Aromatic difluoroboron β-diketonate complexes (BF2bdks) are classic fluorescent molecules that have been explored as photochemical reagents, two-photon dyes, and oxygen sensors. To gain a better understanding of their emissive properties in both solution and polymer matrices, BF2bdks with varying aromatic groups were synthesized and their photophysical properties were investigated in both methylene chloride and poly(lactic acid) (PLA). Absorption spectra showed systematic variations that are well correlated with structural features, including the size of the aryl substituent and the presence of a para electron donating methoxy substituent. Computational modeling of the absorption spectra with the TD-B3LYP/6-311+G(d)//B3LYP/6-31G(d) formulation of density functional theory and a polarizable continuum model of dichloromethane solvent shows that all systems show intense π–π* one-electron excitations, usually from one of the highest occupied MOs (HOMO-k, k=0, 1, 2) to the lowest unoccupied MO (LUMO). Emission properties are sensitive to the dye structure and medium. Based on spectroscopic and lifetime studies, BF2bdks exhibit comparable fluorescence properties in both solutions and polymers when the diketonate group is functionalized with smaller aromatic ring systems such as benzene. For BF2bdks with larger arene ring systems, such as anthracene, emission from a strong intramolecular charge-transfer (ICT) state was also noted in both solution and in PLA. There are differences in relative intensities of peaks arising from π-π* and ICT excitations depending upon dye loading in PLA. Substituent effects were also observed. Electron-donating methoxyl groups on the aromatic rings lead to enhanced fluorescence quantum yields. For certain dyes, phosphorescence is detected at low temperature or under a nitrogen atmosphere in PLA matrices.

Many difluoroboron b-diketonate (BF 2 bdk) compounds display mechanochromic luminescence (ML) and substituents can influence their optical properties. For example, the difluoroboron iododibenzoylmethane derivative, BF 2 dbm(I)OC 12 H 25 , exhibits mechanochromic luminescence quenching (MLQ). When annealed films of this dye are smeared under air, the perturbed region becomes dim under UV light. In this study, effects of differing halide substituents on ML were investigated. A series of dyes of the form BF 2 dbm(X)OC 12 H 25 , where X ¼ H, F, Cl, Br, and I, were synthesized. The luminescence properties of these dyes were studied in CH 2 Cl 2 solution, as films on weighing paper, spin-cast films on glass substrates, and as bulk powders. All of the dyes exhibit ML and MLQ. Solid-state emissions from these dyes are also sensitive to annealing temperature. The F, Cl, and Br dyes required higher annealing temperatures than the H and I analogues to achieve ordered emissive states. Spin-cast films of the dyes on glass were studied using atomic force microscopy (AFM) and X-ray diffraction (XRD), revealing a change from an amorphous material in the as-spun state to an ordered, crystalline material after annealing, with the F and Cl dyes showing a propensity to form large lamellar crystallites. Powders were also investigated using XRD and showed changes in diffraction patterns corresponding to thermal annealing and grinding. Finally, halogen substituents greatly diminished the ability of the dye films to recover their ordered emissive states after smearing under ambient conditions. These dyes could be useful for applications in which a more permanent inscription is desirable.