Naphtyl- and pyrenyl-flavylium dyads: Synthesis, DFT and optical properties

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

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.

Flavylium Salts: A Blooming Core for Bioinspired Ionic Liquid Crystals

Thermotropic ionic liquid crystals based on the flavylium scaffold have been synthesized and studied for their structure-properties relationship for the first time. The mesogens were probed by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD). Low numbers of alkoxy side chains resulted in smectic (SmA) and lamello-columnar (LamCol ) phases, whereas higher substituted flavylium salts showed Colro as well as ordered and disordered columnar (Colho , Colhd ) mesophases. Mesophase width ranged from 13 K to 220 K, giving access to room temperature liquid crystals. The optical properties of the synthesized compounds were probed towards absorption and emission properties. Strong absorption with maxima between 444 and 507 nm was observed, and some chromophores were highly emissive with quantum yields up to 99 %. Ultimately, mesogenic and dye properties were examined by temperature-dependent emissive experiments in the solid state.