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.
Intramolecular hydrogen bonds play an important role in the fluorescence of 2‐ortho‐aminophenyl pyridines, shifting the emission colour from deep blue to cold white. These multi‐emissive dynamic systems bearing excited‐state intramolecular proton transfer (ESIPT) moieties are susceptible to pH. The cover feature illustrates how DFT and td‐DFT calculations can elucidate why different levels of protonation lead to different emission colours. Photochemists are depicted as sailing through the waves of a spectrum. More information can be found in the Research Article by A. M. S. Silva, S. Guieu, and co‐workers (DOI: 10.1002/chem.202201844).
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