Rotational Energy Barrier of 2-(2′,6′-Dihydroxyphenyl)benzoxazole: A Case Study by NMR

2-(2′-Hydroxyphenyl)­benzoxazole (HBO) derivatives represent an important class of luminescent materials, as they can undergo excited state intramolecular proton transfer (ESIPT). The material’s ESIPT properties are dependent on the ratio of two different rotamers, whose interconversion is poorly un...

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Bibliographic Details
Published in:Journal of organic chemistry 2012-01, Vol.77 (1), p.285-290
Main Authors: Chen, Weihua, Twum, Eric B, Li, Linlin, Wright, Brian D, Rinaldi, Peter L, Pang, Yi
Format: Article
Language:English
Subjects:
Chemistry
Exact sciences and technology
Heterocyclic compounds
Heterocyclic compounds with n hetero atom and also o and/or s, se, te hetero atoms
Organic chemistry
Preparations and properties
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Summary:2-(2′-Hydroxyphenyl)­benzoxazole (HBO) derivatives represent an important class of luminescent materials, as they can undergo excited state intramolecular proton transfer (ESIPT). The material’s ESIPT properties are dependent on the ratio of two different rotamers, whose interconversion is poorly understood. By using HBO derivative 4, the rotational energy barrier of 2- (2′,6′-hydroxyphenyl)­benzoxazole is determined to be 10.5 kcal/mol by variable-temperature NMR. Although a HBO derivative typically exhibits two rotamers with O···H–O (e.g., 1a) and N···H–O bonding (e.g., 1b), correlation of NMR with fluorescence data reveals that the rotamer with N···H–O bonding is predominant in the solution.
ISSN:0022-3263
1520-6904
DOI:10.1021/jo201890f