Oxygen Sensing Difluoroboron Dinaphthoylmethane Polylactide

Abstract

Dual emissive luminescence 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 demonstrated differences <i>in vitro</i> ratiometric measurement of oxygen.