Spectroscopic Studies of Phosphazene Polymers Containing Photoluminescent Metal Complexes

A series of small phosphazene ligands with pendant 6‐phenyl‐2,2′‐bipyridyl moieties, namely L 1 [N 3 P 3 (OPh) 5 (OPhbpyPh)], L 2 [N 3 P 3 (biph) 2 (OPhbpyPh) 2 ], L 3 [N 3 P 3 ( t Bubiph) 2 (OPhbpyPh) 2 ], L 4 [N 3 P 3 (biph) 2 (OPhbpyPh)Cl] and L 5 [N 3 P 3 (biph) 2 (OPhbpyPh)(OPh)] [OPhbpyPh = 4‐(4‐phenoxy)‐6‐phenyl‐2,2′‐bipyridine, OPh = phenoxy, biph = 2,2′‐oxybiphenyl and t Bubiph = 4,4′‐di‐ tert ‐butyl‐2,2′‐oxybiphenyl], have been used to synthesise the new cyclometallated palladium(II) and platinum(II) complexes [(L 1 ‐H)PdCl], [(L 1 ‐H)PtCl], [(L 1 ‐H)(PdCl) 2 ], [(L 3 ‐H)(PdCl) 2 ], [(L 4 ‐H)PtCl], [(L 5 ‐H)PtCl] and the rhenium(I) complex [L 5 Re(CO) 3 Cl]. Single‐crystal X‐ray diffraction analysis was performed on the free ligand L 2 and the palladium complexes [(L 1 ‐H)PdCl] and [(L 3 ‐H)(PdCl) 2 ]. In both Pd II complexes, the metal centre lies in a distorted square‐planar geometry with an “N 2 CCl” donor set confirming the cyclopalladation. The ligand pendant arms are involved in intermolecular stacking interactions with adjacent molecules. A polyphosphazene (L 6 ) with 4‐ tert ‐butylphenoxy (O t BuPh) and the potential donor OPhbpyPh as pendant groups was prepared and used to synthesise metallopolymers with Re I and Pt II . Spectroscopic and computational studies were conducted to compare the discrete complexes with the polymers with similar metal pendants as well as to model compounds in the literature. By using UV/Vis and resonance Raman spectroscopic techniques it was found that very few deviations from known metal chromophores exist for both the triphosphazene‐ and polyphosphazene‐based complexes. The transient resonance Raman spectra of the Pt II complexes revealed a ligand radical anion signature associated with the N 2 C unit.