Synthesis and Optical Properties of Red and Deep-Red Emissive Polymeric and Copolymeric BODIPY Dyes

Deep-red emissive polymeric BODIPY dyes (polymers A and B), poly(2,6-BODIPY-ethynylene)s, were prepared by palladium-catalyzed Sonogashira polymerization of 2,6-diiodo-functionalized BODIPY monomers with 2,6-diethynyl-functionalized BODIPY monomers. Poly(2,6-BODIPY-ethynylene)s emit in the deep-red region with emission spectral maxima at around 680 nm and exhibit significant red shifts (up to 163 and 172 nm) of both absorption and emission maxima compared with their initial BODIPY dyes due to significant extension of pi-conjugation. Red emissive copolymeric BODIPY dyes (polymers C, D, and E) were also prepared by palladium-catalyzed Sonogashira polymerization of a diethynyl-functionalized BODIPY monomer with 9,9-bis(6'-(hexylthio)hexyl)-2,7-diiodo-9H-fluorene, 1,4-diiodo2,5-didecyloxybenzene, and 2,5-diiodo-3-decylthiophene, respectively. Incorporation of different band gap monomer units into poly(2,6-BODIPY-ethynylene)s resulted in copolymers with a range of emission wavelengths from 641 to 664 nm. The fluorescence lifetimes of these polymers (polymers A-D) are from 2.8 to 3.8 ns except the copolymer with thiophene moieties (polymer E), which displays a much shorter lifetime of 0.23 ns with low fluorescence quantum yield due to efficient intersystem crossing induced by the heavy atom effect of sulfur.