2004 Fiscal Year Final Research Report Summary
Fluorescence Thermochromism of Organic Crystals
| Project/Area Number |
14340193
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Organic chemistry
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| Research Institution | The University of Tokyo |
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Principal Investigator |
OGAWA Keiichiro The University of Tokyo, Graduate School of Arts and Sciences, Associate Professor, 大学院・総合文化研究科, 助教授 (50114426)
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| Co-Investigator(Kenkyū-buntansha) |
HARADA Jun The University of Tokyo, Graduate School of Arts and Sciences, Research Associate, 大学院・総合文化研究科, 助手 (00313172)
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| Project Period (FY) |
2002 – 2004
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| Keywords | Thermochromis / Tautomerization / Fluorescence quantum yield / Salicylideneanilines / Variable temperature diffuse refelectance spectra |
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| Research Abstract |
Reversible change in color of substances with variation of the temperature is known as thermochromism and has attracted much interest from chemists for a long time. In many cases the color deepens with raising of the temperature and pales with lowering of the temperature. The color change is usually associated with a change in absorption spectra in visible region. The thermochromism is, therefore, interpreted in terms of a temperature-dependent shift of an equilibrium between colored and colorless forms of molecules that compose the substances. The color of substances is, however, dominated not only by absorption but also by emission of visible light, when the substances are luminescent. If emission spectra change in visible region with variation of the temperature, a thermochromism would also occur even if absorption spectra do not change. Such a thermochromism, which is called fluorescence thermochromism, has been, however, hardly known for organic compounds.
We demonstrate here that the thermochromism of salicylideneaniline (1) and its congeners, which belong to a class of the most well-known thermochromic organic compounds, is the fluorescence thermochromism. Crystals of thermochromic salicylideneanilines have been reported to be usually red at room temperature and become yellow with lowering of the temperature. The thermochromism was ascribed to the shift of the tautomeric equilibrium between the OH and NH forms with variation of the temperature [equation (l)]. Based on the reexamination of electronic absorption spectra, fluorescence spectra, and perceived colors, we present here a new interpretation for the origin of the thermochromism : The thermochromism of salicylideneanilines is not caused by the shift of the tautomeric equilibrium between the OH and NH forms but is caused mainly by the change of the fluorescence in intensity with variation of the temperature.
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Research Products
(12 results)
