| Abstract
| - Eight B-containing compounds, i.e., 1a−h, were prepared as mimics of the green fluorescentprotein (GFP) fluorophore. The underlying concept was that synthetic GFP chromophore analogues arenot fluorescent primarily because of free rotation about an aryl−alkene bond (Figure 1b). This rotation isnot possible in the β-barrel of GFP; hence, the molecule is strongly fluorescent. In compounds 1a−h,radiationless decay via this mechanism is prevented by complexation of the BF2 entity. The target materialswere prepared via two methods; most were obtained according to the novel route shown in Scheme 1b,but compound 1f was made via the procedure described in Scheme 2. Both syntheses involved formationof undesired compounds E-4a−h that formed simultaneously with the desired isomeric intermediates Z-4a−h. Both compounds form BF2 adducts, i.e., 1a−h and 5a−h, respectively. Methods used for spectroscopiccharacterization and differentiation of compounds in the series 1 and 5 are discussed, and these aresupported by single-crystal X-ray diffraction analyses for compounds 1c, 5c, 1f, and 5f. Electronic spectraof compounds 1a−h and 5a−h were studied in detail. Those in the 5 series were shown to be only weaklyfluorescent, but the 1 series were strongly fluorescent compounds (comparable to the boraindacene,BODIPY, dyes). Compounds 1g and 1h are water soluble, and 1h has particularly significant potential asa probe, since it also has a carboxylic acid group for attachment to biomolecules.
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