Lasing in a cholesteric liquid crystal doped with derivative of triphenylamine and 1,8-naphthalimide, and optical characterization of the materials

Abstract

Recently derivatives of triphenylamine and 1,8-naphthalimide have been designed and synthesized as materials for organic light emitting diodes and solar cells. We have doped a cholesteric liquid crystal (ChLC) with 1 wt. % of one of the compounds of this series, a day 4-((E)-2-(N-(2-ethylhexyl)-1,8- naphthalimid- 4-yl) vinyl) phenyl) benzenamine (or DG56) and performed optical characterization of the mixture as a material for laser generation. We have obtained such characteristics as light absorption, photoexcitation and fluorescent emission spectra, scalar orientational order parameter S, dispersion dependences of the birefringence, absorption indices, and dichroism for the dye molecules dissolved in the ChLC matrix. A large enough value of S = 0.55 measured for the dye molecules in the ChLC matrix indicates that the molecular planes of the dye are oriented roughly parallel to the nematic molecules. A laser emission from the dye-doped cholesteric with planar orientation showing Grandjean texture is observed at the long-wavelength edge of the cholesteric photon bandgap (PhBG). This confirms a PhBG nature of the laser line and evidences additionally that the dye molecular planes are parallel to the LC molecules. We have also found that the dye-doped ChLC under study represents a promising material for laser generation in ChLC matrices.