A series of fluorescent dimeric imidazo[1,5‐a]pyridinium salts have been synthesized. These salts displayed large Stokes shifts (up to 196 nm), possessed good water solubility, and exhibited blue to yellow emission (Φem=up to 0.50) in solution. When one specific compound was used for co‐incubation of HeLa cells, green fluorescent signals were observed. The combined use of the salt and commercially available blue fluorescent dye realized the double staining of HeLa cells under the single UV excitation.

N,N′-Dimethylated imidazo[1,5-a]pyridinium salt having good water solubility and exhibiting fluorescence emission was found to work as not only a bioimaging agent but also a therapeutic agent under UVA-LED irradiation conditions. Because the continuous UVA-LED irradiation to HeLa cells stained by the synthesized salt resulted in the cell death due to the mitochondrial damage, the salt has a potential application as photodynamic therapy agent against tumor cells.

We designed and synthesized dimeric imidazo[1, 5-a]pyridines possessing various aryl groups at 1,1'-positions. The solution of these derivatives exhibited fluorescence emission in wavelength range of 487-512 nm. The fluorescence emissions were slightly red-shifted under acidic condition by addition of trifluoroacetic acid. Furthermore, the original fluorescence spectra were observed after the addition of triethylamine as a base.[a] Prof.

We designed a new class of N‐type ligands bearing an imidazo[1,5‐a]pyridine moiety and synthesized seven imidazo[1,5‐a]pyridine derivatives. The palladium‐catalyzed Mizoroki–Heck reaction of aryl bromides and chlorides with alkenes using our imidazo[1,5‐a]pyridine‐PdCl2 system afforded the desired products in good‐to‐high yields with the low palladium loadings and short reaction times.

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