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

Abstract

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

“…71 All other chemicals were reagent grade from Sigma Aldrich and were used without further purification. The compounds 1-(6-(2-((tetrahydro-2H-pyran-2-yl)oxy)ethoxy)naphthalen-2-yl)ethanone 33 and methyl 6-iodo-2-naphthoate 72 were prepared as previously described. Poly(lactic-acid) was synthesized from ethylene glycol as previously described 53 (M n (GPC/MALS) = 13 800 Da, PDI = 1.03).…”

“…33 Reagent loadings, reaction times, and monomer conversions are presented in Table 1. At the end of each polymerization, an aliquot was taken to determine monomer conversion by 1 H NMR spectroscopy.…”

“…25–27 Difluoroboron β-diketonates (BF 2 bdks) are particularly interesting because of their exceptional luminescent properties in both solution and solid states. The Stokes shifts are large enough so that the dyes do not completely self-quench when concentrated, and the medium, 28 molecular packing, 29–32 or dye design 33 can modulate the solid-state luminescence. The ligand framework also provides a versatile scaffold for functionalization by mesogens, 34 polymers, 35–37 heavy atoms, 38 or chelators.…”

“…63 Also, recently reported naphthyl-phenyl based BF 2 bdkPLA conjugates were synthesized with red-shifted dual-emissive optical properties. 33 …”

Recent progress of optical functional nanomaterials based on organoboron complexes with β-diketonate, ketoiminate and diiminate

“…Finally, these modified diketonates show the dual-emission property via fluorescence and phosphorescence. 13 Under aerobic conditions, only phosphorescence is quenched. By calculating the intensity ratio between the fluorescence and phosphorescence, and fitting with the standard line, the local oxygen level around the diketonate can be estimated.…”