2015 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 |
Research in the past year concentrated on conformational characterization of conjugated polymers and oligomers on individual chain level by single molecule polarization microscopy and spectroscopy. The main target material was a derivative of polyfluorene, BDOH-PF, which was previously shown to exhibit strongly conformational dependent photophysical properties in both photoluminescence and electroluminescence. Apart from photophysical characterization in different polymer matrices and upon mechanical deformation, the study also involved attempts at simultaneous characterization by confocal and atomic force microscopy (afm).
In addition, collaborations with domestic and overseas groups were initiated within the project, with the aim to characterize the effect of topology of conjugated polymer chains on their photophysics. Change of the topology from linear to cyclic 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. Most of the results were obtained on cyclic and linear poly(phenylene vinylene) (PPV) while initial characterization has been carried out for polythiophene. Similar effects are expected to govern the photophysics of cyclic conjugated oligomers such as cyclo-paraphenylene (CPP), which has also been studied on single-molecule level.
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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 single-chain conformation of conjugated polymers and its dynamics proceeded mainly according to the research plan. It was found that large spontaneous spectral changes in BDOH-PF depend strongly on the rigidity (glass transition temperature) of the surrounding matrix providing further evidence for the explanation of the green emission band in polyfluorenes as due to interchain aggregation.
The simultaneous measurement and control of the conformation by atomic force microscopy (afm) was delayed and has not yet brought reliable and reproducible results. It was found 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 collaborative work on the effect of topology of conjugated polymers on their photophysics proceeded mainly as planned. It was found that the topology of PPV strongly affects its chain conformation which is close to a ring for cyclic PPV and an extended coil for the linear PPV. Despite the large difference between the conformations, both topological forms show surprisingly similar spectral properties, and this observation was attributed to the relatively large molecular weight. On the other hand, the work on single molecules of the macrocyclic CPP revealed a variety of single-molecule spectral shapes and positions, which pointed to an inhomogeneous nature of the ensemble spectrum.
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| Strategy for Future Research Activity |
This year, the study of photophysical properties of conjugated polymers in relation to their conformation will continue. Emphasis will be put on the long overdue photophysical characterization of single chains or single nanoparticles of BDOH-PF by simultaneous confocal and afm microscopy. 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. The results are expected to provide the first direct evidence of the origin of the green band emission in polyfluorenes. Apart from the currently studied BDOH-PF, other polyfluorene derivatives will be explored. Depending on the success of the simultaneous confocal and afm experiments, next stage involving single chain/particle electroluminescence study using biased afm tip as an electrode will be considered.
At the same time, work will continue on single chain photophysical characterization of the topology effect of conjugated polymers. Cyclic and linear forms of polythiophene will be studied in a similar way as the PPV species. Apart from the topology effect, molecular weight dependence towards shorter chains will be considered to reveal the critical size of the chains at which the topological effects start playing a dominant role. Further, in the study of the CPP macrocycles, the single-molecule results will be complemented by theoretical calculations involving distorted conformations with the aim to get insight into the basic photophysical properties of this new class of conjugated molecules.
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| Causes of Carryover |
本研究に使用した消耗品が研究計画していたより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、原子間力顕微鏡での振動の問題を解決するためにカンチレバー、基板、などの消耗品を購入する予定である。
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Research Products
(8 results)
