Role of Boron in the Polymer Chemistry and Photophysical Properties of Difluoroboron−Dibenzoylmethane Polylactide

Abstract

Difluoroboron β-diketonate−polymer conjugates have remarkable solid-state luminescent properties that are useful in a variety of fields including multiphoton microscopy, cell biology, and tumor hypoxia imaging. Despite the successful applications of these systems, the role of boron in these polymeric materials has not been thoroughly investigated. Here we explore a boron-free model system with dibenzoylmethane chromophores in poly(lactic acid) (PLA) for comparison. The hydroxyl-functionalized aromatic diketone, dibenzoylmethane (dbmOH), is weakly fluorescent in the solid state and nonfluorescent in solution while its difluoroboron complex (BF2dbmOH) is highly emissive in both states. Using dbmOH and BF2dbmOH as initiators, well-defined end-functionalized polylactides, dbmPLA and BF2dbmPLA, were obtained via tin-catalyzed controlled ring-opening polymerization. Boronation of the dbmOH initiator affects the polymerization kinetics and the photophysical properties of the resulting BF2dbmPLA material. Both dbmPLA and BF2dbmPLA are dual emissive in the solid state, exhibiting both fluorescence and room-temperature phosphorescence (RTP), whereas only BF2dbmPLA is luminescent in solution. These results suggest that boron plays two roles: (1) as a protecting group in the polymerization and (2) as an emission enhancer. Finally, the presence of dual emission for both polymers indicates that it may be the diketone core structure rather than the difluoroboron that is essential for RTP in a rigid PLA matrix.

Meta‐Dimethoxy‐Substituted Difluoroboron Dibenzoylmethane Poly(Lactic Acid) Nanoparticles for Luminescence Anisotropy

“…Similar properties were observed for the initiator and P1 (Figure S1, Supporting Information). As expected, the side group and polymer MW did not significantly influence the optical properties in solution, consistent with previous reports …”

Oxygen Sensing Difluoroboron β-Diketonate Polylactide Materials with Tunable Dynamic Ranges for Wound Imaging

“…The more rapid attenuation in luminescence for these X-NP samples could also be due to lower initial dye loadings (i.e. dyePLA MWs) affecting BF 2 hydrolysis 41 or PLA degradation. And because phosphorescence is typically only present for BF 2 bdk dyes in ordered media (e.g.…”

Gas Response Behaviour and Photochemistry of Borondiketonate in Acrylic Polymer Matrices for Sensing Applications

“…At the concentration used in the preparation of the dye/monomer solution (~2.2 mmolal) no observation of aggregation has been reported [32]. Though aggregation of the dye after polymerization could lead to ground state interactions that have been suspected of changes in the excitation spectra [23]. The solubility of the dye was lower in the less polar matrixes (see Table 1), which could justify a stronger aggregation on the later compared to the more polar pTHFa and pDEGa.…”

“…By chemical modification, the dye can be grafted onto the backbone of the polymer chain, which improves dye stability and material homogeneity, by reducing aggregation or precipitation at high dye concentrations and by protecting from chemical degradation [21]. Whereas the dispersion of the DBMBF 2 dye in polymeric matrices, such as polymethylmethacrylate [22] or polylactic acid has been reported, analysis of the exciplex formation within such matrices is lacking [23]. The limited understanding of the exciplex formation in polymers matrices hampers further sensor development for MAH based on this class of materials.…”