| 研究領域 | 高次複合光応答分子システムの開拓と学理の構築 |
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| 研究課題/領域番号 |
26107014
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| 研究機関 | 東京工業大学 |
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研究代表者 |
VACHA Martin 東京工業大学, 理工学研究科, 教授 (50361746)
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| 研究分担者 |
平田 修造 東京工業大学, 理工学研究科, 助教 (20552227)
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| 研究期間 (年度) |
2014-06-27 – 2019-03-31
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| キーワード | molecular complexes / single-molecule studies |
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| 研究実績の概要 |
The research involves molecular assemblies composed of conjugated small molecules or conjugated polymers, and concentrates on two main points, 1. Effects of different excitation modes on the excited state and conformation of the molecular assembly, and 2. Active control the conformational state and the resulting photophysical properties by external stimuli. The research in the past year concentrated mainly on the point 1., and involved the study of conformational changes of a conjugated polymer polyfluorene on a single-chain level upon excitation by linear absorption of light and by charge recombination. Both excitations lead to dramatically different photophysical properties that reflect different conformational states resulting from intramolecular aggregation. In photoluminescence, the emission spectra are dominated by either singlet excitons or by excimer-like states formed via neutral ground-state aggregates. In electroluminescence the singlet exciton emission is absent and the spectra are either due to formation of charged ground-state intramolecular aggregates or excimer-like states. In both photoluminescence and electroluminescence, thermally induced conformational dynamics of the polyfluorene chains lead to strong spectral dynamics on timescales of seconds. The experimental observations were complemented by quantum-chemical calculations which supported the existence of the different conformational states. In addition, work also began on study of plasmon-enhanced emission from conjugated polymers chemically attached to gold nanoparticles.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
1: 当初の計画以上に進展している
理由
The study of the conjugated polymer polyfluorene on a single-chain level upon excitation by linear absorption of light and by charge recombination and the resulting structural changes fits well within the frame of the research goal of the project `Molecular-level study and control of collective photoresponse from conjugated molecular complexes’. In particular, the assignment of the newly discovered single-chain spectral features to various aggregation states brings a new perspective into the problem of the parasitic green emission in polyflyorenes and is bound to attract broad attention.
Apart from the study of the effect of excitation modes on single conjugated polymer chains, work was successfully completed 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 tunable excitation source based on a supercontinuum laser. The new excitation source together with highly sensitive CCD camera and an imaging spectrograph will enable simultaneous measurement of force spectra by AFM and of fluorescence spectra on the level of single molecules over a wide spectral ranges, as well as single-molecule excitation or single-particle absorption/scattering spectra. The setup is expected to greatly contribute to the success of the point 2. of the research plan.
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| 今後の研究の推進方策 |
This year, work will continue on the study of photophysical properties of conjugated polymers upon different modes of excitation. The photophysical characterization of single chains will be done simultaneously with mechanical manipulation by an AFM tip. The polymer chains will be dispersed in a thin film of an inert soft polymer and fluorescence spectra will be recorded at different pressures of the AFM tip. Further, simultaneous electroluminescence 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 polymer chain. These experiments will provide a direct connection between the aggregation/conformation state and photophysical properties upon different excitation modes.
This year, work will begin on characterization of the topology effect in conjugated polymers. Change of the topology from linear to cyclic 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. Mechanical manipulation of the individual cyclic chains is expected to change the segment shapes and modify the selection rules for the optical transitions, thus leading to controllable appearance of novel optical features.
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