Controllable and Low-Loss Electrochemiluminescence Waveguide Supported by a Micropipette Electrode

One-dimensional molecular crystal waveguide (MCW) can transmit self-generated electrochemiluminescence (ECL), but heavy optical loss occurs because of the small difference in the refractive index between the crystal and its surroundings. Herein, we report a micropipette electrode-supported MCW (MPE/MCW) for precisely controlling the far-field transmission of ECL in air with a low optical loss. ECL is generated from one terminal of the MCW positioned inside the MPE, which is transmitted along the MCW to the other terminal in air. In comparison with conventional waveguides on solid substrates or in solutions, the MPE/MCW is propitious to the total internal reflection of light at the MCW/air interface, thus confining the ECL efficiently in MCW and improving the waveguide performance with an extremely low-loss coefficient of 4.49 × 10-3 dB μm-1. Moreover, by regulation of the gas atmosphere, active and passive waveguides can be resolved simultaneously inside MPE and in air. This MPE/MCW offers a unique advantage of spatially controlling and separating ECL signal readout from its generation, thus holding great promise in biosensing without or with less electrical/chemical disturbance.

Bio-Photonic Waveguide of a DNA-Hybrid Semiconductor Prismatic Hexagon

A successful identification of DNA-DNA recognition, based on the waveguide effect of a 1D hybrid prismatic hexagon crystal interfacing of DNA with an organic semiconductor is achieved. This bio-hybrid 1D crystal simultaneously discerns the complementary case at its one end against a 1-mer mismatch in 27-mer nucleic acid sequence at the other end. The loss coefficient value of this waveguide is estimated to be 0.159 µm^-1 for the perfect match, which is a stark discrepancy compared to 0.244 µm^-1 for the 1-mer mismatch, implying waveguide performance with a higher efficiency. These results demonstrate successfully that multiple biological interactions can be realized by the optical waveguide of the single 1D bio-hybrid-crystal and will push this class of materials into bio-related applications.

Fine Fabrication and Optical Waveguide Characteristics of Hexagonal tris(8-hydroxyquinoline)aluminum(Ⅲ) (Alq3) Crystal

Herein, we reported on the precise growth and optical waveguide characteristics of hexagonal tris(8-hydroxyquinoline)aluminum(Ⅲ) (Alq3) micro-crystals (MCs). The hexagonal Alq3 MCs were prepared using surfactant-assisted assembly growth with the help of cetyltrimethylammoniumbromide (CTAB), in which the crystallization occurred as a result of molecular assembly and packing. Also, we adjusted the molar ratio of Alq3 and CTAB for the control degree of crystallization. The formation and structure of Alq3 MCs were investigated using field-emission scanning electron microscopy and X-ray diffraction pattern experiments, respectively. The solid-state laser confocal microscope-photoluminescence spectra and charge-coupled device images for the Alq3 MCs were measured to study the luminescence efficiency and colors, respectively. The optical waveguide performance of the hexagonal Alq3 MCs was measured for each side direction. According to our results, crystalline Alq3 micro-crystals are promising materials for application to the development of optical communication devices.

Ultra-long distance carrier transportation in bandgap-graded CdSxSe1-x nanowire waveguides

Carrier transportation in semiconductor nanowires is essential for their application in integrated opto-electronic devices. Therefore, it is of importance to manipulate and enhance the transportation performance of nanowires through micro-nano scale engineering. In this work, the carrier dynamics of the waveguides in the bandgap-graded CdSxSe1-x nanowires is systematically investigated. By developing a spatially separated time-resolved photoluminescence spectroscopy system, the dependence between the propagation distance/direction and the dynamics of the bandgap gradient driven long-range carrier transportation of the nanowires is characterized. In the meantime, the dynamics of carrier concentration driven spontaneous diffusion is also characterized to be compared to. It is found that the continuous carrier transportation which is driven by the bandgap gradient is the dominant process in the active waveguide, where the maximum transportation distance of 100 μm is detected. Such a transportation distance is up to ∼8-fold larger than the spontaneous carrier diffusion distance in the bandgap-graded CdSxSe1-x nanowires. The ultra-long carrier transportation capability in the bandgap gradient nanowires makes them ideal structures for applications in long-distance photo-energy delivery and micro-nanoscale opto-electronics.

Controllably realizing elastic/plastic bending based on a room-temperature phosphorescent waveguiding organic crystal

The room-temperature phosphorescent DBBZL crystals could exhibit reversible bending and irreversible bending based on one crystal. These flexible crystals exhibit good waveguiding property in straight state, elastic bending state and plastic bending state, demonstrating the application of flexibility.

