posted on 2017-09-06, 19:12authored byMargaret L. Daly, Caroline Kerr, Christopher A. DeRosa, Cassandra L. Fraser
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.