Oxygen-Sensing Difluoroboron Thienyl Phenyl β-Diketonate Polylactides

Difluoroboron β-diketonate-polylactides are versatile oxygen-sensing materials. These materials have both fluorescence (F) and oxygen-sensitive, room-temperature phosphorescence (RTP). The fluorescence, being insensitive to oxygen, can act as an internal standard to the changing phosphorescence, and ratiometric sensing of oxygen can be achieved with these simple, single-component materials. To expand the range of colors for this family of fluorophores, a series of thienyl-phenyl-substituted dyes were synthesized with initiator sites for the ring-opening polymerization of lactide. Heavy atoms (Br and I) were added to the dye to modulate the phosphorescence intensity. These halide-substituted thiophene dyes readily aggregated in the poly(lactic acid) (PLA) matrix, generating two fluorescence peaks in air, one for monomer emission and another for aggregate emission. When the dye was dilute in PLA, as a blend, the iodo-thienyl derivative showed impressive singlet-triplet splitting, with blue fluorescence (440 nm) and orange phosphorescence (585 nm), the largest gap recorded for a boron β-diketonate dye. Nanoparticles fabricated from a mixture of PLA and dye-PLA conjugated polymer benefited from the large singlet-triplet splitting to yield oxygen sensitivity at levels between 0 and 21 %, which can be utilized in biological oxygen-sensing applications.