Recently, the study of flexible (elastically bendable and plastically bendable) organic single crystals has become a hot research field in crystal engineering. In general, crystal elasticity and plasticity are incompatible with each other. Different from the applications of fluorescent crystals, the applications of room-temperature phosphorescence (RTP) materials generally ignore the crystallographic nature of large single crystals. Herein, we creatively combine elasticity and plasticity based on one RTP crystal 4,4′-dibromobenzil DBBZL. The in-depth study of the irreversible transformation between elastic bending and plastic bending provided important insights into the mechanism of both elastically bendable crystals and plastically bendable crystals in crystal engineering. The DBBZL crystal exhibits elastic bending (reversible) under external stress, whereas it shows plastic bending (irreversible) after excessive bending. Notably, the first phosphorescent optical waveguides of large single RTP crystals are realized not only in straight state, but also in elastic bent state and plastic bent state.

Self-Interference of Exciton Emission in Organic Single Crystals Visualized by Energy-Momentum Spectroscopy

We employ energy-momentum spectroscopy on isolated organic single crystals with micrometer-sized dimensions. The single crystals are grown from a thiophene-based oligomer and are excellent low-loss active waveguides that support multiple guided modes. Excitation of the crystals with a diffraction-limited laser spot results in emission into guided modes as well as into quasi-discrete radiation modes. These radiation modes are mapped in energy-momentum space and give rise to dispersive interference patterns. On the basis of the known geometry of the crystals, especially the height, the characteristics of the interference maxima allow one to determine the energy dependence of two components of the anisotropic complex refractive index. Moreover, the method is suited to identify the orientation of molecules within (and around) a crystalline structure.

Acid···Amide Supramolecular Synthon in Cocrystals: From Spectroscopic Detection to Property Engineering

The acid···amide dimer heterosynthon in cocrystals of aromatic acids and primary amides is identified by marker peaks in the IR spectra that are characteristic of individual N-H···O and O-H···O interactions and also of the extended synthon. The O-H···O hydrogen bond is crucial to heterodimer formation in contrast to the N-H···O bond. A combinatorial study, tuning the chemical nature of acid and amide functionalities, leads to 22 cocrystals out of 36 crystallization attempts. Four quadrants I-IV are defined based on acidity and basicity of the acid and amide components. The strong acid-strong base combination in quadrant I favors the planar acid···amide heterodimer in its eight cocrystals. Quadrant IV with its weak acid-weak base combination is the least favored for the planar heterosynthon and synthon diversity is observed in the eight cocrystals obtained. The strong-weak and weak-strong combinations in quadrants II and III are expectedly ambivalent. This exercise highlights the effect of molecular features on supramolecular behavior. Quadrant I crystals, with their propensity for the planar acid···amide heterodimer are suitable for the engineering of crystals that can be sheared. This quadrant favors the formation of elastic crystals too. The overall result is that 57% (4 in 7) of all crystals in this quadrant are deformable, compared with 14% (1 in 7) in the three other quadrants. This work is a complete crystal engineering exercise from synthon identification to a particular desired crystal packing to property selection. One can virtually anticipate the mechanical property of a putative acid···amide cocrystal from a knowledge of just the molecular structures of the constituent acid and amide molecules.

Hand-twistable plastically deformable crystals of a rigid small organic molecule

The crystals of the small rigid molecule 4-bromobenzonitrile exhibit highly flexible plastic bending behaviour that occurs on two perpendicular faces of the crystal, a rare situation, leading to the formation of helical/twisted and curled crystals.

Controllable morphology and self-assembly of one-dimensional luminescent crystals based on alkyl-fluoro-substituted dithienophenazines

A class of dithienophenazine derivatives, 9,10-difluoro-2,5-dialkyldithieno[3,2-a:2′,3′-c]phenazine (F-n, n = 4, 5, 6, 7 and 8), modified with various lengths of linear alkyl chains were synthesized and used as building blocks to assemble luminescent one-dimensional (1D) nano/microcrystals.

Fabrication routes for one-dimensional nanostructures via block copolymers

Nanotechnology is the field which deals with fabrication of materials with dimensions in the nanometer range by manipulating atoms and molecules. Various synthesis routes exist for the one, two and three dimensional nanostructures. Recent advancements in nanotechnology have enabled the usage of block copolymers for the synthesis of such nanostructures. Block copolymers are versatile polymers with unique properties and come in many types and shapes. Their properties are highly dependent on the blocks of the copolymers, thus allowing easy tunability of its properties. This review briefly focusses on the use of block copolymers for synthesizing one-dimensional nanostructures especially nanowires, nanorods, nanoribbons and nanofibers. Template based, lithographic, and solution based approaches are common approaches in the synthesis of nanowires, nanorods, nanoribbons, and nanofibers. Synthesis of metal, metal oxides, metal oxalates, polymer, and graphene one dimensional nanostructures using block copolymers have been discussed as well.

