Sanghyuk Park

A White-Light-Emitting Molecule: Frustrated Energy Transfer between Constituent Emitting Centers

White-light-emitting single molecules are promising materials for use in a new generation of displays and light sources because they offer the possibility of simple fabrication with perfect color reproducibility and stability. To realize white-light emission at the molecular scale, thereby eliminating the detrimental concentration- or environment-dependent energy transfer problem in conventional fluorescent or phosphorescent systems, energy transfer between a larger band-gap donor and a smaller band-gap acceptor must be fundamentally blocked. Here, we present the first example of a concentration-independent ultimate white-light-emitting molecule based on excited-state intramolecular proton transfer materials. Our molecule is composed of covalently linked blue- and orange-light-emitting moieties between which energy transfer is entirely frustrated, leading to the production of reproducible, stable white photo- and electroluminescence.

Highly efficient and stable deep-blue emitting anthracene-derived molecular glass for versatile types of non-doped OLED applications

New anthracene-based deep-blue emitting molecular glass, 9-(9-phenylcarbazole-3-yl)-10-(naphthalene-1-yl)anthracene (PCAN), which is asymmetrically functionalized with N-phenylcarbazole and naphthalene, has been designed, synthesized, and characterized. The deep-blue emitting PCAN is efficiently secured for color purity, has high glass transition temperature (Tg = 151 °C), and has excellent solubility (>100 mg mL−1 in toluene), due to its highly tilted asymmetric molecular conformation. Using processing versatility of PCAN, vacuum-deposited and solution-processed non-doped deep-blue fluorescent organic light-emitting diodes (OLEDs) were prepared, which employ PCAN as an emitter. The vacuum deposited, non-doped EL device exhibited not only the excellent luminance efficiency and external quantum efficiency (as high as 3.64 cd A−1 and 4.61%, respectively) for the saturated deep-blue CIE chromaticity coordinates of (0.151, 0.086), but also stable performance and a good device lifetime. Furthermore, the solution processed EL device also exhibited an encouraging level of performance (1.24%, 1.15 cd A−1) and deep-blue emission (0.159, 0.105).

Highly efficient deep-blue emitting organic light emitting diode based on the multifunctional fluorescent molecule comprising covalently bonded carbazole and anthracene moieties

High performance deep-blue organic light-emitting diodes (OLEDs) have been investigated using new multifunctional blue emitting materials 3-(anthracen-9-yl)-9-ethyl-9H-carbazole (AC), 3,6-di(anthracen-9-yl)-9-ethyl-9H-carbazole (DAC), 3-(anthracen-9-yl-)-9-phenyl-9H-carbazole (P-AC), and 3,6-di(anthracen-9-yl)-9-phenyl-9H-carbazole (P-DAC) which comprise covalently bonded carbazole and anthracene moieties. We also have investigated the thermal, electrochemical, and morphological stability to find suitable molecular structure, consisting of carbazole and anthracene moieties. The non-doping deep-blue OLEDs using P-DAC, which showed the highest thermal, electrochemical, and morphological stability, proved the highest luminance efficiency and external quantum efficiency of 3.14 cd A−1 and 2.75%, with the Commission Internationale de lEclairage (CIE) chromaticity coordinates (0.162, 0.136) at 100 mA cm−2. Moreover, the doping devices using P-DAC as the host material showed blue emission, and the high luminance efficiencies and external quantum efficiencies of as high as 7.70 cd A−1 and 4.86% with CIE chromaticity coordinates (0.156, 0.136) and (0.156, 0.217) at 100 mA cm−2. Both the non-doping and doping devices using P-DAC uniquely exhibited high operational stability with virtually negligible efficiency roll-off over the broad current density range.

Realizing Molecular Pixel System for Full-Color Fluorescence Reproduction: RGB-Emitting Molecular Mixture Free from Energy Transfer Crosstalk

A full-color molecular pixel system is realized for the first time using simple mixtures composed of RGB-emitting excited-state intramolecular proton transfer (ESIPT) dyes, each of which has delicately tailored Stokes shift and independent emission capability completely free from energy transfer crosstalk between them. It is demonstrated that the whole range of emission colors enclosed within the RGB color triangle on the CIE 1931 diagram is predictable and conveniently reproducible from the RGB molecular pixels not only in the solution but also in the polymer film. It must be noted that mixing ratios to reproduce the desired color coordinates can be precisely calculated on the basis of additive color theory according to their molecular pixel behavior.

