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).