In situhigh pressure study of an elastic crystal by FTIR spectroscopy

Anin situhigh pressure-FTIR study on a 2,3-dichlorobenzylidine-4-bromoaniline elastic crystal shows significant structural changes at high pressure which revert back to the ambient structure on decompression.

A hand-twisted helical crystal based solely on hydrogen bonding

Third-generation crystal engineering: using halogen bond/hydrogen bond equivalence.

Cu2O hollow structures—microstructural evolution and photocatalytic properties

Cu₂O single-shelled, multi-shelled and multi-shelled porous sub-micron hollow spheres were successfully synthesized via a facile one-pot route. The Cu₂O multi-shelled hollow sub-micron spheres demonstrated the best photo-catalytic property.

Highly bent crystals formed by restrained π-stacked columns connected via alkylene linkers with variable conformations

A reproducible formation of strongly bent crystals was accomplished by structurally restraining macrocyclic π-conjugated molecules. The model π-units consist of two 9,10-bis(2-thienylethynyl)anthracenes with a strong propensity for stacking, which are connected in a macrocyclic fashion via two alkylene linkers. The correlation between the crystalline morphology and the macrocyclic structures restrained by a variety of flexible alkylene linker combinations was systematically studied. Bent crystals were obtained only with specific alkylene linkers of appropriate chain length. The alkylene linkers can adopt different conformations in the crystal packing, so as to fill voids within the macrocycle. The ability to form several similar molecular structures with different alkylene conformations gives rise to contaminations of different crystalline phases within a single crystal, and it is these phase contaminations which are responsible for the bending of the crystals.

Organic nanowire fabrication and device applications

Organic nanowires (ONWs) are flexible, stretchable, and have good electrical properties, and therefore have great potential for use in next-generation textile and wearable electronics. Analysis of trends in ONWs supports their great potential for various stretchable and flexible electronic applications such as flexible displays and flexible photovoltaics. Numerous methods can be used to prepare ONWs, but the practical industrial application of ONWs has not been achieved because of the lack of reliable techniques for controlling and patterning of individual nanowires. Therefore, an "individually controllable" technique to fabricate ONWs is essential for practical device applications. In this paper, three types of fabrication methods of ONWs are reviewed: non-alignment methods, massive-alignment methods, and individual-alignment methods. Recent research on electronic and photonic device applications of ONWs is then reviewed. Finally, suggestions for future research are put forward.

Fabrication and physical properties of self-assembled ultralong polymer/small molecule hybrid microstructures

The present work showed a novel approach to fabricate polymer/small molecule hybrid microstructures, and the transport characteristics and morphologies of the as-fabricated wires with different ratios of the two different components.

Laser Emission from Ring Resonators Formed by a Quantum-Dot-Doped Single Polymer Nanowire

Laser emission from nanowire-based devices is important for nanophotonic applications. Here we report the observation of optically pumped laser emission from ring resonators formed by quantum-dot-doped single polymer nanowire. By assembling a 500 nm diameter single polymer nanowire with an optical loss coefficient of 70 cm^-1 to form a ring resonator with a short diameter of 20 μm and a large diameter of 40 μm, multimode laser emission with mode number of 9 is obtained in the wavelength region from 550 to 650 nm. The dominant emission is 600 nm wavelength with a line width of 0.8 nm, a Q factor of 400, and a low lasing threshold of 100 μJ/cm² under a 550 nm green laser pump.

