| Research Abstract |
Organic fluorescent pigment has been attracting considerable interest because of its potential application in variety of fields. In this project, we focused on developing new organic fluorescent pigment that has the 2,2'-bipyridine structure with unsymmetrical substituent(s). Preliminary results revealed that 6,6'-diamino-2,2'-bipyridine(dabp) showed strong fluorescence. A series of amino and chloro substituted bipyridines was synthesized, and it was found that 6-amino substituent was essential for strong blue fluorescence in solution and in solid. Among them, unsymmetrically substituted 6-amino-6'-chloro-2,2'-bipyridine(acbp) showed strongest emission (phi=0.8) with large Stokes shift(ca 90 nm), and weak electroluminescence was observed when dabp and acbp were fabricated in three layr-type EL device.
As acbp that has electron-donating and electron-withdrawing substituents on each pyridine unit showed strongest fluorescence with a large Stokes shift, possible role of intramolecular charge transfer between the two pyridine units at excited state was suggested. On the basis of these results, new aromatic amide-type host molecule that showed a twisted intramolecular charge transfer(TICT) emission with a large Stokes shift was synthesized, and it was shown that molecular recognition of the uracil derivatives with triple hydrogen bonding was directly monitored by modulation of the TICT emission.
Weak emission of dabp observed in protonic solvent at longer wavelength side was ascribed to the imide tautomer. Based on this observation, alkyl derivatives of dabp were synthesized, and the derivative demonstrated the ability to recognize fatty acids by multiple hydrogen bonding interaction and to monitor the interaction by alteration of its emission due to the amide-imide tautomerization.
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