2016 Fiscal Year Annual Research Report
Molecular-level study and control of cooperative photoresponse of molecular complexes
| Project Area | Application of Cooperative-Excitation into Innovative Molecular Systems with High-Order Photo-functions |
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| Project/Area Number |
26107014
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
VACHA Martin 東京工業大学, 物質理工学院, 教授 (50361746)
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| Co-Investigator(Kenkyū-buntansha) |
平田 修造 東京工業大学, 物質理工学院, 助教 (20552227)
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| Project Period (FY) |
2014-07-10 – 2019-03-31
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| Keywords | molecular complexes / single molecule studies |
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| Outline of Annual Research Achievements |
The research in the past year concentrated on conformational characterization of conjugated polymers on single-chain level by optical micro-spectroscopy, with the aim of uncovering the effect of environment on the chain conformation and spontaneous conformation dynamics. Further topic within the frame of different excitation modes involved nanoscale characterization of fluorescence upconversion by triplet-triplet annihilation with an emphasis on revealing the nanoscale characteristics of triplet exciton diffusion and plasmon-enhanced upconversion, the study of plasmon enhancement of Foerster excitation energy transfer between small conjugated molecules attached to a gold nanoparticle, and as a new topic polarization fluorescence spectroscopy of single particles of Photosystem I enhanced by localized plasmon of gold nanorod substrate.
In addition, collaborations initiated within the project have been continuing on the topics of the triplet-triplet fluorescence upconversion, on single-particle characterization of spectroscopic properties of I-III-IV semiconductor nanocrystals, and on single-molecule detection of a photoresponsive conjugated molecule which changes its emission spectrum upon the effect of external mechanical stimuli.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
In the study of conformation of conjugated polymers, for different derivatives of polyfluorene it was found that the large variety of spectral forms reflects different types of intrachain aggregation and that it depends strongly on polarity and glass-transition temperature of polymer matrix. For the polymer in solution it was demonstrated that changes from good to poor solvent cause complete and reversible transformation of emission color from blue to green.
In the work on plasmon-enhanced energy transfer (FRET) hybrid nanostructures composed of a gold nanorod and donor and acceptor molecules were studied on the level of a single particle by simultaneous dark-field and fluorescence microscopy. The emission of acceptor molecules could be controllably modulated by polarization, thus enabling a selective turn-on of the FRET process. Numerical simulations showed an increase of FRET efficiency by a factor of 65.
The work on fluorescence upconversion concentrated on nanoscale triplet exciton diffusion. Hybrid particles of donor molecules attached to inorganic spheres were dispersed in polycrystalline or amorphous films of acceptor molecules. Detection of microscopic images of phosphorescence from donor and upconversion from acceptor enabled direct observation of triplet diffusion.
The work on single-particle photoluminescence (PL) of (AgIn)xZn2(1-x)S2 nanocrystals showed that the PL band is inhomogeneously broadened due to size distribution. Excitation with two lasers revealed coexistence of two defect states within one particle and enabled optical control of PL blinking.
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| Strategy for Future Research Activity |
This year, work will continue on the study of conformation and photophysics of conjugated polymers upon different excitations and different external stimuli, by simultaneous confocal and afm microscopy. Apart from polyfluorene, topological forms of conjugated polymers such as polythiophene or polyphenylene vinylene will be explored.
Within the topic of fluorescence upconversion, research will continue on exciton diffusion with regards to the chemical composition of the acceptor, to its state and dimensionality. The effect of plasmon enhancement of upconversion will be investigated on samples containing silver or gold nanoparticles embedded in the upconversion system. Plasmon-enhanced energy transfer will concentrate on design of systems enabling precise control of the distance between the donor and acceptor molecules, such as multiple-layer samples with a polymer spacer layers. The collaborative research on the I-III-IV semiconductor nanocrystals will continue towards achieving pure bandgap emission. Within the topic of the photoresponsive conjugated molecules, work will continue on novel compounds synthesized with the aim to shift the absorption and emission spectra towards lower energies and to increase the quantum yield, with the final goal to achieve reliable single-molecule characterization.
As a new topic, polarization fluorescence spectroscopy of single particles of Photosystem I enhanced by localized plasmon of gold nanorod substrate will be carried out with the aim of revealing the structural origin of long-wavelength chlorophyll emission in these systems.
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