Multichannel-Emissive V‑Shaped Boryl-BODIPY Dyads: Synthesis, Structure, and Remarkably Diverse Response toward Fluoride

Three
new V-shaped boryl-BODIPY dyads (1–3) were synthesized
and structurally characterized. Compounds 1–3 are
structurally close molecular siblings differing only in the number
of methyl substituents on the BODIPY moiety that were found to play
a major role in determining their photophysical behavior. The dyads
show rare forms of multiple-channel emission characteristics arising
from different extents of electronic energy transfer (EET) processes
between the two covalently linked fluorescent chromophores (borane
and BODIPY units). Insights into the origin and nature of their emission
behavior were gained from comparison with closely related model molecular
systems and related photophysical investigations. Because of the presence
of the Lewis acidic triarylborane moiety, the dyads function as highly
selective and sensitive fluoride sensors with vastly different response
behaviors. When fluoride binds to the tricoordinate borane center,
dyad 1 shows gradual quenching of its BODIPY-dominated
emission due to the ceasing of the (borane to BODIPY) EET process.
Dyad 2 shows a ratiometric fluorescence response for
fluoride ions. Dyad 3 forms fluoride-induced nanoaggregates
that result in fast and effective quenching of its fluorescence intensity
just for ∼0.3 ppm of analyte (i.e., 0.1 equiv ≡ 0.26
ppm of fluoride). The small structural alterations in these three
structurally close dyads (1–3) result in exceptionally
versatile and unique photophysical behaviors and remarkably diverse
responses toward a single analyte, i.e., fluoride ion.