Byeong-Kwan An

Tailor-Made Highly Luminescent and Ambipolar Transporting Organic Mixed Stacked Charge-Transfer Crystals: An Isometric Donor–Acceptor Approach

We have rationally designed a densely packed 1:1 donor-acceptor (D-A) cocrystal system comprising two isometric distyrylbenzene- and dicyanodistyrylbenzene-based molecules, forming regular one-dimensional mixed stacks. The crystal exhibits strongly red-shifted, bright photoluminescence originating from an intermolecular charge-transfer state. The peculiar electronic situation gives rise to high and ambipolar p-/n-type field-effect mobility up to 6.7 × 10(-3) and 6.7 × 10(-2) cm(2) V(-1) s(-1), respectively, as observed in single-crystalline OFETs prepared via solvent vapor annealing process. The unique combination of favorable electric and optical properties arising from an appropriate design concept of isometric D-A cocrystal has been demonstrated as a promising candidate for next generation (opto-)electronic materials.

Stimuli-Responsive Reversible Fluorescence Switching in a Crystalline Donor-Acceptor Mixture Film: Mixed Stack Charge-Transfer Emission versus Segregated Stack Monomer Emission.

We report on a molecularly tailored 1:1 donor-acceptor (D-A) charge-transfer (CT) cocrystal that manifests strongly red-shifted CT luminescence characteristics, as well as noteworthy reconfigurable self-assembling behaviors. A loosely packed molecular organization is obtained as a consequence of the noncentrosymmetric chemical structure of molecule A1, which gives rise to considerable free volume and weak intermolecular interactions. The stacking features of the CT complex result in an external stimuli-responsive molecular stacking reorganization between the mixed and demixed phases of the D-A pair. Accordingly, high-contrast fluorescence switching (red↔blue) is realized on the basis of the strong alternation of the electronic properties between the mixed and demixed phases. A combination of structural, spectroscopic, and computational studies reveal the underlying mechanism of this stimuli-responsive behavior.

All-organic coaxial nanocables with interfacial charge-transfer layers: electrical conductivity and light-emitting-transistor behavior

All-organic coaxial nanocables with high electrical conductivity and luminescence properties were fabricated by controlled solution blending of poly(3-hexylthiophene) (P3HT) and 1-cyano-trans-1,2-bis-(3′,5′-bis-trifluoromethyl-biphenyl)ethylene (CN-TFMBE). The coaxial nanocables with interfacial charge-transfer doping layers showed a very high electrical conductivity, a chemical-gating feature of the threshold voltage, and efficient light emission.

Single-crystalline organic nanowires with large mobility and strong fluorescence emission: a conductive-AFM and space-charge-limited-current study†

We have designed and synthesized self-assembled one-dimensional nanowires (1D NWs) from the fused thiophene derivative 2,3-bis(5-(3,5-bis(trifluoromethyl)phenyl)thiophen-2-yl)acrylonitrile (SS-TFMBE). This new material is characterized by a strong self-assembling capability that leads to the formation of 1D NWs exhibiting a dramatic increase in fluorescence emission upon formation of NW aggregates. In addition, the semiconducting properties of the 1D NWs were evidenced by means of conducting-probe atomic force microscopy (CP-AFM) and space-charge-limited-current (SCLC) measurements, which show that SS-TFMBE NWs composed of ordered percolated crystals have an effective carrier mobility of up to 3.1 cm2V−1 s−1.

