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Junghwa Lee,주태하 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.3
Photophysics of 10-hydroxybenzo[h]quinoline (HBQ) has been in controversy, in particular, on the nature of the electronic states before and after the excited state intramolecular proton transfer (ESIPT), even though the dynamics and mechanism of the ESIPT have been well established. We report highly time resolved fluorescence spectra over the full emission frequency regions of the enol and keto isomers and the anisotropy in time domain to determine the accurate rates of the population decay, spectral relaxation and anisotropy decay of the keto isomer. We have shown that the ~300 fs component observed frequently in ESIPT dynamics arises from the S2→S1 internal conversion in the reaction product keto isomer and that the ESIPT occurs from the enol isomer in S1 state to the keto isomer in S2 state.
류재현,김현우,김명수,주태하 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.2
Proton transfer reaction is one of the most fundamental processes in chemistry and life science. Excited state intramolecular proton transfer (ESIPT) has been studied as a model system of the proton transfer, since it can be conveniently initiated by light. We report ESIPT reaction dynamic of 1-hydroxy-anthraquione (1-HAQ) in solution by highly time-resolved fluorescence. ESIPT time of 1-HAQ is determined to be 45 ± 10 fs directly from decay of the reactant fluorescence and rise of the product fluorescence. High time resolution allows observation of the coherent vibrational wave packet motion in the excited state of the reaction product tautomer. The coherently excited vibrational mode involves large displacement of the atoms, which shortens the distance between the proton donor and the acceptor. With the theoretical analysis, we propose that the ESIPT of 1-HAQ proceeds barrierlessly with assistance of the skeletal vibration, which in turn becomes excited coherently by the ESIPT reaction.
Excited State Intramolecular Proton Transfer Dynamics of Oxadiazole-based Dyes
김진용,김세훈,박수영,주태하 대한화학회 2015 Bulletin of the Korean Chemical Society Vol.36 No.3
Excited state intramolecular proton transfer (ESIPT) dynamics of two oxadiazole-based model compounds, 2,5-bis-[5-(4-tert-butyl-phenyl)-[1,3,4]oxadiazol-2-yl]-phenol (SOX) and 2,5-bis-[5-(4-tert-butyl-phenyl)-[1,3,4]oxadiazol-2-yl]-benzene-1,4-diol (DOX) have been investigated by time-resolved fluorescence. SOX and DOX have one and two intramolecular hydrogen bond moieties, respectively, where ESIPT may occur. Time-resolved fluorescence fully resolves the ESIPT dynamics and establishes the two-state conversion between the enol and keto isomers in the S1 potential energy surface. The apparent inconsistency between the ESIPT rate and the steady-state spectrum is settled by invoking the conformational inhomogeneity including the intermolecular hydrogen bonding with protic solvents. The ESIPT rates of SOX and DOX are not as fast as those of typical ESIPT molecules, which indicates a finite barrier for the reaction. For DOX, ESIPT is enabled for only one hydroxyl moiety, and the ESIIPT rate is twice as fast as that of SOX. We propose a symmetric potential energy surface along the two proton transfer coordinates, and bifurcation of the initial probability density of the enol isomer into the two potential minima representing the keto isomer.
자가 형성된 보머-웨버(Volmer-Weber)형 산화아연 나노 결정체의 시분해 광발광 특성 연구
박세정,황윤회,김형국,박소현,주태하,이익재,김진우,이재호,김양도 한국물리학회 2009 새물리 Vol.58 No.4
Self-assembled Volmer-Weber-type ZnO nanocrystals were fabricated on Pt(111)/TiO2/SiO2/Si(100) substrates by using a RF sputtering method. The structure was analyzed by using a synchrotron X-ray method (at beamline 5C2, Pohang Acceleration Laboratory). The temperature-dependent photoluminescence of the Volmer-Weber ZnO nanocrystals was measured from 6 K to 300 K, and the time-resolved photoluminescence was measured at 12 K. We found from the X-ray experiment that the Volmer-Weber-type ZnO nanocrystals had a c-axis orientation. In the temperature-dependent photoluminescence experiment, two intensive UV emissions, 3.368 eV and 3.312 eV, were observed between 6 K and 20 K. As the temperature was increased, the two peaks combined into one at 3.299 eV. In the time-resolved photoluminescence experiment at 12 K, the dynamics of the peaks at 3.368 eV had one relaxation time of approximately 180 ps and that of the peak at 3.312 eV had three relaxation times of 79 ps, 870 ps and 2.2 ns. 