Unsymmetrical 2,4,6‐Triarylpyridines as Versatile Scaffolds for Deep‐Blue and Dual‐Emission Fluorophores

Abstract

Pyridines substituted with different aromatic groups at C-2, C-4 and C-6 were prepared following a Kröhnke synthetic route. Introducing ortho-anisole at C-2 resulted in deep blue emitters in solution, with quantum yields up to 74 %. On the other hand, when ortho-phenol was introduced, forming a strong hydrogen bond with the pyridine nitrogen, excited-state intramolecular proton transfer was witnessed by the dual emission of the fluorophores, which is sensitive to the dye environment. The phenyl ring at C-4 was used to introduce electron-donating or withdrawing groups, to fine-tune the photophysical properties of the dyes. Crystal structures of the fluorophores, together with theoretical studies using DFT/TD-DFT calculations, were used to rationalize the experimental photophysical properties of the two families of dyes. Unsymmetrical 2,4,6-triarylpyridines are therefore versatile scaffolds for the preparation of deepblue and dual emission fluorophores, and are promising building blocks for luminescent devices and sensors.

Decoration of A-Ring of a Lupane-Type Triterpenoid with Different Oxygen and Nitrogen Heterocycles

“…Once again, using the methyl ( E )-2-(4-methoxybenzylidene)betulonate ( 3b ) as starting material, the reaction was performed in the presence of an excess of the Kröhnke salt 7 and ammonium acetate, in refluxing acetic acid for 24 h. Compound 8 was obtained in poor yield (25%), still recovering some starting material 3b . In the literature, for simpler triarylpyridine derivatives, prepared through a similar methodology, it was observed that the presence of strong electron-donating groups, such as dimethylamino or methoxy groups, did not favor the reaction, since the corresponding triarylpyridines were obtained in poor yields (24–37%) [ 28 ]. Therefore, this might have happened for the diarylpyridine-fused BoOMe compound 8 , as the starting material 3b also possesses a strong electron-donating methoxy substituent.…”

Benzimidazole-Based N,O Boron Complexes as Deep Blue Solid-State Fluorophores

“…All compounds are fluorescent in DMSO solution and show large Stokes’ shifts of ca. 125 nm, characteristic of fluorophores presenting ESIPT [ 43 , 45 , 46 ]. The maximum emission wavelength of 7b – d is also slightly red shifted (5–10 nm) moving down the halogen series ( Figure 3 ).…”

Excited‐State Proton Transfer in Luminescent Dyes: From Theoretical Insight to Experimental Evidence

“…In the example of Figure 8, the relative minimum of the excited state directly demonstrated the transfer of the proton from the phenol to the pyridine. [51] However, this is not always the case, due to inadequate calculation parameters or system definition. Alternatively, one can propose an excited-state geometry and vary the parameters such as bond length or angle torsion.…”