Substances that exhibit triboluminescence, the emission of light from crystals upon mechanical fracture, have potential use in sensors devices for monitoring wear and material failure. From the earliest report of triboluminescence in sucrose crystals by Francis Bacon in 1605, the relationship between solid-state packing features and the presence of triboluminescent behavior has been unclear. While most evidence suggests noncentrosymmetric packing is required for triboluluminescence, most materials studied to date have been discovered by accident, not designed to exhibit this behavior. In an effort to prepare solid-state materials with rational design features to exhibit triboluminescent ehavior, we utilized mechanochemical methods to synthesize Mn(BINAPO2)Br2 (BINAPO2 = 2,2’-bis(diphenylphosphoryl)-1,1’-binaphthyl). Axially chiral BINAPO2 was used both as racemic mixtures and as the single S enantiomer. Structures of two polymorphs of the racemic Mn(R,S-BINAPO2)Br2 were determined by X-ray crystallography. The polymorph that crystallized in the noncentrosymmetric space group Pn packed with Z’=1, whereas the polymorph that crystallized in P21/c packed with Z'=2, with one enantiomer each in the asymmetric unit. The single enantiomer Mn(S-BINAPO2)Br2 was also characterized by crystallography and packed in the noncentrosymmetric chiral space group P21. The solid-state photoluminescence spectra of the two polymorphs of the racemic Mn(R,S-BINAPO2)Br2 were markedly different, one with red-pink emission and the other with a green emission. The single enantiomer Mn(S-BINAPO2)Br2 solid-state emission was very similar to the one of the racemic polymorphs. Intra- and intermolecular structural features and photophysical features will be discussed in light of potential triboluminescent properties.

Mechanochemical synthesis of chiral and achiral diphosphine dioxide manganese(II) complexes: Polymorphs and solid-state photoluminescence

255th National Meeting (2018)

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