2015 Fiscal Year Annual Research Report
分子集団の協同的光応答の分子レベル解明および動的制御
| 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, 理工学研究科, 教授 (50361746)
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| Co-Investigator(Kenkyū-buntansha) |
平田 修造 東京工業大学, 理工学研究科, 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 and oligomers on single-chain level by optical micro-spectroscopy, with the aim of simultaneous measurement and control of the conformation and photophysics by atomic force microscopy. Further, as new topics within the frame of different excitation modes, work began and progressed on nanoscale characterization of fluorescence upconversion by triplet-triplet annihilation where a method of direct microscopic measurement of triplet exciton diffusion was developed, and on study of enhancement of excitation energy transfer within an array of conjugated molecules by localized plasmon of a gold nanoparticle, where the initial observations point to a large enhancement factor on the order of 100.
In addition, several collaborations were initiated within the project. Apart from a collaborative research on the triplet-triplet annihilation based fluorescence upconversion, work started on single-particle characterization of spectroscopic properties of I-III-IV semiconductor nanocrystals by dual-mode excitation, and on efforts to explore the possibility of single-molecule detection of a photoresponsive conjugated molecule which changes its emission color depending on the rigidity of its environment.
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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
The study of the conformation of conjugated polymers and oligomers on single-chain level progressed mainly according to the research plan. It was found that large spontaneous spectral changes in polyfluorenes that were assigned to conformational changes depend strongly on the rigidity (glass transition temperature) of the surrounding environment. These findings were supplemented by ensemble level experiments in which change of the color of the polyfluorene was induced by mechanical stretching of a free-standing film. On the other hand, the simultaneous measurement and control of the conformation by atomic force microscopy (afm) was delayed and has not yet brought positive results. It turned out that imaging of the sample topology on a quartz cover slip substrate was unexpectedly difficult due to increased noise and surface roughness. Work is now in progress to solve the problems by using different cantilevers, covering the quartz surface with a thin layer of mica, and further reducing vibrations.
The work on the new topics of upconversion and plasmon-enhanced energy transfer proceeded as planned. The newly developed microscopic method yielded the first results on direct measurement of triplet exciton diffusion length, and shows an excellent potential in characterization of important photophysical steps in the upconversion process. After initial struggles, the experiments on plasmon enhanced energy transfer revealed surprisingly strong effect of the plasmon and will bring new insight into the mechanism.
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| Strategy for Future Research Activity |
This year, work will continue on the study of photophysical properties of conjugated polymers upon different modes of excitation. Effort will be concentrated on the long overdue photophysical characterization of single chains or single nanoparticles by simultaneous confocal and afm microscopy, with the aim of mechanical manipulation of the conformation by the afm tip. Apart from the currently studied BDOH-PF, other polyfluorene derivatives as well as topological varieties of polythiophene will be explored.
Within the topic of nanoscale characterization of fluorescence upconversion, the research will concentrate on the dependence of the exciton diffusion length on the chemical composition of the emitter material, on its state and on the dimensionality (1-D systems prepared by electrospinning). The topic of plasmon-enhanced energy transfer will continue by further characterization of the phenomena of energy transfer within a molecular assembly adsorbed on a single gold nanorod and on the theoretical interpretation of the results, and on exploring other configurations such as enhancement of energy transfer between 1-D (Au nanorod) and 2-D (molecular layer) systems on single particle level.
The collaborative research on the I-III-IV semiconductor nanocrystals will continue on a relationship between single-particle parameters such as spectra and fluorescence blinking and macroscopic parameters such as quantum yield and lifetimes. With the advancement of synthetic techniques, work will also begin on characterization of nanocrystals with a direct bandgap transitions.
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Research Products
(13 results)
