2017 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 involved conformational characterization of the conjugated polymer polyfluorene by optical micro-spectroscopy, with the aim to reveal the origin of the green emission band on single-chain level. Further topics included nanoscale characterization of fluorescence upconversion by triplet-triplet annihilation, in particular the effect of plasmon enhancement on triplet-triplet energy transfer and triplet exciton diffusion. Also, work proceeded on polarization fluorescence spectroscopy of single particles of Photosystem I (PS I) enhanced by localized plasmon of gold nanorod substrate with the aim to identify emitting species in the PS I complex at room temperature.
Collaborations initiated within the project have been continuing on the topics of single-particle characterization of spectroscopic properties of I-III-IV semiconductor nanocrystals with an emphasis on revealing the properties and mechanism of band-edge emission in newly synthesized core-shell particles. New collaborative research was started on the topic of molecular film alignment during photopolymerization, with the aim to revel the alignment mechanism by monitoring diffusion of single luminescent quantum dots dispersed in the film precursors.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Single chains of polyfluorene were studied in different good- or poor-solvent polymer matrices, in polymer solutions, or exposed to different solvents. The experiments were complemented with measurements of fluorescence lifetime and quantum yield, and with molecular dynamics calculations. The results reveal two spectral forms in the region of the green emission, a vibrationally-resolved type around 500 nm, and broad structureless type between 520 and 575 nm. These types were assigned to H-aggregates and charge-transfer complexes.
Within the topic of fluorescence upconversion, plasmonic nanostructures composed of Ag nanowires combined with an upconversion system PtOEP donor and DPA acceptor molecules dispersed in PMMA film were studied by simultaneous upconversion and phosphorescence microscopic imaging. The emission intensity can be enhanced up to 15 fold in the vicinity of hotspots formed by the Ag nanowires, due to plasmon enhancement of Dexter energy transfer within the system.
Polarization spectroscopy of single particles of PS I at room temperature together with quantum chemical calculations helped to identify potential candidates of chlorophyll monomers as the short-wavelength emitters at 687 nm and chlorophyll dimers as the long-wavelength emitters at 717 nm.
The research on I-III-VI group semiconductors concentrated on AgInS2/GaSx core/shell structures which show an intense narrow-band emission. Single-particle spectroscopy showed that the linewidth of this band-edge PL was 80.0 meV, comparable with industry-standard II-VI semiconductor quantum dots.
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| Strategy for Future Research Activity |
This year, work will continue on conformation and photophysical properties of conjugated polymers upon different modes of excitation and different external stimuli. Effort will be concentrated on characterization of single chains or nanoparticles of polyfluorene derivatives by simultaneous confocal and atomic force microscopy (afm). The aim of the study will be mechanical manipulation of the conformation by the afm tip, and measurement of the resulting variations of the photophysical properties. Apart from polyfluorene, other conjugated polymers such as polythiophene or polyphenylene vinylene will be explored.
Within the topic of fluorescence upconversion, research will concentrate on uncovering the mechanism of plasmon enhancement of Dexter-type energy transfer, which is a phenomenon that has not been know so far. This will include design of systems enabling precise control of the geometry of the hot spots, as well as plasmonic materials.
The collaborative research on the I-III-IV semiconductor nanocrystals will continue towards achieving pure band-edge emission. Within the topic of the of molecular film alignment during photopolymerization, the effort will concentrate on monitoring monomer as well as polymer diffusion in the vicinity of a photomask to reveal the alignment mechanism.
As a new topic, photoluminescence and electroluminescence of nanocrystals of halide perovskites will be studied on single particle level. The problems to be addressed include mechanism and origin of blinking, photodegradation, and efficiency limiting factors in electroluminescence.
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