Filling the gap with a bulky diaryl boron group: fluorinated and non-fluorinated copper pyrazolates fitted with a dimesityl boron moiety on the backbone.

Successful synthesis has been reported of 4-MesB-3,5-(CF)PzH and 4-MesB-3,5-(CF)PzH bearing sterically demanding diarylboron moieties at the pyrazole ring 4-position, and their corresponding copper(I) pyrazolate complexes. They show visible blue photoluminescence in solution. The X-ray crystal structures revealed that the fluorinated {[4-BMes-3,5-(CF)Pz]Cu} crystallizes as discrete trinuclear molecules whereas as the non-fluorinated {[4-BMes-3,5-(CH)Pz]Cu} forms dimers of trimers with two close inter-trimer Cu⋯Cu separations. The solid {[4-BMes-3,5-(CF)Pz]Cu} featuring a sterically confined CuN core displays bright blue phosphorescence while {[4-BMes-3,5-(CH)Pz]Cu}, which is a dimer of a trimer, is a red phosphor at room temperature. This work illustrates the modulation of photo-physical properties of metal pyrazolates by adjusting the supporting ligand steric features and introducing secondary diarylboron luminophores. Computational analysis of the structures and photophysical properties of copper complexes are also presented.