The synthesis, structural, and photophysical properties of a new series of original dyes based on 2-(2'-hydroxybenzofuran)benzoxazole (HBBO) is reported. Upon photoexcitation, these dyes exhibit intense dual fluorescence with contribution from the enol (E*) and the keto (K*) emission, with K* being formed through excited-state intramolecular proton transfer (ESIPT). We show that the ratio of emission intensity E*/K* can be fine-tuned by judiciously decorating the molecular core with electron-donating or -attracting substituents. Push-pull dyes 9 and 10 functionalized by a strong donor (nNBu2 ) and a strong acceptor group (CF3 and CN, respectively) exhibit intense dual emission, particularly in apolar solvents such as cyclohexane in which the maximum wavelength of the two bands is the more strongly separated. Moreover, all dyes exhibit strong solid-state dual emission in a KBr matrix and polymer films with enhanced quantum yields reaching up to 54 %. A wise selection of substituents led to white emission both in solution and in the solid state. Finally, these experimental results were analyzed by time-dependent density functional theory (TD-DFT) calculations, which confirm that, on the one hand, only E* and K* emission are present (no rotamer) and, on the other hand, the relative free energies of the two tautomers in the excited state guide the ratio of the E*/K* emission intensities.

Amoebae pose a potential health risk as pathogenic agents i. e. in the central nervous system or the cornea, early diagnostics are important to implement rapid treatments and reduce impact on human health. Thus, development of selective fluorescent tags for Amoebae is an important issue. Analogues of Miltefosine, a drug effective against various strains of freeliving amoebae, have been synthesized. They are derivatives of the 11-aminoundecylphosphocholine. Via a peptide bond, a strong emitting BODIPY was embedded to the structure. This compound (1) was used to selectively stain for Acanthamoeba castellanii. In order to test the effect of the insertion of the amide function in the alkylbackbone of this modified Miltefosine, a model molecule (2) was prepared by replacing the dye by the anisidyl moiety. Anti-amoebic activity was evaluated for both.