In:
Chemistry – A European Journal, Wiley, Vol. 22, No. 41 ( 2016-10-04), p. 14688-14695
Abstract:
A series of compounds containing 5‐(2‐aminobenzylidene)‐2,3‐dimethyl‐3,5‐dihydro‐4 H ‐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 〈 COCH 3 〈 COPh 〈 Tosyl 〈 COCF 3 . 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 %.
Type of Medium:
Online Resource
ISSN:
0947-6539
,
1521-3765
DOI:
10.1002/chem.201602425
Language:
English
Publisher:
Wiley
Publication Date:
2016
detail.hit.zdb_id:
1478547-X
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