The optical properties of meta-alkoxy-substituted difluoroboron dibenzoylmethane dyes were investigated in solution and in the solid state. Meta-alkoxy substitution induced strong intramolecular charge transfer (ICT) from the oxygen-donating substituent to the halide and boron acceptors in the excited state, as compared to the π-π∗ transition that is observed with para-alkoxy substitution. The optical properties of para- and meta-substituted alkoxy boron dyes were evaluated by calculations, in dilute solution, and in solid-state films. When embedded in amorphous matrixes (e.g., PLA, PMMA, PS, cholesterol), all dyes showed fluorescence (F) and phosphorescence (P) emission. In this report, we show that meta-substitution resulted in enhanced solvatochromism and an increased phosphorescence-to-fluorescence ratio in solid-state films compared to analogous para-substituted samples. With enhanced phosphorescence intensity via the heavy-atom effect, iodo-substituted dyes were further studied in PLA-PEG nanoparticles. Oxygen calibrations revealed stronger phosphorescence and a greater oxygen-sensing range for the meta- versus para-alkoxy-substituted dyes, features that are important for oxygen-sensing materials design.
Bibliographical noteFunding Information:
We thank the National Institutes of Health (R01 CA167250) for support of this work. We gratefully acknowledge the UVA Center for Undergraduate Excellence for Harrison Undergraduate Research Awards to M.L.D. and C.K. and the Beckman Scholars Program for a fellowship to C.K. We thank Dr. Tristan Butler and Dr. James N. Demas for helpful discussions.
- difluoroboron β-diketonate complexes
- oxygen sensing
- poly(lactic acid)
- room-temperature phosphorescence