Coumarin-based emissive liquid crystals

Abstract

Calamitic luminophores are presented based on an elongated aryl-substituted coumarin core. The substitution pattern at terminal and lateral positions were systematically modified. The new compounds exhibit smectic C and/or nematic liquid crystalline phases. The chromophores show fluorescence in the blue spectral region. The benzopyranones are miscible with acrylate-substituted reactive nematic mesogens. Uniaxial orientation of the mixed systems was achieved by surface-assisted alignment on polyimide orientation layers. The film anisotropy was stabilised by subsequent photocrosslinking. The crosslinked oriented films display linear polarised photoluminescence upon isotropic excitation.

Keywords:

• coumarin
• liquid crystal
• calamitic
• fluorescence

Notes

1. The reactive mesogens 8 and 9 were obtained from SYNTHON Chemicals GmbH Wolfen, Germany.

2. The smectic phase forming coumarins 5 and 6 have not been investigated in detail in mixtures with the reactive mesogens 8 and 9. For example, compound 5c showed incomplete miscibility with the diacrylate 8 already at a content of 10wt%.

3. The fluorescence quantum yield of the coumarin 4g was determined in CHCl₃ solution at a wavelength of 347 nm referenced to quinine sulphate in dilute sulphuric acid according to standard procedures.[62] The calculation gave a value of Φ_F = 0.76.