RESUMEN
Herein, a full investigation of the optical properties and first-principles calculations of a large series of original 2-(2'-hydroxybenzofuran)benzazole (HBBX) dyes is described. The electronic substitution on the π-conjugated core of the fluorophores and the nature of the heteroatom (O, S, N) was varied extensively to assess the necessary parameters to trigger a partial frustration of the excited-state intramolecular proton transfer (ESIPT) process, which results in the emission of both tautomers, that is, enol and keto (E* and K*). The optical properties, studied in solution and in the solid state, revealed the appearance of either an intense single K* or a dual E*/K* emission; a feature that is highly dependent on the electronic substitution (donating or accepting), the heteroelement, and the close environment. Subtle modifications of these parameters allowed the establishment of structure-property relationships that were successfully rationalized by first-principles calculations. In particular, the E*/K* emission intensity ratio was shown to be directly related to the free energies of the two emissive tautomers in the excited state.
RESUMEN
A first series of polyanils were synthesized by a simple condensation between either isomers of phenylenediamine derivatives or 1,3,5-benzenetriamine and 4-(diethylamino)salicylaldehyde, while a second series resulted from the condensation between 4,6-dihydroxyisophthalaldehyde or 2,5-dihydroxyterephthalaldehyde and differently substituted anilines. All these polyanils showed good chelating abilities toward trivalent boron fragments such as BF2 or BPh2 to yield the corresponding boranils. The optical properties of these novel fluorophores have been studied both in solution and in the solid-state and show emission wavelengths covering the entire visible spectrum and near-infrared (NIR), depending on molecular structure, substitution, and environment. While faintly fluorescent in solution in their molecular state, some polyanils show typical aggregation-induced emission (AIE) behavior upon addition of increasing amounts of water in THF solution, leading to a sizable enhancement of fluorescence intensity.
RESUMEN
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.
RESUMEN
The synthesis, structural, and optical properties of a series of luminescent N-alkylated 2-(2'-hydroxyphenyl)benzimidazole (HBI) or N-arylated 9,10-phenanthroimidazole (HPI) borate complexes are described. The optical properties of these complexes as well as their corresponding ligands were evaluated in solution and the solid state. Efficient emission in the blue-green region was obtained with quantum yields up to 91% in CH2Cl2 and 27% in the solid state. These emissions originate from excited state intramolecular proton transfer (ESIPT) for the ligands and from a singlet excited state for the borate complexes.
