title: N-H-Type Excited-State Proton Transfer in Compounds Possessing a Seven-Membered-Ring Intramolecular Hydrogen Bond.
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 %.
authors.affiliation: Department of Chemistry, Center for Emerging Material and Advanced Devices, National Taiwan University, Taipei, 10617, Taiwan R.O.C.
authors.forename: Yi-An
authors.initials: YA
authors.lastname: Chen
authors.affiliation: Department of Chemistry, Center for Emerging Material and Advanced Devices, National Taiwan University, Taipei, 10617, Taiwan R.O.C.
authors.forename: Fan-Yi
authors.identifier: http://orcid.org/0000-0003-1745-1636
authors.initials: FY
authors.lastname: Meng
authors.affiliation: Department of Chemistry, Center for Emerging Material and Advanced Devices, National Taiwan University, Taipei, 10617, Taiwan R.O.C.
authors.forename: Yen-Hao
authors.initials: YH
authors.lastname: Hsu
authors.affiliation: Department of Chemistry, Center for Emerging Material and Advanced Devices, National Taiwan University, Taipei, 10617, Taiwan R.O.C.
authors.forename: Cheng-Hsien
authors.initials: CH
authors.lastname: Hung
authors.affiliation: Department of Chemistry, Center for Emerging Material and Advanced Devices, National Taiwan University, Taipei, 10617, Taiwan R.O.C.
authors.forename: Chi-Lin
authors.initials: CL
authors.lastname: Chen
authors.affiliation: Department of Chemistry, Center for Emerging Material and Advanced Devices, National Taiwan University, Taipei, 10617, Taiwan R.O.C.
authors.forename: Kun-You
authors.initials: KY
authors.lastname: Chung
authors.affiliation: Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung, 20224, Taiwan R.O.C.
authors.forename: Wei-Feng
authors.initials: WF
authors.lastname: Tang
authors.affiliation: Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung, 20224, Taiwan R.O.C.
authors.forename: Wen-Yi
authors.initials: WY
authors.lastname: Hung
authors.affiliation: Department of Chemistry, Center for Emerging Material and Advanced Devices, National Taiwan University, Taipei, 10617, Taiwan R.O.C.. chop@ntu.edu.tw.
authors.forename: Pi-Tai
authors.initials: PT
authors.lastname: Chou
keywords: fluorescence; hydrogen bonds; kinetics; proton transfer; thermodynamics