2014 Fiscal Year Annual Research Report
共役系高分子一本鎖のコンフォメーション制御による光電子物性の能動的制御
| Project/Area Number |
26287097
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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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| Project Period (FY) |
2014-04-01 – 2018-03-31
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| Keywords | conjugated polymers / photophysics / single-molecule studies |
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| Outline of Annual Research Achievements |
Within the overall research goal of ‘Active control of optoelectronic properties of conjugated polymers via control of their conformation on single chain level’, the past year was devoted mainly to the continued study of photoluminescence (PL) and electroluminescence (EL) of single polyfluorene (PF) chains confined in 1D cylinders of a phase-separated block-copolymer film template. The template film ensured both an extended conformation of the PF chains which is necessary for the EL operation and their spatial isolation which enables the addressable study if individual chains. The photophysical properties as measured by emission spectra of single PF were dramatically different in PL and EL, and these differences reflect different intramolecular aggregation processes. In PL the emission spectra are dominated by either singlet excitons or by excimers formed via neutral ground-state aggregates. In EL the singlet exciton emission is absent and the spectra are either due to formation of charged ground-state aggregates or excimers. In both photoluminescence and electroluminescence, thermally induced conformational dynamics of the polyfluorene chains leads to strong spectral dynamics on timescales of seconds. These finding shed new light on the origin of the green emission band in PF which has so far been ascribed to oxidation of the PF chains.
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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
The work on PL and EL of single PF chains confined in 1D block-copolymer cylinders fits well within the frame of the research goal of the project. The results represent the first example of a successful detection of EL from single molecules of a conjugated polymer and as such are likely to attract broad attraction both in academia and in industry where they could show direction for further development of high color purity PF derivatives. The results also challenge a long accepted interpretation of the green emission band in PF and will stimulate further research in the field.
Apart from the study of single PF chains, work began on the upgrading of an experimental setup consisting of an atomic force microscope (AFM) and a confocal microscope. The main part of the upgrade involved the implementation of a highly sensitive CCD camera together with an imaging spectrograph. The instalment of the spectroscopic setup will enable simultaneous measurement of force spectra by AFM and of fluorescence spectra on the level of single molecules. In addition, the microscope can be easily converted from a confocal mode to a wide-field imaging mode, thus increasing the universality of the system, and enabling advanced single molecule characterization using defocused imaging, super-resolution localization, etc.
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| Strategy for Future Research Activity |
This year, work will further continue on the photophysical properties of PF chains. To provide further support for the interpretation of the PL and EL spectra, as well as to proceed in the direction of active control of the photophysical properties, the photophysical characterization of single chains will be done simultaneously with mechanical manipulation by an AFM tip. In the first step, the PF chains will be dispersed in a soft polymer thin film and PL spectra will be recorded at different pressures of the AFM tip. In the next step, simultaneous EL spectroscopy and mechanical manipulation will be attempted by using a biased metallic AFM tip that would work both to apply pressure and to inject electrons into the PF chain.
At the same time, work will begin on single chain photophysical characterization of the topology effect of conjugated polymers. Change of the topology from linear chains to cyclic (ring) chains together with varying chain size is expected to bring changes to the size and shape of conjugated segments that comprise the conjugated polymer, and consecutively to the symmetry selection rules for the optical transitions and to the extent of the exciton mobility on the chain. The latter will be also affected by the absence of chain ends on the cyclic polymers. All these properties will be reflected in the fluorescence spectra, and excitation and emission anisotropies. As first examples, cyclic and linear chains of poly(phenylene vinylene) and polythiophene will be studied.
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| Causes of Carryover |
共焦点顕微鏡用分光システムが計画していたより安価で購入できた、また消耗品等も研究計画よりも安価で購入できたため、次年度使用額が生じた。
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| Expenditure Plan for Carryover Budget |
次年度使用額の主な使用計画として、共役系高分子が紫外線領域で効率良く励起できるレーザー光源の購入など、物品費として使用する予定である。
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