Fluorine-Substituted Cyclometallated Rhodium(III) Complexes with α-Diimine Ancillary Ligands: Synthesis, Structure, 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 PF 6 - salts via cleavage of the μ-dichloro-bridged dimer [(dfppz) 2 Rh-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) study 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 nonemissive. 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.