A Photoactivatable Far-Red/Near-Infrared BODIPY To Monitor Cellular Dynamics in Vivo

A mechanism
to photoactivate far-red/near-infrared fluorescence
with infinite contrast and under mild visible illumination was designed
around the photophysical properties of borondipyrromethene (BODIPY)
dyes and the photochemical behavior of oxazine heterocycles. Specifically,
the photoinduced and irreversible cleavage of an oxazine ring with
a laser line at 405 nm extends the electronic conjugation of a BODIPY
chromophore over a 3H-indole auxochrome with a 2-(4-methoxyphenyl)­ethenyl
substituent in position 5. This structural transformation shifts bathochromically
the main absorption band of the BODIPY component to allow the selective
excitation of the photochemical product with a laser line of 633 nm
and produce fluorescence between 600 and 850 nm. This combination
of activation, excitation, and emission wavelengths permits the visualization
of the cellular blastoderm of developing Drosophila
melanogaster embryos with optimal contrast and essentially
no autofluorescence from the biological specimen. Furthermore, the
sequential acquisition of images, after the photoactivation event,
enables the tracking of individual cells within the embryos in real
time. Thus, our structural design and operating principles for the
photoactivation of far-red/near-infrared fluorescence can evolve into
invaluable probes to monitor cellular dynamics in vivo.