Dual-Emissive Difluoroboron Naphthyl-Phenyl β‑Diketonate Polylactide Materials: Effects of Heavy Atom Placement and Polymer Molecular Weight

Luminescent materials are important for imaging and sensing. Aromatic difluoroboron β-diketonate complexes (BF₂bdks) are classic fluorescent molecules that have been explored as photochemical reagents, two-photon dyes, and oxygen sensors. A series of BF₂bdks with naphthyl and phenyl groups was synthesized, and photophysical properties were investigated in both methylene chloride and poly­(lactic acid) (PLA). Polymer molecular weight and dye attachment site along with bromide heavy atom placement were varied to tune optical properties of dye–PLA materials. Systems without heavy atoms have long phosphorescence lifetimes, which is useful for lifetime-based oxygen sensing. Bromine substitution on the naphthyl ring resulted in intense, clearly distinguishable fluorescence and phosphorescence peaks important for ratiometric oxygen sensing and imaging

Oxygen Sensing Difluoroboron Dinaphthoylmethane Polylactide

Dual emissive properties of solid-state difluoroboron β-diketonate-poly­(lactic acid) (BF₂bdk-PLA) materials have been utilized as biological oxygen sensors. Dyes with red-shifted absorption and emission are important for multiplexing and <i>in vivo</i> imaging, thus hydroxyl-functionalized dinaphthoylmethane initiators and dye-PLA conjugates BF₂dnm­(X)­PLA (X = H, Br, I) with extended conjugation were synthesized. The luminescent materials show red-shifted absorbance (∼435 nm) and fluorescence tunability by molecular weight. Fluorescence colors range from yellow (∼530 nm) in 10–12 kDa polymers to green (∼490 nm) in 20–30 kDa polymers. Room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) are present under a nitrogen atmosphere. For the iodine-substituted derivative, BF₂dnm­(I)­PLA, clearly distinguishable fluorescence (green) and phosphorescence (orange) peaks are present, making it ideal for ratiometric oxygen-sensing and imaging. Bromide and hydrogen analogues with weaker relative phosphorescence intensities and longer phosphorescence lifetimes can be used as highly sensitive, concentration independent, lifetime-based oxygen sensors or for gated emission detection. BF₂dnm­(I)­PLA nanoparticles were taken up by T41 mouse mammary cells and successfully detected differences in oxygen levels during <i>in vitro</i> ratiometric imaging