Rotational Energy Barrier of 2-(2′,6′-Dihydroxyphenyl)benzoxazole: A Case Study by NMR
作者:Weihua Chen、Eric B. Twum、Linlin Li、Brian D. Wright、Peter L. Rinaldi、Yi Pang
DOI:10.1021/jo201890f
日期:2012.1.6
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 center dot center dot center dot H-O (e.g., 1a) and N center dot center dot center dot H-O bonding (e.g., 1b), correlation of NMR with fluorescence data reveals that the rotamer with N center dot center dot center dot H-O bonding is predominant in the solution.