Proximity effects on the phosphorescent properties of dinuclear salicylaldiminato cyclometalated iridium(III) complexes linked with polymethylene spacers

Abstract

The synthesis, structure and photophysical properties of dinuclear bis(phenylpyridine)(salicylaldiminato)Ir(III) complexes bearing polymethylene linkers are described herein. Chiral and achiral dinuclear Ir complexes bearing short (n = 2), medium (n = 5) and long (n = 8) polymethylene linkers were prepared by reacting [Ir(2-phenylpyridinato)IrCl]2 with the corresponding salicylaldimine derivatives. The facial configurations of the coordination sites and the polymethylene-linked structures were unequivocally established based on X-ray crystallography. The emission wavelengths of these polymethylene-linked binuclear complexes in 2-MeTHF in a glassy state at 77 K were found to vary with the length of the linker, such that a hypsochromic shift from yellow to green was observed upon changing from pentamethylene (n = 5) or octamethylene (n = 8) to ethylene (n = 2) linkages. X-ray crystallography and 1H nuclear magnetic resonance analysis combined with density functional theory calculations demonstrated that the present chromism arises from variations in the proximity and conformational rigidity between the two iridium cores, both of which are controlled by the length of the polymethylene linkage.