Persistent Hole Burning of Zinc Porphyrin with Energy and Electron Transfer Mechanisms

報告番号: 甲10574 ; 学位授与年月日: 1994-03-29 ; 学位の種別: 課程博士 ; 学位の種類: 博士(工学) ; 学位記番号: 博工第3231号 ; 研究科・専攻: 工学系研究科化学エネルギー工学専

エネルギ-および電子移動機構による亜鉛ポルフィリンの永続的ホ-ルバ-ニング

University of Tokyo (東京大学

Single-Photon Emission Behavior of Isolated CdSe/ZnS Quantum Dots Interacting with the Localized Surface Plasmon Resonance of Silver Nanoparticles

To reveal the exciton dynamics, particularly multiexciton dynamics in single colloidal CdSe/ZnS quantum dots (QDs) interacting with the localized surface plasmon resonance (LSPR) of silver nanoparticles (AgNPs), we investigated the single-photon emission behavior in the fluorescence from the single QDs using a single-molecule spectroscopy technique in combination with a femtosecond-pulsed laser excitation. By applying simultaneous measurements of the photon-correlation (photon antibunching), the fluorescence intensity, and the fluorescence lifetime to the single QD near AgNPs, we revealed that the probability of single-photon emission strongly depended on the fluorescence lifetime; that is, the probability of single-photon emission decreased when the lifetime was shorter than subnanoseconds. On the basis of the estimation of both radiative and nonradiative decay rates enhanced by the LSPR, the following mechanism was suggested. In the absence of AgNPs, multiple excitons generated by a high-power excitation lead to single-photon emission via nonradiative Auger recombination process between the excitons. In the presence of AgNPs, even when the excitation power is low, multiple excitons are initially generated in a single QD by the enhanced electromagnetic field of the AgNPs’ LSPR. Subsequently, a portion of these excitons radiatively decay via plasmon, that is, the radiative decay rate enhanced by LSPR competes with the Auger recombination process. When the enhanced radiative decay rate is faster than that of the Auger process, multiphoton emission can be observed. Therefore, a decrease in the probability of single-photon emission is observed when the fluorescence lifetime is shortened. This result will improve our understanding of fluorescence enhancement by the LSPR of metal nanostructures, assist in the creation of effective single-photon sources, and allow for the utilization of the multiexcitons in QDs for optoelectronic applications

Group 14 Dithienometallole-Linked Ethynylene-Conjugated Porphyrin Dimers

The considerably conjugated π systems of the group 14 dithienometallole-linked ethynylene-conjugated porphyrin dimers (<b>1M</b>s) were described based on comprehensive experimental and theoretical studies. The electronic absorption spectra of <b>1M</b> displayed a large splitting in the Soret band and a red-shifted Q-band, indicating that the dithienometallole spacer was effective in facilitating the porphyrin–porphyrin electronic coupling. Torsional planarization behaviors of <b>1M</b> were observed in the time-resolved fluorescence spectra. Density functional theory (DFT) calculations revealed that the dithienometallole spacer is an ideal partner for the ethynylene-conjugated porphyrin to produce fully delocalized highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels due to their similar HOMO and LUMO levels. Finally, <b>1M</b> exhibited a strong propensity for the quinoidal–cummulenic conjugation in the dithienometallole spacer when in a photoexcited state