2017 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
|
|---|
| Research Institution | Tokyo Institute of Technology |
|---|
Principal Investigator |
VACHA Martin 東京工業大学, 物質理工学院, 教授 (50361746)
|
|---|
| Project Period (FY) |
2014-04-01 – 2019-03-31
|
| Keywords | conjugated polymers / photophysics / single-molecule studies |
|---|
| Outline of Annual Research Achievements |
In the past year, research continued on the prototypical polyfluorene derivative PFO. Single chains of PFO were dispersed at minute concentrations in solid thin film matrices of polystyrene (PS) and poly(methyl methacrylate) (PMMA), as well as in solutions of cyclohexane, toluene or PS/toluene to simulate good and poor solvent environments and environments with different permeability and diffusion of oxygen, to systematically study the effects of intra-chain aggregation as well as oxidation on the appearance and characteristics of the green band. The effects of aggregation were further confirmed directly by measuring conformation of individual chains spin-coated from different solvents by high-resolution atomic force microscope. The single-molecule results reveal two fluorescence spectral forms in the region of the green emission, a vibrationally-resolved type located around 500 nm, and broad structureless type located between 520 and 575 nm, none of them sensitive to the presence of oxygen. These two types are characterized by different lifetimes of 1.4 ns and 5.1 ns, respectively, and their oscillator strengths are two orders of magnitude smaller compared to the blue emission band. These results point to two different optical transitions comprising the green band, and these have been assigned to the emission of H-aggregates and charge-transfer or indirectly excited excimer states, respectively.
|
| Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
The study of the single-chain conformation of conjugated polymers and its effect on photophysical properties, as well as its dynamics proceeded mainly according to the research plan. Single chains of PFO were studied dispersed in different polymer matrices representing good or poor solvents, in concentrated polymer solutions, or adsorbed on substrates and exposed to different solvents. These experiments were complemented with ensemble measurements of fluorescence lifetime and quantum yield, and with molecular dynamics calculations. The different types of aggregates were analyzed in terms of oscillator strength, which excluded the possibility of J-aggregation. Additional experiments using different excitation wavelengths helped to exclude directly excited excimer states as the origin of the green-band emission. The two types of green spectral band discovered were assigned to H-aggregates and charge-transfer complexes, respectively.
The second aspect of the study, the simultaneous measurement and control of the conformation by atomic force microscopy (afm) was hampered by a prolonged repair of an EM-CCD detector and will be continued.
|
| Strategy for Future Research Activity |
This year, the study of photophysical properties of conjugated polymers in relation to their conformation will continue. Effort will be concentrated on characterization of single chains or single nanoparticles of polyfluorene derivatives by simultaneous confocal and atomic force microscopy (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 an important feedback on the theoretical calculations of the various conformations of a polyfluorene chain and the corresponding emission spectra. For these studies, synthesis of thiol-capped polyfluorene derivatives is required, and work has begun on preparation for such synthesis. A next stage in the study by simultaneous confocal and afm microscopy on single chain or single nanoparticle will be electroluminescence using biased afm tip as an electrode, and feasibility of such will be also considered.
The collaborative work that started in the past years on novel photoresponsive conjugated molecules will continue by exploring derivatives of the molecule that have their absorption and emission spectral regions shifted towards lower energies, and at the same time show a ‘flapping’ motion when excited into the first singlet state, with a final goal of achieving reliable single-molecule methods towards nanoscale probing of local rigidity and dynamics of polymers and soft matter.
|
| Causes of Carryover |
単一分子蛍光イメージングおよび分光に欠かせないCCDカメラが故障し、修理が６ヶ月ほどかかったため、研究計画に遅れがでた。研究計画の１部を平成３０年度で行う。
|