Gelation‐Induced Enhanced Fluorescence Emission from Organogels of Salicylanilide‐Containing Compounds Exhibiting Excited‐State Intramolecular Proton Transfer: Synthesis and Self‐Assembly

Self-assembly structure, stability, hydrogen-bonding interaction, and optical properties of a new class of low molecular weight organogelators (LMOGs) formed by salicylanilides 3 and 4 have been investigated by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), UV/Vis absorption and photoluminescence, as well as theoretical studies by DFT and semiempirical calculations with CI (AM1/PECI=8) methods. It was found that salicylanilides form gels in nonpolar solvents due to pi-stacking interaction complemented by the presence of both inter- and intramolecular hydrogen bonding. The supramolecular arrangement in these organogels predicted by XRD shows lamellar and hexagonal columnar structures for gelators 3 and 4, respectively. Of particular interest is the observation of significant fluorescence enhancement accompanying gelation, which was ascribed to the formation of J-aggregates and inhibition of intramolecular rotation in the gel state.

High-Performance Stretchable Conductive Composite Fibers from Surface-Modified Silver Nanowires and Thermoplastic Polyurethane by Wet Spinning

Highly stretchable and conductive fibers have attracted great interest as a fundamental building block for the next generation of textile-based electronics. Because of its high conductivity and high aspect ratio, the Ag nanowire (AgNW) has been considered one of the most promising conducting materials for the percolation network-based conductive films and composites. However, the poor dispersibility of AgNWs in hydrophobic polymers has hindered their application to stretchable conductive composite fibers. In this paper, we present a highly stretchable and conductive composite fiber from the co-spinning of surface-modified AgNWs and thermoplastic polyurethane (PU). The surface modification of AgNWs with a polyethylene glycol derivative improved the compatibility of PU and AgNWs, which allowed the NWs to disperse homogeneously in the elastomeric matrix, forming effective percolation networks and causing the composite fiber to show enhanced electrical and mechanical performance. The maximum AgNW mass fraction in the composite fiber was 75.9 wt %, and its initial electrical conductivity was as high as 14u2009205 S/cm. The composite fibers also exhibited superior stretchability: the maximum rupture strain of the composite fiber with 14.6 wt % AgNW was 786%, and the composite fiber was also conductive even when it was stretched up to 200%. In addition, 2-dimensional (2-D) Ag nanoplates were added to the AgNW/PU composite fibers to increase the stability of the conductive network under repeated stretching and releasing. The Ag nanoplates acted as a bridge to effectively prevent the AgNWs from slippage and greatly improved the stability of the conductive network.

Safety Monitoring Sensor for Underground Subsidence Risk Assessment Surrounding Water Pipeline

IoT(Internet of Things) based underground risk assessment system surrounding water pipeline enables an advanced monitoring and prediction for unexpected underground hazards such as abrupt road-side subsidence and urban sinkholes due to a leak in water pipeline. For the development of successful assessment technology, the PSU(Water Pipeline Safety Unit) which detects the leakage and movement of water pipes. Then, the IoT-based underground risk assessment system surrounding water pipeline will be proposed. The system consists of early detection tools for underground events and correspondence services, by analyzing leakage and movement data collected from PSU. These methods must be continuous and reliable, and cover certain block area ranging a few kilometers, for properly applying to regional water supply changes.

25.1: Invited Paper: White‐emitting Molecule: ‘Molecular Pixel’ from Covalently Bonded Sub‐pixels

In this presentation, we demonstrate the synthesis and properties of two-color emitting ‘molecular pixel’. Our molecule is composed of covalently linked blue- and orange-light-emitting moieties between which energy transfer is entirely frustrated, leading to the production of reproducible and stable white photo-/electroluminescence.

Amplified Spontaneous Emission in Organic Solids Composed of Excited-State Intramolecular Proton Transfer Molecules

Amplified spontaneous emission associated with excited-state intramolecular proton transfer was investigated in organic single crystals and glasses. The closely packed single crystals were shown to be a promising candidate for gain medium for pulsed excitation.