Ruthenium Complexes Bearing Axially Chiral Bipyridyls: The Mismatched Diastereomer Showed Red Circularly Polarized Phosphorescence

Ruthenium(II) complexes bearing three axially chiral bipyridyl ligands were synthesized as a new family of chiral complex dyes, and Delta-(S)- and ?-(S)-diastereomers were obtained. The X-ray crystal structure analyses, spectroscopy, and DFT calculations suggested that all the bipyridyls maintained chirality in both the ground and excited states, and the Delta-(S)- and ?-(S)-isomers are the matched (more relaxed) and mismatched (more constrained) pairs, respectively. The mismatched ?-(S)-isomer exhibited red circularly polarized phosphorescence (CPP) both in solution and in the solid state. The solution state CPP is the most intense of ruthenium complexes, while the solid state CPP is the first example of them. It is supposed that, for the ?-(S)-isomer, the six cumulative CH/pi interactions suppress further distortion in the T-1 state.

Automated summary

A new family of chiral complex dyes was synthesized with ruthenium(II) complexes bearing three axially chiral bipyridyl ligands. The Delta-(S)- and ?-(S)-diastereomers exhibited different circularly polarized phosphorescence properties, with the ?-(S)-isomer showing significant CH/pi interactions to suppress distortion in the excited state T-1.