• Title/Summary/Keyword: triplet state

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Efficiency Factors of Singlet Oxygen Generation from Core-Modified Expanded Porphyric : Tetrathiarubyrin in Ethanol

  • Ha, Jeong Hyeon;Jeong, Guk Yeong;Kim, Min Seon;Lee, Yang Hun;Sin, Gu;Kim, Yong Rok
    • Bulletin of the Korean Chemical Society
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    • v.22 no.1
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    • pp.63-67
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    • 2001
  • The photophysical properties and the singlet oxygen generation efficiency of tetrathiarubyrin have been investigated to elucidate the possibility of its use as a photodynamic therapy (PDT) photosensitizer by steady-state and time-resolved spectroscopic methods. The observed photophysical properties were affected by various molecular aspects, such as extended ${\pi}conjugation$, structural distortion, and internal heavy atom. The steady-state electronic absorption spectrum was red-shifted due to the extended $\pi-conjugation$, and the spin orbital coupling was enhanced by the structural distortion and the internal heavy atom effect. As a result of the enhanced spin orbital coupling, the triplet quantum yield increased to 0.90 $\pm$ 0.10 and the triplet state lifetime was shortened to 7.0 $\pm$ 1.2 ${\mu}s$. Since the triplet state decays at a relatively faster rate, the efficiency of the oxygen quenching of the triplet state decreases. The singlet oxygen quantum yield was estimated to be 0.52 $\pm$ 0.02, which is somewhat lower than expected. On the other hand, the efficiency of singlet oxygen generation during the oxygen quenching of triplet state, $f{\Delta}^T$, is near unity. Such high efficiency of singlet oxygen generation can be explained by the following two possible factors: The hydrogen bonding of ethanol which impedes the deactivation pathway of the charge transfer complex with oxygen to the ground state, the less probability of the aggregation formation.

Design of Efficient Electroluminescent lanthanide(Ⅲ) Complexes

  • Yu, Bo Ra;Kim, Hwa Jung;Park, No Gil;Kim, Yeong Sik
    • Bulletin of the Korean Chemical Society
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    • v.22 no.9
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    • pp.1005-1008
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    • 2001
  • The lanthanide complexes have been anticipated to exhibit high efficiency along with a narrow emission spectrum. Photoluminescence for the lanthanide complex is characterized by a high efficiency since both singlet and triplet excitons are involve d in the luminescence process. However, the maximum external electroluminescence quantum efficiencies have exhibited values around 1% due to triplet-triplet annihilation at high current. Here, we proposed a new energy transfer mechanism to overcome triplet-triplet annihilation by the Eu complex doped into phosphorescent materials with triplet levels that were higher than singlet levels of the Eu complex. In order to show the feasibility of the proposed energy transfer mechanism and to obtain the optimal ligands and host material, we have calculated the effect depending on ligands as a factor that controls emission intensity in lanthanide complexes. The calculation shows that triplet state as well as singlet state of anion ligand affects on absorption efficiency indirectly.

Density Functional Theory Calculation of Molecular Structure and Vibrational Spectra of Dibanzofuran in the Ground Lowest Triplet State.

  • Lee, Sang Yeon
    • Bulletin of the Korean Chemical Society
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    • v.22 no.6
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    • pp.605-610
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    • 2001
  • The molecular geometries and harmonic vibrational frequencies of dibenzofuran in the ground and lowest triplet state have been calculated using the Hartree-Fock and Becke-3-Lee-Yang-Parr(B3LYP)density functional methods with the 6-31G basis set. Upon the excitation to the lowest triplet state, the molecular structure retains the planar form but distorts from a benzene-like to a quinone-like form in skeleton. Scaled vibrational frequencies for the ground and lowest triplet state obtained from the B3LYP calculation show excellent agreement with the available experimental data. A few vibrational fundamentals for both states are newly assigned based on the B3LYP results.

INVESTIGATION OF TRIPLET STATE AND SINGLET OXYGEN DYNAMICS OF BENZOPHENONE IN POLAR AND NONPOLAR SOLUTIONS WITH TIME-RESOLVED TWO-COLOR THERMAL LENSING METHOD

  • Ha, Jeong-Hyon
    • Journal of Photoscience
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    • v.3 no.3
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    • pp.141-145
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    • 1996
  • The heat generated by nonradiative decay dynamics induces thermal lens effect. From such an effect, photodynamic properties of solutions can be investigated with two-color pulsed thermal lens experiments which have the time resolution of down to nanoseconds. In this study, using nanosecond two-color thermal lens method, we investigated the triplet state of benzophenone and the singlet oxygen state dynamics in various oxygen concentration solvents. The measured triplet state lifetimes, singlet oxygen relaxation times and singlet oxygen formation quantum yields are in good agreement with the reference values. From these parameters the existence of the triplet exciplex formation between benzophenone and benzene is proved, and it is also suggested that the relaxations of triplet states of benzophenone undergo coupled dynamics with some of singlet oxygens in oxygen-rich conditions.

