Controlling Photophysical Properties of Systems Containing Multiple BODIPY Units Linked by Methylene Bridge

A series of tunable
multicolor emitting AIEgens (B1–B8) with multiple
BODIPY units linked by methylene and triazole bridges
have been synthesized and thoroughly characterized. Close proximity
of two symmetrical phenyl-BODIPY units in these systems enables them
to display dual-emission band [λmax, ∼530
and ∼560 nm] due to monomer and excimer emission. These bands
are sensitive to surroundings (concentration/temperature/solvent polarity)
and can transform into single color emission (i.e., green to yellow
and vice versa in solution while red in solid-state/dense medium).
Triple-color (green, yellow, and red) emission for these derivatives
can be achieved simply by changing concentration/viscosity of the
mediums or by aggregation. Triple-color tunability has been achieved
in solid poly­(methyl methacrylate) films as well. Crystal structure
analyses revealed nonplanar orientation with BODIPY units in close
proximity. This arrangement ensures J-aggregation responsible for
red emission in aggregated-/solid-state. Aggregation studies in DMSO/water
mixture illustrated excellent aggregation-induced emission with large
Stokes shift (up to 203 nm).