http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Ham, Sujin,Lee, Ji-Eun,Song, Suhwan,Peng, Xiaobin,Hori, Takaaki,Aratani, Naoki,Osuka, Atsuhiro,Sim, Eunji,Kim, Dongho The Royal Society of Chemistry 2016 Physical chemistry chemical physics Vol.18 No.5
<P>By utilizing single-molecule defocused wide-field fluorescence microscopy, we have investigated the molecular structural properties such as transition dipole moment orientations and the angular relationship among chromophores, as well as structural distortions and flexibilities depending on the ring size, in a series of cyclic porphyrin arrays bearing close likeness in overall architectures to the LH2 complexes in purple bacterial photosynthetic systems. Furthermore, comparing the experimental results with molecular dynamics simulations, we ascertained site selection for fluorescent trapping sites. Collectively, these experimental and computational results provide the basis for structure-property relationships and energy hopping/emitting processes in an important class of artificial light-harvesting molecular systems widely used in molecular electronics technology.</P>
Ham, Sujin,Chung, Heejae,Kim, Tae-Woo,Kim, Jiwon,Kim, Dongho The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.5
<P>Lead halide perovskite nanoparticles (NPs) are attractive as they exhibit excellent color purity and have a tunable band gap, and can thus be applied in highly efficient photovoltaic and light-emitting diodes. Fundamental studies of emission linewidth broadening due to spectral shifts in perovskite NPs may suggest a way to improve their color purity. However, the carrier-induced Stark shift that causes spectral diffusion still requires investigation. In this study, we explore composition-related emission linewidth broadening by comparing CsPbBr3 and CH3NH3PbBr3 (MAPbBr3) perovskite NPs. We find that the MAPbBr3 NPs are more sensitive to fluctuations in the local electric fields than the CsPbBr3 NPs due to an intrinsic difference in the dipole moment between the two A cations (Cs and MA), which shows a carrier-induced Stark shift. The results indicate that the compositions of perovskite NPs are closely associated with emission linewidth broadening and they also provide insights into the development of NP-based devices with high color purity.</P>
Ham, Sujin,Choi, Yung Ji,Lee, Jin-Wook,Park, Nam-Gyu,Kim, Dongho American Chemical Society 2017 The Journal of Physical Chemistry Part C Vol.121 No.5
<P>Since the discovery of organometallic trihalide perovskites, there have been tremendous efforts to exploit these hybrid materials and understand their optoelectronic properties for the development of solar cells with high power conversion efficiencies. Although the improved performance of perovskite solar cells with excess CH3NH3I has been reported, the dedicated research of the free charge carrier dynamics is lacking. In this study, we measured the photoluminescence (PL) intensities and lifetimes at the grains and near the grain boundaries of CH3NH3PbI3 perovskite films using spatially and temporally resolved PL spectroscopy. An excess CH3NH3I was found to cause brighter PL intensities and longer PL lifetimes at both the grains and grain boundaries. This comparative investigation of stoichiometric and nonstoichiometric perovskite films enables us to understand the optoelectronic properties induced by excess CH3NH3I, opening a new way for optimization of perovskite solar cells.</P>
Ham, Sujin,Lee, Sang Hyeon,Chung, Heejae,Kim, Dongho The Royal Society of Chemistry 2016 Physical chemistry chemical physics Vol.18 No.10
<P>The photophysical properties of a series of highly pi-conjugated benzoporphyrin molecules (BPNs) with different shapes were investigated in the condensed phase using single-molecule fluorescence spectroscopy. The fluorescence properties of single BPNs were found to be affected by the number of porphyrin units and their molecular shapes. Notably, the single-molecule fluorescence dynamics of the BPNs revealed an increase in the fluorescence lifetimes and blue shifts of the fluorescence spectra indicative of decreasing pi-conjugation pathways in the molecules. The distributions of the spectroscopic parameters and the photostability for the molecules also suggest conformational complexities and heterogeneities. Specifically, as the number of constituent porphyrin units increased, the one-step photobleaching behavior ratio and photostability decreased, and the spectroscopic parameter distributions broadened. The structural properties of the BPNs were also directly determined using defocused wide-field imaging and linear dichroism analyses. In particular, molecules with the same number of constituent porphyrins but different molecular shapes exhibited distinct photophysical properties. In summary, these observations provide guidance for the design of molecular systems that can enhance the performance of molecular electronic devices.</P>
Kim, Taehee,Ham, Sujin,Lee, Sang Hyeon,Hong, Yongseok,Kim, Dongho The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.35
<P>Exciton transport in <I>meso</I>-tetra(4-sulfonatophenyl) porphyrin (TPPS) J-aggregates was directly imaged using the emission profile analysis method with confocal fluorescence microscopy. By controlling the structural hierarchy of TPPS aggregates, we could comparatively study the exciton transport properties in single nanotubes and bundled structures. Using the one-dimensional diffusion model, the exciton diffusion coefficients of TPPS nanotubes and bundles were estimated as 95 and 393 nm<SUP>2</SUP> ps<SUP>−1</SUP>, respectively, showing a dramatic enhancement of exciton transport in bundled structures. To reveal the underlying mechanism of enhanced exciton transport in bundle compared to that in single strands, the spatially resolved measurements of exciton transport images were correlated with the spectral information at each local sites. We have confirmed that nanotube and its bundled form possess different energetic landscapes and exciton migration dynamics. Agglomeration into bundles led to an increase in system-environment coupling and denser distribution of energy states, facilitating longer migration length and accelerated transport. Detailed analysis in this study provides important insights into the structure-dependent exciton transport properties of self-assembled J-aggregate nanostructures.</P>