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|Title: ||N-H-Type Excited-State Proton Transfer in Compounds Possessing a Seven-Membered-Ring Intramolecular Hydrogen Bond|
|Authors: ||Pi-Tai Chou|
|Issue Date: ||2017-02-14T01:42:07Z
|Abstract: ||Abstract: A series of compounds containing 5-(2-aminobenzylidene)-2,3-dimethyl-3,5-dihydro-4H-imidazol-4-one (o-ABDI) as the core chromophore with a seven-membered-ring N−H-type intramolecular hydrogen bond have been synthesized and characterized. The acidity of the N−H proton and thus the hydrogen-bond strength can be fine-tuned by replacing one of the amino hydrogen atoms by a substituent R, the acidity increasing with increasing electron-withdrawing strength of R, that is, in the order H<COCH3<COPh<Tosyl<COCF3. The tosyl and trifluoroacetyl derivatives undergo ultrafast, irreversible excited-state intramolecular proton transfer (ESIPT) that results in proton-transfer emission solely in the red region. Reversible ESIPT, and hence dual emission, involving the normal and proton-transfer tautomers was resolved for the acetyl- and benzyl-substituted counterparts. For o-ABDI, which has the weakest acidity, ESIPT is prohibited due to its highly endergonic reaction. The results clearly demonstrate the harnessing of ESIPT by modifying the proton acidity and hydrogen-bonding strength in a seven-membered-ring intramolecular hydrogen-bonding system. For all the compounds studied, the emission quantum yields are weak (ca. 10−3) in dichloromethane, but strong in the solid form, ranging from 3.2 to 47.4 %.|
|Appears in Collections:||[光電科學研究所] 期刊論文|
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