• Bulletin of the Korean Chemical Society
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• 제12권3호
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• pp.245-247
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• 1991

• Rapid Communication in Photoscience
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• 제3권4호
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• pp.85-87
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• 2014

We studied the characteristics of emissive state of the first (p-G1) and second (p-G2) generation of phenylacetylene dendrimers bearing stilbene as a core by using time-resolved fluorescence spectroscopy in cyclohexane (c-Hex) and N, N-dimethylformide (DMF), which are nonpolar and polar solvents, respectively. Time-dependent red-shift of emission spectra p-G2 both in c-Hex and DMF was observed in comparison with p-G1. Besides, the time constant of red-shift of spectra was found to be larger in DMF than in c-Hex. This indicates that the emissive state of p-G2 has a polar character in DMF as a result of charge delocalization from core to peripheral dendrons followed by stabilization of emissive state.

• Nuclear Engineering and Technology
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• 제25권4호
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• pp.548-551
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• 1993

원자력 산업의 변환공정에서 발생하는 폐수용액중의 우라늄 농도를 레이저 유발형광법을 사용하여 쉽게 측정할 수 있는 새로운 분석방법을 개발하였다. 실험 결과 시료의 약 10배 이상의 부피로 4M-인산용액을 첨가함으로써 효율적으로 형광 quencher의 영향을 배제시킬 수 있었으며, 폐액 시료에서의 우라늄 농도 3.0$\times$$10^{-6}$－6.0$\times$$10^{-5}$ M U $O_2$$^{2＋}$의 범위에서 농도에 대한 형광강도의 직선성이 우수하였다.

• Bulletin of the Korean Chemical Society
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• 제35권3호
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• pp.881-885
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• 2014

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 $S_2{\rightarrow}S_1$ internal conversion in the reaction product keto isomer and that the ESIPT occurs from the enol isomer in $S_1$ state to the keto isomer in $S_2$ state.

• 청정기술
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• 제19권3호
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• pp.327-332
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• 2013

광학 및 형광 현미경을 이용한 실시간 촉매 모니터링 기술을 활용하여 C5 파라핀과 올레핀의 방향족화 반응 중 H-ZSM-5 촉매 표면에서 발생하는 코크 형성 과정을 시간별, 촉매 위치별로 관찰하였다. 실시간 자외-가시광 분광현미경(in-situ UV-vis microspectroscopy) 실험을 통해 반응 중 촉매 표면에서 발생하는 코킹 현상에 대한 정보를 실시간으로 얻을 수 있었으며, 그 결과, 결정의 위치와 반응물의 종류에 따라 코크 형성이 크게 달라짐을 확인하였다. 실시간 공초점형 형광현미경(in-situ confocal fluorescence microscopy) 연구에서는, 488 nm 레이저에 의해 형광을 나타내는 화학종들은 높은 분포로 결정의 중앙부분에 존재하며, 561 nm 레이저에 의해 형광을 발현하는 화학종들은 촉매 결정의 외곽으로 이동하는 것을 관찰하였다. 이러한 결과는, 코크 전구체의 크기에 따라 형광 발현 현상이 다르며, 따라서, 촉매의 위치에 따라 다른 종류의 코크 전구체가 존재한다는 것을 시사한다.

• 방사성폐기물학회지
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• 제18권4호
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• pp.497-508
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• 2020

In the geochemical field, the chemical speciation of hexavalent uranium (U(VI)) has been widely investigated by performing measurements to determine its luminescence properties, namely the excitation, emission, and lifetime. Of these properties, the excitation has been relatively overlooked in most time-resolved laser fluorescence spectroscopy (TRLFS) studies. In this study, TRLFS and continuous-wave excitation-emission matrix spectroscopy are adopted to characterize the excitation properties of U(VI) surface species that interact with amorphous silica. The luminescence spectra of U(VI) measured from a silica suspension and silica sediment showed very similar spectral shapes with similar lifetime values. In contrast, the excitation spectra of U(VI) measured from these samples were significantly different. The results show that distinctive excitation maxima appeared at approximately 220 and 280 nm for the silica suspension and silica sediment, respectively.

