Development of tris-cyclometalated iridium complexes for cellular imaging through structural modification

Herein we report the synthesis and investigation of two novel Iris-cyclometalated iridium complexes derived from [Ir(ppy)(3)] and bearing an aminoalkyl substituent on one of the 2-phenylpyridine ligands. These complexes differ in the number of the alkyl substituents of the aminoalkyl group. Specifically, the complexes reported herein contain one (1) and two (2) 2-hydroxy ethyl groups on the nitrogen atom. Both complexes retain the good photophysical properties reported for earlier versions of this group of Iris-cyclometalated iridium complexes. However, the differences in the substitution result in changes in the responsive photoluminescence behavior in aqueous solutions. Live cell microscopy experiments revealed that the complexes can localize in NIH-3T3 cells. Finally, it has been observed that the complex containing two 2-hydroxy ethyl groups is less cytotoxic than the its mono-substituted counterpart.