolour lasing with wavelength varying from 578 nm to 640 nm is realized from a single bandgap-graded CdSSe alloy nanoribbon, by selecting the excited spot at room temperature. Though reabsorption is a serious problem to achieve lasing at short wavelength, multiple scatters on the nanoribbon form localized cavities, and thus lasing at different wavelengths is realized. By increasing the excitation area, multicolour lasing from the same nanoribbon is also observed simultaneously.

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.

Manipulation of light flows in organic color-graded microstructures towards integrated photonic heterojunction devices

Organic color-graded optical waveguides permit low-power photonic analogies of diode/transistors based on the energy-transferred conversion of exciton species. The donor-acceptor junction can asymmetrically output blue/red colors due to the mono-directional energy transfer during light propagation. The switching function of transistors is achieved with an additional gate input by altering the ground state density of acceptors. These organic heterogeneous waveguides are further cascaded together to steer the guided light flows for potential applications in photonic integrations.