Fluorescent 2-(2′-hydroxybenzofuran)benzoxazole (HBBO) borate complexes: synthesis, optical properties, and theoretical calculations

The multi-step synthesis, structural and optical properties of original luminescent borate complexes derived from 2-(2 '-hydroxybenzofuran)benzoxazole (HBBO) are reported. Functionalization at position 3 of the benzofuran ring was readily achieved through an electrophilic cyclization key step followed by a Sonogashira cross-coupling reaction. The optical properties of the resulting boron difluoride dyes highlight different photophysical behaviors depending on the nature of the substitution at position 3 of the benzofuran core (Bu-t-phenylacetylene or (NBu2)-Bu-n-phenylacetylene). The (NBu2)-Bu-n-phenylacetylene moiety favors a sizeable intramolecular charge transfer as evidenced by a strong solvatochromism; a feature further confirmed by ab initio calculations. (C) 2014 Elsevier Ltd. All rights reserved.