Influence of Central Metal and Halide Size on the Structure and Photophysics of Group 4 Arylalkynyl Metallocenes and their CuX (X = Cl, Br, I) Complexes

Abstract

The structural and photophysical consequences of varying the central metal in a series of group 4 arylalkynyl metallocene complexes and varying the halide (X) in a series of heterobimetallic arylalkynyl metallocene complexes with CuX (X = Cl, Br, I) bound between the alkynes are investigated. We report the synthesis and characterization of bis-(xylylethynyl)-bis(pentamethylcyclopentadienyl)zirconium(IV), xyl [Cp*Zr] . X-ray crystallographic analysis reveals that this Zr complex is isostructural with its Ti analog, xyl [Cp*Ti] . The Zr complex exhibits a significant blue-shift in emission at 77 K, consistent with the more negative reduction potential of Zr IV . For the heterobimetallic complex series, xyl [Cp*Ti]CuX , increasing the halide size from Cl − to I − results in only subtle structural changes. Photophysical studies reveal that all CuX complexes are emissive in room-temperature fluid solution; however, the photoluminescence quantum yield decreases as the halide size increases (Cl > Br > I). This result opposed our initial hypothesis that increased halide size would increase steric congestion and lead to increased photoluminescence. We discuss possible reasons for the observed trend. These results continue to provide insights into the design of photosensitizers using earth-abundant d 0 transition metal complexes. An arylalkynyltitanocene with CuBr bound between the alkynes has recently been shown to act as a photosensitizer. Here we investigate the structural and photophysical impact of replacing Ti with Zr, and of replacing CuBr with either CuCl or CuI.