Iridium(III) Bipyridine-Carbohydrate Complexes as Cellular Uptake Indicators

A series of luminescent cyclometalated iridium(III) bipyridine complexes appended with a carbohydrate unit [Ir(N^C)2(N^N)](PF6) (HN^C = 2-((1,1’-biphenyl)-4-yl)benzothiazole) (Hbt), 2-phenylpyridine (Hppy), 2-phenylquinoline (Hpq), 7,8-benzoquinoline (Hbzq), N^N = 4-(10-N-methyl-N-(b-D-glucopyranosyl)-amino-oxy-2,5,8-trioxa-decyl)-4’-methyl-2,2’-bipyridine (bpy-TEG-ONCH3-b-D-glc), 4-(10-N-methyl-N-(b-D-galactopyranosyl)-amino-oxy-2,5,8-trioxa-decyl)-4’-methyl-2,2’-bipyridine (bpy-TEG-ONCH3-b-D-gal)) has been synthesized, characterized, and their photophysical properties investigated. Upon photoexcitation, all the complexes exhibited green to yellow luminescence in fluid solutions at 298 K and in low-temperature glass, which originated from a triplet metal-to-ligand charge-transfer (3MLCT) (dp(Ir) ® p*(N^N) or triplet intraligand (3IL) (p ® p*) (N^N and N^C) emissive state. The lipophilicity and cytotoxicity of these complexes have been studied. Also, the cellular uptake efficiencies of one of the glucose complexes in the presence of different biological molecules such as glucose, insulin, and other chemicals have been examined. Furthermore, the intracellular distribution and photostability of this complex have been investigated by laser-scanning confocal microscopy.