N−H-Type Excited-State Proton Transfer in Compounds Possessing a Seven-Membered-Ring Intramolecular Hydrogen Bond
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- 作者：Yi-An Chen ; Fan-Yi Meng ; Yen-Hao Hsu ; Cheng-Hsien Hung ; Chi-Lin Chen ; Kun-You Chung ; Wei-Feng Tang ; Prof. Dr. Wen-Yi Hung and Prof. Dr. Pi-Tai Chou
- 刊名：Chemistry - A European Journal
- 出版年：2016
- 出版时间：October 4, 2016
- 年：2016
- 卷：22
- 期：41
- 页码：14688-14695
- 全文大小：1645K
- ISSN：1521-3765
文摘
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 %.