The Anthracen-9-ylmethyloxy unit: an underperforming motif within the fluorescent PET (photoinduced electron...

Compound, which was designed to act as a fluorescent sensor for calcium according to the PET (Photoinduced Electron Transfer) principle, shows a relatively small Ca2+-induced fluorescence enhancement factor (FE) of 1.8 whereas its close relative is known to display a far higher FE value of 16. Though designed as fluorescent PET sensors for solvent polarity, compounds and also show negligible fluorescence enhancement as their environments are made progressively less polar even though their relatives and show limiting FE values of 53 and 3, respectively. Indeed, and are useful since they are fluorescent sensors for solvent polarity without being affected by Bronsted acidity. The poor sensory performance of and relative to their cousins is attributed to the presence of an oxygen proximal to the 9-position of an anthracene unit, which opens up a CT (charge transfer) channel. Normal PET sensing service is resumed when the offending oxygen is deleted.