2016 Fiscal Year Annual Research Report
| Project/Area Number |
15J02752
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| Research Institution | Tohoku University |
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Principal Investigator |
穆 帥 東北大学, 理学研究科, 特別研究員(DC1)
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| Project Period (FY) |
2015-04-24 – 2018-03-31
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| Keywords | ASE / ESIPT / π-π stacking |
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| Outline of Annual Research Achievements |
We developed a novel excited state intramolecular proton transfer (ESIPT)-active molecule (DSBTBT) based on benzothieno[3,2-b][1]benzothiophene. The platelet crystal were prepared by the physical vapor transport (PVT) method. Brighter luminescence on the edge than the body could be observed, which indicates good optical waveguide property of DSBTBT crystal.These observations suggest photons highly confined inside the crystal.
DSBTBT crystal exhibits highly efficient face to face π-π stacking and moderate photoluminescence (PL) quantum yield, which are thought to be the negative factors of the light amplification. PL spectrum of DSBTBT crystal exhibits only one intense emission band around 576 nm. However, a novel emission band around 554 nm appeared upon the pulsed laser excitation. This phenomenon highly suggests two emission bands come from two different Keto excited states. Interestingly, only emission band around 554 nm exhibits amplified spontaneous emission with a low threshold of 34 μJ/cm-2.These results suggest the promising potential of DSBTBT crystal as gain media for the organic laser.
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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
Development of gain media for solid state laser is a hot topic in the past decades. Organic molecular crystals, as novel gain media, exhibits promising application value for the optically or electrically pumped laser. However, studies found that the light amplification in the molecular packing with strong π-π stacking is normally forbidden. Thus, to explore the strategy of overcoming the suppression of π-π stacking towards the light amplification is important.
In our work, we developed a novel ESIPT-active molecular crystal based on benzothieno[3,2-b][1]benzothiophene building block. Due to the introduction of intramolecular hydrogen bonding sites,DSBTBT crystal is highly in favour of population inversion in the keto form. DSBTBT exhibits two emission bands, which highly suggests there are two keto excited states accompanied with molecular geometry change. Interestingly, only one emission band exhibits amplified spontaneous emission. Thus, the strategy of ESIPT as a key to overcome the suppression of highly efficient π-π stacking towards achieving low-threshold light amplification was proposed for the first time.
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| Strategy for Future Research Activity |
In our future work, we will further investigate the mechanism of light amplification from DSBTBT crystal. More optical and structure analysis will be conducted. Based on these, we will try to develop more laser gain media based on ESIPT-active molecules.
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