Synthesis and Fluorescent Properties of Difluoroboron Dibenzoylmethane Polycaprolactone

Abstract

Difluoroboron β-diketonate dyes are noted for their intense fluorescence, one- and two-photon absorption, solvatochromism, and good aqueous stability. Incorporation of these dyes into polymers leads to processable optical materials, which in some cases display additional emissive features. For example, previously we reported that difluoroboron dibenzoylmethane−polylactide (BF2dbmPLA) exhibits both fluorescence and room temperature phosphorescence (RTP). Typically RTP is ascribed to a matrix effect, where the rigid ordered medium restricts dye molecular motions, and excited-state decay via thermal pathways is hindered in favor of radiative decay. To test polymer effects on dye emissive properties, this study explores BF2dbmPCL (PCL = poly(e-caprolactone), a semicrystalline polymer) of different molecular weights ranging from ∼3 to 18 kDa. PCL materials exhibit the expected intense fluorescence and molecular weight dependent emission but, surprisingly, no RTP. Phosphorescence is evident at lower temperature...