Fabrication of a Patterned Assembly of Semiconducting Organic Nanowires

The current interest in organic semiconductors arises from their synthetic facility, their solution processability, and their potential applications for the fabrication of electrical devices. Among semiconductors of this type, those based on organic nanowires are particularly interesting because of their outstanding self-assembly characteristics and anisotropic optical properties. Several research groups have reported various kinds of functional organic nanowires. While some of these wires exhibit electrical conductivity and mobility, others emit polarized photoluminescence (PL). In spite of these special characteristics, nanowires often form entangled coil-like structures. Therefore, much effort has been made to align the wires in a better way. Various methods, such as electric-field assembly, Langmuir–Blodgett process, and soft lithography have been applied for this purpose. However, it is still difficult to manipulate these randomly generated nanowires one-dimensionally and direct them to the desired position, for example, toward electrode channels for fabricating electrical or optical devices with polarized emission. Among these methods, soft lithography is considered one of the most promising patterning tools because of its simplicity and high efficiency. While inorganic nanowires are frequently patterned by means of soft lithography, only a few organic semiconducting nanowires have been aligned using this process due to their unsatisfactory fluidic selfassembling and structure-forming characteristics. Thus, the kernel of organic nanowire patterning via soft lithography is the development of nanowires with high self-assembly capability. It should be meaningful to align these developed semiconducting nanowires for measuring their electrical and optical properties by the MIMIC (micromolding in capillaries) method, which is one of the effective soft lithography processes. In the present study, we used 1-cyano-trans-1,2-bis-(30,50bis-trifluoromethyl-biphenyl)ethylene (CN-TFMBE) for nanowire patterning. CN-TFMBE was chosen because some of

Self-assembled perpendicular growth of organic nanoneedles via simple vapor-phase deposition: one-step fabrication of a superhydrophobic surface

We demonstrate a simple vapor-phase fabrication of self-assembled perpendicular organic nanoneedles on various substrates to generate superhydrophobic surfaces on them.

High performance n-type organic transistors based on a distyrylthiophene derivative

Organic field-effect transistors (OFETs) based on a distyryl-thiophene (DST) derivative, 3′-(thiophene-2,5-diyl)bis(2-(3,5-bis(trifluoromethyl)phenyl)acrylonitrile (THIO-Y), were fabricated. Attributed to strong intermolecular interactions, dense molecular packing and appropriate energy level, OFETs based on a single crystal and thin film of THIO-Y showed electron mobilities as high as 0.16 and 0.03 cm2 V−1s−1, respectively.

Recent progress in the use of fluorescent and phosphorescent organic compounds for organic light-emitting diode lighting

Abstract. Organic light-emitting diodes (OLEDs) have attracted considerable attention in both academic and industrial circles. Certain properties of OLEDs make them especially attractive in the lighting market, including area emission characteristics not found in other existing light sources, environmentally friendly efficient use of energy, large area, ultra-light weight, and ultra-thin shape. Fluorescent and phosphorescent materials that are being applied to white OLEDs have been categorized, and the chemical structures and device performances of the important blue, orange, and red light-emitting materials have been summarized. Such a systematic classification and understanding of the materials that have already been reported can aid the development and study of new light-emitting materials through quantitative and qualitative approaches.

Selected-area in situ generation of highly fluorescent organic nanowires embedded in a polymer film: the solvent-vapor-induced self-assembly process

The preparation of highly fluorescent one-dimensional (1D) nanostructures within a selected area of a solid substrate is a challenging requirement for the realization of optoelectronic nanodevices. We present a novel method for fabricating highly fluorescent organic nanowires (NWs) embedded in a variety of polymer films through the combined processes of photochemical lithography and solvent–vapor annealing (SVA). To achieve this, we designed and synthesized an acid-responsive organic fluorophore bearing a self-assembly moiety. The in situ self-assembly of this fluorophore into ultralong nanowires proceeds selectively in designated regions of the polymer matrix via a simple selected-area SVA process. The I–V electrical characteristics of 2-(3′,5′-bis(trifluoromethyl)biphenyl-4-yl)-3-(6-3,5-bis(trifluoromethyl)phenyl)pyridine-3-yl)acrylonitrile (Py-CN-TFMBE) structures, self-assembled using the SVA method, were measured on a two-terminal electrode device. This unique fabrication approach, which combines photochemical lithography and SVA, eliminates the difficulties of transferring preformed 1D organic nanostructures to fixed locations on a substrate, thereby establishing a new method for the fabrication control of optoelectronic nanodevices.

Novel Blue Organic Light Emitting Materials

The new blue light emitting materials containing anthracene were designed, synthesized and characterized. The materials were prepared in high yields by well-known reactions such as Grignard reaction, synthesis of boronic acid, and Suzuki coupling reaction. The non-coplanar structures of materials were confirmed by using the PM3 parameterization in the Hyper Chem 5.0 program (Hypercube) in order to fully optimize the structure of molecule. The obtained materials showed a thermal stability and a good film forming ability. It is found that the energy transfer from substituents to anthracene took place effectively.