Fluorescence and Chiroptical Properties of Cyclic Aromatic Triamides with Isolated and Extended Conjugated Systems

Chiroptical properties of cyclic aromatic triamides with isolated and extended conjugated systems are studied to develop promising circularly polarized luminescence (CPL) materials. Cyclic aromatic triamides containing 1,4-bis(phenylethynyl)benzene units exhibited dual fluorescence emission, while single and bright fluorescences are observed for those substituted with naphthalene ring. CPL emissions are observed for the compounds bearing three conjugated systems.

This study synthesizes cyclic and acyclic aromatic triamides with conjugated systems to establish molecular design guidelines for obtaining reliable circularly polarized luminescence (CPL)-active materials. For the compounds with the phenylacetylene unit, the acyclic derivative shows a single fluorescence at 381 nm, whereas the cyclic ones show dual fluorescence. The long-wavelength emission at 545 nm is significant for the compound with three π-conjugated systems measured at 25 °C. The fluorescence quantum yield and lifetime depend on the number of conjugated systems introduced into the cyclic structure. When the enantiomers of the cyclic compounds is isolated by chiral high-performance liquid chromatography, all of them shows circular dichroism (CD) activity, but only the compound with the three conjugated systems shows CPL with the anisotropy factor g _lum = 4.0 × 10⁻³. On the other hand, this study also synthesizes two cyclic aromatic triamides with the naphthylacetylene unit and succeeded in optical resolutions. The fluorescence quantum yields (Φ = 0.80 and 0.34) are improved, and a single sky blue emission is observed. The CD and CPL anisotropy factors are larger than those of the phenyl counterpart, and the CPL shows a B_CPL value of about 30 M ⁻¹ cm⁻¹.

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