Chasing Self-Assembly of Thioether-Substituted Flavylium Salts in Solution and Bulk State

Abstract

Two series of flavylium triflates carrying alkoxy side chains in the A-ring (benzo unit of chromylium salt) and thioethers in the B ring (phenyl unit) (O_n -Fla-S_m ) as well as thioethers at both A and B ring (S_n -Fla-S_m ) were synthesized in order to understand the effect of thioether functionalization on their self-assembly and electronic properties. Concentration-dependent and diffusion ordered (DOSY) NMR experiments of O₁ -iV-Fla-S₃ indicate the formation of columnar H-aggregates in solution with antiparallel intracolumnar stacking of the AC unit (chromylium) of the flavylium triflate, in agreement with the solid state structure of O₁ -V-Fla-S₁ . Thioether substitution on the B ring changes the linear optical properties in solution, whereas it has no effect on the A ring. According to differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction bulk self-assembly of these ionic liquid crystals (ILCs) depends on the total number of side chains, yielding SmA and Lam_Col phases for ILCs with 2-3 chains and Col_ro , Col_h phases for ILCs with 3-6 chains. Thus, we demonstrated that thioethers are a useful design tool for ILCs with tailored properties.

Keywords: DOSY; NMR methods; flavylium salts; ionic liquid crystals; liquid crystals.