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Photophysical Efficiency Factors of Singlet Oxygen Generation from Core-modified Trithiasapphyrin Derivatives

  • Ha, Jeong-Hyon;Kim, Min-Sun;Park, Yong-Il;Ryu, Shin-Hyung;Park, Mi-Gnon;Shin, Koo;Kim, Yong-Rok
    • Bulletin of the Korean Chemical Society
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    • v.23 no.2
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    • pp.281-285
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    • 2002
  • The photophysical properties and the singlet oxygen generation efficiencies of meso-tetraphenyl-trithiasapphyrin $(S_3TPS)$ and meso-tetmkis(p-methoxy phenyl)-trithiasapphy rin ((p-MeO)-$S_3TPS$) have been investigated, utilizing steady-state and time-resolved spectroscopic methods to elucidate the possibility of their use as photosensitizers for photodynamic therapy (PDT). The observed photophysical properties were compared with those of other porphyrin-like photosensitizers in geometrical and electronic structural aspects, such as extended ${\pi}$ conjugation, structural distortion, and internal heavy atoms. The steady-state electronic absorption and fluorescence spectra were both red-shifted due to the extended ${\pi}$-conjugation. The fluorescence quantum yields were measured as very small. Even though intersystem crossing rates were expected to increase due to the increment of spin orbital coupling, the triplet quantum yields were measured as less than 0.15. Such characteristics can be ascribed to the more enhanced internal conversion rates compared with the intersystem crossing rates. Furthermore, the triplet state lifetimes were shortened to -1.0 ${\mu}s$ as expected. Therefore, the singlet oxygen quantum yields were estimated to be near zero due to the fast triplet state decay rates and the inefficient energy transfer to the oxygen molecule as well as the low triplet quantum yields. The low efficiencies of energy transfer to the oxygen molecule can be attributed to the lower oxidation potential and/or the energetically low lying triplet state. Such photophysical factors should be carefully evaluated as potential photosensitizers that have extended ${\pi}$-conjugation and heavy core atoms synthesized for red-shifted absorption and high triplet state quantum yields.

A Theoretical Study of the Formation of Benzene Excimer: Effects of Geometry Relaxation and Spin-state Dependence

  • Kim, Dongwook
    • Bulletin of the Korean Chemical Society
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    • v.35 no.9
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    • pp.2738-2742
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    • 2014
  • Geometry relaxation effects on the formation of benzene excimer were investigated by means of ab initio calculation at SOS-CIS($D_0$)/aug-cc-pVDZ level. In the case of T-shaped dimer configuration, intermolecular interactions in the excited states are found to be nearly the same as those in the ground state and structural deformations are limited within a single molecule; the geometry relaxation effects are then negligible and singlet-triplet energy gap remains constant. As for face-to-face eclipsed dimer, on the other hand, both molecules undergo structural change. As a result, intermolecular interactions in the excited states are significantly different than those in the ground state. Although the intermolecular distances obtained from potential energy curve calculation with frozen molecular structures are in qualitative agreement, the excited-state binding energies are notably overestimated with respect to those at optimized structures. In particular, the effects are calculated to be larger in $T_1$ state and hence singlet-triplet energy gap, which reduces markedly in this configuration, is underestimated without relaxation.

Cycloaddition Reaction on 1,4,5,8-Tetraazaphenanthrene Photoexcited Triplet State to Some Olefins

  • Park, Seung-Ki;Shim, Sang-Chul
    • Bulletin of the Korean Chemical Society
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    • v.8 no.1
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    • pp.27-30
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    • 1987
  • Photocycloaddition of 1,4,5,8-tetraazaphenanthrene to olefins proceeds through a biradical triplet-state intermediate as proven by the photoproduct stereochemistry, quantum yield measurements, sensitization, quenching, and fluorescence and phosphorescence quenching studies.

Photodynamics of an excited triplet state in the presence of molecular oxygen cluster

  • Nishimura, Yoshinobu
    • Rapid Communication in Photoscience
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    • v.2 no.3
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    • pp.72-75
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    • 2013
  • Bulk nanobubble is one of the nanoscopic gaseous state found in the solution. We measured transient absorption spectra of eosin Y in the excited triplet state ($^3EY^{2-*}$) to elucidate differences in the dissipation process of the bulk nanobubble of oxygen molecule at air pressure. The time dependence of the oxygen dissipation process was classified three time domains (P1, P2 and P3). The comparison of ordinary bubbling method gave different results at P3 in contrast to similar results at P1 and P2, indicating the existence of characteristic dissolving state in the case of nanobubble.

Energy Relaxation Dynamics of Excited Triplet States of Directly Linked Zn(II)Porphyrin Arrays

  • Song, Nam-Woong;Cho, Hyun-Sun;Yoon, Min-Chul;Aratani, Naoki;Osuka, Atsuhiro;Kim, Dong-Ho
    • Bulletin of the Korean Chemical Society
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    • v.23 no.2
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    • pp.271-276
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    • 2002
  • The energy relaxation dynamics of the lowest excited singlet and triplet states of the Zn(II)porphyrin monomer and its directly linked arrays were comparatively investigated with increasing the number of porphyrin moieties. While the fluorescence decay rates and quantum yields of the porphyrin arrays increased with the increase of porphyrin units, their triplet-triplet (T-T) absorption spectra and decay times remained almost the same. The difference in the trends of energy relaxation dynamics between the excited singlet and triplet states has been discussed in view of the electronic orbital configurations.