Difluoroboron �-diketonate (BF2bdk) dyes are known for their unique mechanochromic luminescent (ML) properties. This typically manifests itself as a red-shift in the emission from the thermally annealed solid-state dye upon mechanical perturbation, followed by spontaneous recovery to the original state at room temperature. In essence, these materials are renewable inks. Treated surfaces can be inscribed, self-erase and inscribed again. We have studied the effects of various arenes, halides and alkyl substituents on ML emission color shift and room temperature self-erasing properties of this family of dyes. However, the effect on ML of substitution at the alpha carbon of the �-diketonate ligand has yet to be rigorously investigated. We hypothesize that such substitution will disrupt the formation of face-to-face H-aggregates of the molecules, which has been proposed to be the cause of ML and red-shifted emission upon smearing. Steric hindrance at the alpha position may diminish or completely eliminate ML, or result in faster recovery of the annealed emission after smearing. To test this hypothesis, a dibenzoylethane derivative, BF2dbe(OMe)2 where dbe = dibenzoylmethane with a methyl group in the alpha position, was synthesized. It exhibits bright blue emission in the solid state as isolated. However, the compound is practically non-emissive in solution (f?F? = 0.1% in CH2Cl2 solution). This is good evidence that the compound exhibits aggregation-induced emission (AIE). It also shows significantly less dramatic ML when compared to the difluoroboron dibenzoylmethane derivative BF2dbm(OMe)2. This shows that the methyl group at the alpha position of the �-diketonate core does, in fact, hinder ML. Findings with this and other alpha substituted analogues along with computational studies to better understand optimal confirmations, transitions, and molecular interactions will be presented.

Effects of alpha substitution on difluoroboron dibenzoylmethane mechanochromic luminescence<sub>
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247th National Meeting (2014)

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