The Rational Development of Brighter, More Light-Stable Fluorescent Probes
James Foley
Senior Rowland Fellow
Rowland Institute at Harvard University
Abstract
Dyes that both fluoresce with high efficiencies and are stable to light-mediated
photodegradation are in great demand by many modern pure and applied luminescencebased technologies. One of the goals of our research group is to discover these kinds of
materials. We have recently developed a new type of a highly fluorescent rhodamine dye
that uses 7-azabicylco[2.2.1]heptyl moieties as the electron donating auxochrome groups.
Using the prototypical dye tetramethylsulforhodamine as a benchmark, we have found
this new dye has significantly higher fluorescent quantum yields,  emission
efficiencies that are invariant in the 20 -> 60 oC temperature range, and fluorescent
lifetimes that increase with a rise in temperature (20 -> 60 oC) as compared to a decrease
for the benchmark dye. Importantly, photostability studies found the azabicyclic
rhodamine to be many times more stable than its tetramethyl analogue. To the best our
knowledge this is the first time that an apex-N-substituted azabicyloalkane has been used
as an electron donor group in any class of donor-acceptor dye. Thus, the concept of using
an apex-substitutes bicyclic amine as a donor moiety constitutes a new paradigm for
simultaneously inducing remarkable beneficial effects on both emission efficiency and
photostability in a donor-acceptor fluorophore.