https://scholar.korea.ac.kr/handle/2021.sw.korea/806 2026-04-05T15:57:21Z 2026-04-05T15:57:21Z Jeong, Seong Woon Lee, Hyung Joo Park, Bum June Bong, Min-Jong Lee, Daehan Kim, Taekyung Kim, Chul Hoon Son, Ho-Jin https://scholar.korea.ac.kr/handle/2021.sw.korea/270670 2025-05-28T09:01:30Z 2025-05-09T00:00:00Z

Title: Organic phosphorescence in Pt(II)-complexes linked to organic chromophores for blue-emitting organic light-emitting diodes Authors: Jeong, Seong Woon; Lee, Hyung Joo; Park, Bum June; Bong, Min-Jong; Lee, Daehan; Kim, Taekyung; Kim, Chul Hoon; Son, Ho-Jin Abstract: Recently, organic persistent room-temperature phosphorescence (OPRTP), entailing triplet-state emission from purely organic units instead of luminescent heavy metal complexes, has emerged as a promising alternative for the development of emitting materials in organic light-emitting diodes (OLEDs). For OPRTP-based devices to achieve acceptable performances, the low emission efficiency caused by weak spin-orbit coupling and high sensitivity to external environmental factors, such as temperature, moisture, and oxygen must be overcome. Herein, four-coordinate N-heterocyclic carbene Pt(II) complexes bearing carbazole (Cz) or naphthalene (Np) groups were assembled and found to exhibit exothermic triplet-triplet energy transfer (TTET) from the high triplet metal-to-ligand charge transfer (3MLCT) state (T1 = 2.97 eV) of the Pt core to the lower triplet states (T1 = 2.58-2.87 eV) of the tethered organic Cz and Np moieties. The presented design strategy enables the persistent organic phosphorescence of organic molecules under ambient conditions and triplet electroluminescence of the organic group via TTET in OLED applications.

2025-05-09T00:00:00Z Ha, Insung Cho, Hyun Woo Lee, Hyung Joo Ravindran, Ezhakudiyan Jesuraj, P. Justin Lee, Jae Woo Lee, Chang Min Kim, Chul Hoon Ryu, Seung Yoon https://scholar.korea.ac.kr/handle/2021.sw.korea/267519 2025-05-22T01:00:16Z 2025-02-08T00:00:00Z

Title: Exploring the Origin of White Emission in TAPC: Electron Transport Layer Based Exciplex Devices Authors: Ha, Insung; Cho, Hyun Woo; Lee, Hyung Joo; Ravindran, Ezhakudiyan; Jesuraj, P. Justin; Lee, Jae Woo; Lee, Chang Min; Kim, Chul Hoon; Ryu, Seung Yoon Abstract: This study investigated white organic light-emitting diodes (OLEDs) with a single emissive layer and comprising a hole transport material 1,1-Bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and two electron transport materials 1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) and 1,3,5-tris(3-pyridyl-3-phenyl)benzene (TmPyPB). The devices exhibited unique emission characteristics, from sky blue and orange exciplex emissions at low voltages to yellow electromer emissions at higher voltages. The combination of these emissions results in a distinctive white light output. To understand the origin of the white emission, time-resolved photoluminescence and time-resolved area-normalized emission spectra analyses are employed. These techniques provided insights into the exciton dynamics in the OLED devices and facilitated the determination of mechanisms underlying the white light emission. The investigation highlights the significant effect of intermolecular bonding between materials, which enhances the understanding of the molecular dynamics associated with white emission. Notably, the findings indicate that TPBi facilitates the generation of tightly bound exciplexes owing to its rigid and planar structure, while TmPyPB promotes the formation of loosely bound exciplexes owing to its flexible and nonplanar structure. The observed temporal evolution of emission characteristics improves the understanding of white emission OLEDs with a simple structure and offers insights into the design and optimization of OLEDs.

2025-02-08T00:00:00Z Ko, Semin Lee, Hyun Jae Jeong, Hyeon Woo Kim, Ja Yeon Lee, Seon Joo Lee, Jaemin Yun, Sun Jin Kim, Chul Hoon Choi, Sungho https://scholar.korea.ac.kr/handle/2021.sw.korea/267318 2025-04-02T03:00:51Z 2025-02-06T00:00:00Z

Title: Selective Dispersing Solvent-Assisted Surface Defect Engineering Followed by Time-Resolved Spectroscopy Analysis of Red-Emitting CsPb(Br,I)<sub>3</sub> Nanocrystals for Stable and Bright Light-Emitting Diodes Authors: Ko, Semin; Lee, Hyun Jae; Jeong, Hyeon Woo; Kim, Ja Yeon; Lee, Seon Joo; Lee, Jaemin; Yun, Sun Jin; Kim, Chul Hoon; Choi, Sungho Abstract: In the solution process using perovskite nanocrystals (PNCs) as emitting materials for light-emitting diodes (LEDs), solvent orthogonality typically plays a crucial role in preserving stable interfacial conditions between the carrier transport layers on both sides. Unfortunately, there is a lack of clear understanding of which solvent to choose and what effects the solvent has in realizing the photo/electroluminescence (PL and EL) properties of the given PNCs. Here, we investigate the impact of merely changing dispersing solvents on the properties of PNCs, which belong to a family of nonpolar aliphatic hydrocarbons, hexane, octane, and decane. We can realize that by simply postdispersing using longer chain alkane solvents, both the PL/EL properties were improved along with the synthetic yield and uniform PNC particle size distribution, and the suppressed surface defect was found using time-resolved photoluminescence analysis. Samples that underwent dispersion and washing using a decane solvent, which effectively heals the remnant surface defects, were confirmed to have doubled the yield and improved luminous efficiency with superior EL (maximum external quantum efficiency of 14.7%) with reproducible device performances. The given dispersing solvent selection strategy has the potential to enhance the PL and EL properties and thus the reproducibility of perovskite-based LEDs.

2025-02-06T00:00:00Z Lee, Sunhee Lee, Yeeun Hong, Jiwoo Lee, Soyoon Wee, Kyung-Ryang Han, Won-Sik https://scholar.korea.ac.kr/handle/2021.sw.korea/267757 2025-04-01T09:02:10Z 2025-02-05T00:00:00Z

Title: Peripheral substituent effect on 'turn-on' fluorescence of BODIPY derivatives for sensing benzene moieties Authors: Lee, Sunhee; Lee, Yeeun; Hong, Jiwoo; Lee, Soyoon; Wee, Kyung-Ryang; Han, Won-Sik Abstract: In this work, a series of dipyrrometheneboron difluoride (BODIPY) derivatives, BT-F, BT-H, and BT-OMe, was prepared to study the peripheral substituent effect on 'turn-on' fluorescent for benzene moieties including benzene, toluene, and xylene (BTX). The photophysical- and electrochemical properties of the three compounds were systematically studied by steady-state UV-visible and PL spectroscopies, and cyclic voltammetry along with DFT calculations. Among various organic solvents, all compounds selectively showed strong 'turn-on' fluorescence in BTX solvents, proving that these compounds can be used as BTX probes. As the portion of BTX increases, the emission band shows a hypsochromic shift, indicating that the enhanced emission originated from exciplex formation in the excited state. Among them, BT-OMe, which has methoxy groups at peripheral positions, showed the highest sensing capability to BTX. The electron-donating nature of the methoxy group enhances the electron population on the BODIPY core and the triphenylamine groups, which results in strong interaction with BTX in the excited state.

2025-02-05T00:00:00Z