Synthesis and tunable chiroptical properties of chiral BODIPY-based D-π-A conjugated polymers

Three novel donor-pi-acceptor (D-pi-A) type chiral polymers P1, P2, and P3 could be synthesized from diiodo-substituted chiral boron-dipyrromethene (BODIPY) derivative (M-1) with 2,7-diethynyl-9,9-dioctyl-9H-fluorene (M-2), 3,6-diethynyl-9-octyl-9H-carbazole (M-3), and 3,7-diethynyl-10-dodecyl-10H-phenothiazine (M-4) via a Pd-catalyzed Sonogashira coupling reaction, respectively. From the choice of the three different donor structures, the three chiral BODIPY-based conjugated polymers can exhibit a red fluorescent emission centered at around 624-650 nm, with tunable band gaps in the range 1.56-1.96 eV, respectively. Interestingly, compared with the anisotropy (r = 0.005) and the CPL dissymmetry factor (g(lum) < 0.01) of the chiral BODIPY small molecule as the counterpart, the three chiral polymers can exhibit a high r (up to 0.10 for P1) and a large glum (up to 0.32 for P2), which can be attributed to the interchain pi-pi stacking effect and the well-defined chiral arrangement along these polymers backbone.