Synthesis and Fluorescent Properties of Difluoroboron Dibenzoylmethane Polycaprolactone

Difluoroboron beta-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 dibenzoyl methane-poly lactide (BF(2)dbmPLA) 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 BF(2)dbmPCL (PCL = poly-(epsilon-caprolactone), a semicrystalline polymer) of different molecular weights ranging from similar to 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 temperatures (0 to -78 degrees C), however, and both intensities and lifetimes increase as the temperature is dropped. Polymer thermal properties were also examined. Aside from in the lowest molecular weight sample, the dye end group showed little effect on melting and glass transition temperatures. Theses dye-modified materials lend useful optical imaging capability to PCL, a polymer commonly used in drug delivery and tissue engineering applications.