Photonic nanowires: from subwavelength waveguides to optical sensors

Nanowires are one-dimensional (1D) nanostructures with comparatively large aspect ratios, which can be useful in manipulating electrons, photons, plasmons, phonons, and atoms for numerous technologies. Among various nanostructures for low-dimensional photonics, the 1D nanowire is of great importance owing to its ability to route tightly confined light fields in single-mode with lowest space and material requirements, minimized optical path, and high mechanical flexibilities. In recent years, nanowire photonics have increasingly been attracting scientists' interests for both fundamental studies and technological applications because 1D nanowires have more favorable properties than many other structures, such as 0D quantum dots (QDs) and 2D films. As subwavelength waveguides, free-standing nanowires fabricated by either chemical growth or physical drawing techniques surpass nanowaveguides fabricated by almost all other means in terms of sidewall smoothness and diameter uniformity. This conveys their low waveguiding losses. With high index contrast (typically higher than 0.5) between the core and the surrounding or with surface plasmon resonance, a nanowire can guide light with tight optical confinement. For example, the effective mode area is less than λ(2)/10 for a dielectric nanowire or less than λ(2)/100 for a metal nanowire, where λ is the vacuum wavelength of the light. As we increase the wavelength-to-diameter ratio (WDR) of a nanowire, we can enlarge the fractional power of the evanescent fields in the guiding modes to over 80% while maintaining a small effective mode area, which may enable highly localized near-field interaction between the guided fields and the surrounding media. These favorable properties have opened great opportunities for optical sensing on the single-nanowire scale. However, several questions arise with ongoing research. With a deep-subwavelength cross-section, how can we efficiently couple light into a single nanowire? How can we fabricate a nanowire with low optical loss? How can we activate a passive nanowire for optical sensing? And lastly, how can we adapt mature optical measurement technology onto a nanowire? In this Account, we highlight our initial attempts to address the above-mentioned challenges. First, we introduce the fabrication and functionalization of low-loss photonic nanowires. We show that nanowires fabricated by either top-down physical drawing (e.g., for amorphous nanowires) or bottom-up chemical growth (e.g., for crystalline nanowires) can yield excellent geometric and structural uniformities with surface roughness down to atomic level and minimize the scattering loss for subwavelength optical or plasmonic waveguiding. Then, relying on a near-field fiber-probe micromanipulation, we demonstrate optical launching of single nanowires by evanescent coupling, with coupling efficiency up to 90% for dielectric nanowires and 80% for plasmonic nanowires. Third, we discuss the waveguiding properties of nanowires and emphasize their outstanding capability of waveguiding tightly confined optical fields with high fractional evanescent fields. In addition, we briefly show a balance between the loss, confinement, and bandwidth in a waveguiding nanowire. Fourthly, we present promising approaches to single-nanowire optical sensors. By measuring optical absorption or spectral transmission of a nanowire and activating nanowires with sensitive dopants, we demonstrate a single-nanowire optical sensor with high sensitivity, fast response, and low optical power. This may lead to a novel platform for optical sensing at nanoscale. Finally, we conclude with an outlook for future challenges in the light manipulation and sensing applications of photonic nanowires.

Self-assembly of sodium 4-(4,5-diphenyl-1H-imidazol-2-yl)benzoate into ultralong microbelts

Ultralong SDB microbelts with interesting optical and electrical properties were successfully fabricated by the poor solvent mediated self-assembly method.

In situ integration of squaraine-nanowire-array-based Schottky-type photodetectors with enhanced switching performance

Organic nanostructure-based photodetectors are important building blocks for future high-performance, low-cost, flexible nano-optoelectronic devices. However, device integration remains a large challenge, and the structure-dependent performance of the device has been seldom studied. Here, we report the in situ integration of 2,4-bis[4-(N,N-dimethylamino)phenyl]squaraine (SQ)-nanowire (NW)-array-based photodetectors by growing the organic NW arrays on prefabricated electrodes through an evaporation-induced self-assembly process. In contrast with ohmic-contact devices, asymmetric electrode pairs of Au-Ti were utilized to achieve the construction of Schottky-type photodetectors on the basis of organic NW arrays. Significantly, the Schottky-type photodetectors exhibited a significantly enhanced performance as compared to the ohmic-type devices in terms of their higher photosensitivity and switching speed. The presence of a strong built-in electric field at the junction interface, which greatly facilitated the separation/transportation of photogenerated electron-hole pairs, was suggested to be responsible for the superior performance of the Schottky-type photodetectors. More importantly, the organic NW-array-based devices also showed a higher sensitivity and reproducibility than that of the single NW-based devices, and they were capable of low-light detection. The investigation of the photodetector circuitry also disclosed a very low pixel-to-pixel variation owing to the average effect of the NW-array-based devices. It is expected that organic NW-array-based Schottky-type photodetectors will have important applications in future organic nano-optoelectronic 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.

Optical microring resonators constructed from organic dye nanofibers and their application to miniaturized channel drop/add filters

We fabricated micrometer-scale optical ring resonators by micromanipulation of thiacyanine (TC) dye nanofibers that propagate exciton polaritons (EPs) along the fiber axis. High mechanical flexibility of the nanofibers and a low bending loss property of EP propagation enabled the fabrication of microring resonators with an average radius (r(ave)) as small as 1.6 μm. The performances of the fabricated resonators (r(ave) = 1.6-8.9 μm) were investigated by spatially resolved microscopy techniques. The Q-factors and finesses were evaluated as Q ≈ 300-3500 and F ≈ 2-12. On the basis of the r(ave)-dependence of resonator performances, we revealed the origin of losses in the resonators. To demonstrate the applicability of the microring resonators to photonic devices, we fabricated a channel drop filter that comprises a ring resonator (r(ave) = 3.9 μm) and an I/O bus channel nanofiber. The device exhibited high extinction ratios (4-6 dB) for its micrometer-scale dimensions. Moreover, we successfully fabricated a channel add filter comprising a ring resonator (r(ave) = 4.3 μm) and two I/O bus channel nanofibers. Our results demonstrated a remarkable potential for the application of TC nanofibers to miniaturized photonic circuit devices.