• Journal of Photoscience
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• 제2권1호
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• pp.19-25
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• 1995

Picosecond time-resolved and static protein fluorescence spectra and absorption spectra of octopus rhodopsin, a photorecepting protein, are measured and compared with those of bacteriorhodopsin, a photon-induced proton pumping protein, to understand the protein conformations and functions of octopus rhodopsin and its deprotonated photocycle intermediate. The bluer and weaker absorption of retinal indicates that octopus rhodopsin is better in thermal noise suppression but less efficient in light harvesting than bacteriorhodopsin. The protein fluorescence of octopus rhodopsin shows the characteristic of Trp only and the uantum efficiency and lifetime variations may result primarily from variations in the coupling strength with the retinal. The stronger intensity by four times and larger red shift by 12 nm of fluorescence suggest that octopus rhodopsin has more open and looser structure compared with bacteriorhodopsin. Fluorescence decay profiles reveal two decay components of 300 ps (60%) and 2 ns (40%). The deprotonation of protonated Schiff's base increases the shorter decay time to 500 ps and enhances the fluorescence intensity by 20%. The fluorescence and its decay time from Trp residues near retinal are influenced more by the deprotonation. The increase of fluorescence intimates that protein structure becomes loosened and relaxed further by the deprotonation of protonated Schiff's base. The driving force of sequential changes initiated by absorption of a photon is too exhausted after the deprotonation to return the intermediate to the ground state of the begun rhodopsin form.

• Bulletin of the Korean Chemical Society
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• 제19권7호
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• pp.747-753
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• 1998

The phoisomerization process of symmetric carbocyanine dyes such as 3,3'-diethyloxadicarbocyanine iodide (DODCI), 3,3'-diethylthiadicarbocyanine iodide (DfDCI), 1,1'-diethyl-2,2'-dicarbocyanine iodide (DDI), 1,1'-diethyl-2,2'-carbocyanine iodide (DCI), and cryptocyanine (1,1'-diethyl-4,4'-carbocyanine) iodide (CCI) have been studied by measuring the steady state and time resolved fluorescence spectra and the ground-state recovery profiles. The steady-state fluorescence spectrum of photoisomer as a function of concentration and excitation wavelength provides the evidence that the fluorescence of photoisomer is formed by the radiative energy transfer from the normal form and the quantum yield for the formation of photoisomer is increased by decreasing the excitation wavelength. The fluorescence decay profiles have been measured by using the time correlated single photon counting (TCSPC) technique, showing a strong dependence on the concentration and the detection wavelength, which is due to the formation of excited photoisomers produced either by the radiative energy transfer from the non-nal form or by absorbing the 590 nm laser pulse. We first report the fluorescence decay time of photoisomers for these cyanine dyes. The experimental results are explained by introducing the semiempirical calculations. The ground state recovery profiles of DTDCI, DDI, and CCI normal forms have been measured, showing that the recovery time from the singlet excited state is similar with the fluorescence decay time.

• 한국고분자학회지:고분자과학과기술
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• 제25권2호
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• pp.147-150
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• 2014

• Rapid Communication in Photoscience
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• 제4권3호
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• pp.70-72
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• 2015

Oligomers of p-phenylene vinylene and its derivatives have drawn much attention due to their unusual emission characteristics of showing increased emission when they form into nanoparticles. We have investigated the optical properties of the oligo-(p-phenylene vinylene) and its cyano-substituted derivatives in solution and in nanoaggregate media by femtosecond and picosecond time resolved fluorescence as well as stationary spectroscopies. All the spectroscopic data are consistent with the conclusion that the cyano substitution on the ${\beta}$-position of oligo-(p-phenylene vinylene) leads to breakage of the otherwise planar structure of cyano-unsubstituted molecules, which opens up an extremely efficient, as fast as 100 fs, non-radiative relaxation channel of the excited state. Formation of the nanoaggregates reverts the effect to make the molecules planar and to block the non-radiative relaxation channel. Therefore, concerning the applications in organic electroluminescent devices and organic light emitting diodes, substitution by the cyano group is not advantageous, although such modification should be useful in respect of controlling fluorescence intensity in different media.