Fluorine-substituted cyclometallated rhodium(iii) complexes with α-diimine ancillary ligands: synthesis, structure, and photophysical and DNA-binding properties

Abstract

A series of cationic [Rh(dfppz)₂(N^N)]⁺ complexes, incorporating cyclometallating 1-(2,4-difluorophenyl)-1H-pyrazolato and α-diimine ligands [2,2′-bipyridine, 1,10-phenanthroline and their derivatives], were synthesized as PF₆⁻ salts via cleavage of the μ-dichloro-bridged dimer [(dfppz)₂Rh-μ-Cl]₂ with the respective N^N ligands. The complexes were fully characterized by NMR spectroscopy, electrospray ionization mass spectrometry, and single-crystal X-ray diffraction. Time-dependent DFT (TDDFT) studies were performed to gain insight into their electronic structures. At 77 K in 1 : 1 MeOH/EtOH glass matrices, the complexes exhibit intense luminescence, whereas in MeCN at ambient temperature, they are weakly emissive or non-emissive. Their photophysical behavior was systematically compared with that of non-fluorinated [Rh(ppz)₂(N^N)]⁺ analogues to evaluate the impact of fluorination on the emission properties. Preliminary DNA-binding studies were also conducted using emission titrations.