Tunable Solid-State Thermochromism: Alkyl Chain Length-Dependent Conformational Isomerization of Bianthrones

The introduction of linear alkoxy chains into bianthrone promoted the aggregation of the minor twisted conformer and made it compete with the major folded conformer in the solid-state. Rapid evaporation approach to the methoxy- and n-butoxy-substituted derivatives provided powder mixtures of folded and twisted conformers as metastable solids. Upon heating the powders, different lengths of alkyl chains converged to different conformers via solid-state isomerization reaction with an apparent color change. Monitoring by FT-IR spectroscopy and powder XRD ensured that these isomerization reactions involve only conformational isomerization without pyrolysis. In addition, single crystal X-ray structure analysis revealed that twisted conformers with longer alkyl chains are stabilized in the solid-state by the synergistic effect of their inter-chain hydrophobic interactions and pi-pi stacking interactions.

Automated summary

The introduction of linear alkoxy chains into bianthrone promotes the aggregation of minor twisted conformers and competes with major folded conformers in the solid-state. Heating powders of substituted derivatives leads to isomerization reactions and color changes, indicating the convergence of alkyl chains to different conformers. These reactions involve only conformational isomerization without pyrolysis, as confirmed by FT-IR spectroscopy and powder XRD. Crystal structure analysis shows that twisted conformers with longer alkyl chains are stabilized in the solid-state by hydrophobic interactions and pi-pi stacking interactions.