EMISSION AND NMR SPECTROSCOPIC EVIDENCE TO FLUORESCEIN METHYL-ETHER METHYL-ESTER ENANTIOPIC ISOMERS

The synthesized methyl ether methyl ester of fluorescein is separated into enantiotopic isomers on a triacetylcellulose chromatography column. The same isomers are also detected on carbon-13 NMR spectra. The ratio of isomers is found to be 4:1. The emission of fluorescein is enhanced fourfold at -196 degrees C in respects to 24 degrees C. It is estimated that the through space pi - pi interactions between the plane of fused rings and the o-benzoylate carboxyl group at more stable isomer configurations are the cause of emission enhancements at low temperatures.