라디오 주파수 마그네트론 스퍼터링 방법을 이용하여 제작한 자가 형성된 보머-웨버 (Volmer-Weber)형 산화아연 나노 결정체의 광학적 특성을 연구하였다. 먼저, 방사광 엑스선 회절 실험 (포항가속기 연구소 5C2 빔라인)을 이용하여 산화아연 나노 결정체의 구조를 분석하였고, 헬륨-카드뮴 레이저 (325 nm)를 이용하여 6 K~ 300 K 범위에서 온도 의존성 광발광 (temperature dependent photoluminescence) 특성과 펨토초 레이저를 이용한 저온 시분해 발광 (low-temperature time-resolved photoluminescence) 특성을 연구하였다. 엑스선 회절 실험에서는 보머-웨버형 산화아연 나노 결정체들이 c축 우선 방향성을 보였다. 온도 의존 광발광 실험에서는 보머-웨버형 산화아연 나노 결정체가 낮은 온도 영역 (6 K~20 K)에서 3.368 eV와 3.312 eV의 두 개의 강한 자외선 발광 특성을 보이나 온도가 증가하면서 두 봉우리가 상온에서 3.299 eV의 에너지를 가지는 하나의 봉우리로 합쳐졌다. 12 K에서 수행된 시분해 광발광 실험에서 측정한 감쇄 함수는 3.368 eV 발광 봉우리의 경우 하나의 완화시간으로 분석할 수 있었으나, 3.312 eV 발광 봉우리는 세 개의 완화시간으로 분석이 가능하였다.
서기호,엄인태,심상덕,김철훈,주태하 대한화학회 2019 Bulletin of the Korean Chemical Society Vol.40 No.4
Photochromic ring closure reaction dynamics of 1,2-bis(2-methylbenzo[b]thiophene-3-yl)hexafluoro cyclopentene is investigated by means of time-resolved fluorescence spectra. Compared with a single wavelength probe, direct measurement of the emission spectra during the reaction provides unambiguous and straightforward picture for the ring closure reaction pathway. We observe two different emission bands in the fluorescence of the open ring isomer. From the global analysis for the spectra, we obtain <1 ps time constant for the ring closure reaction in polar solvent. Moreover, the ring closure reaction of the compound takes place entirely on the ultrafast timescale. The unreactive parallel conformer decays to the ground state by 150?ps time constant.
A Study of Electro-Optical Crystal as a Diagnostic Tool for Low Energy Electron Beam
박용운,김창범,고인수,Jangho Park,황정연,주태하 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.I
The short, intense, and low emittance electron beams are crucial to make high quality X-ray beam for X-ray free electron laser (XFEL). A RF photo-cathode (RF PC) gun of 1.6 cell cavity is installed at Gun Test Stand (GTS) in Pohang Accelerator Laboratory (PAL). For the successful construction of PAL-XFEL, the bunch length of the beam should be measured accurately at the exit of the gun where the beam energy is 4.5 MeV. Electro-Optic Sampling (EOS) is a very promising method to measure the bunch length non-destructively. An experiment with D.C. voltage setup is done to verify the electro-optic (EO) crystal can be used as a diagnostic tool for low energy beam. A simulation study is also done with a pulse propagation method which is based on the Fourier transform that allows us to investigate the dynamical evolution of electromagnetic pulse in the EO crystal. The simulation result shows that the signal level can be about 20 \% of the initial laser pulse signal. From the experiment and the simulation, we have convinced that the EOS can be a non-destructive diagnostic tool for low energy beam for XFEL.
Joon Hee Jang,Hee Jung Kim,Hee-Joon Kim,Chul Hoon Kim,주태하,조대원,윤민중 대한화학회 2007 Bulletin of the Korean Chemical Society Vol.28 No.11
Photophysical properties of a newly-synthesized porphyrin derivative, trans-bis(ferrocene carboxylato)(5,10,15,20-tetraphenylporphyrinato)tin(IV) [Sn(TPP)(FcCOO)2] were investigated by means of steady-state and fs-time resolved laser spectroscopic techniques, and compared with those of a standard molecule, trans-dichloro(5,10,15,20-tetraphenyl-porphrinato)tin(IV) [Sn(TPP)Cl2]. The fluorescence spectrum of Sn(TPP)(FcCOO)2 was observed to exhibit dual emission bands originating from the S2-state and the S1-state, which was greatly quenched as compared to those of Sn(TPP)Cl2. The fs-time resolved fluorescence and transient absorption spectroscopic measurements revealed that the fluorescence quenching is due to formation of the long-lived charge transfer state by intramolecular electron transfer from ferrocene to the S2-excited SnTPP in addition to the enhanced non-radiative deactivation processes.