Highly efficient luminescence dyes based on pyrene and anthracene derivatives (see figure) are synthesized for liquid crystal dye lasers. The threshold value of one of the pyrene derivatives is as low as 1/20 that of the commonly used DCM in cholesteric liquid crystal (CLC) distributed feedback lasers. Good optical properties such as luminous efficiency and solubility in CLCs are important factors for realizing a low threshold.

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The authors have studied low threshold lasing in dye-doped cholesteric liquid crystals (CLCs). We designed and synthesized a dye, 1,3,6,8-tetrakis(6'-hexyloxy-2-naphthyl)pyrene, which has high quantum yield Φ= 0.85. Since the transition dipole moment is perpendicular to the local director of a host CLC, laser oscillation occurs at the higher energy edge of the stop band of CLC contrary to that in conventional dyes aligning parallel to the director. We evaluated lasing characteristics and found that the pyrene-doped CLC gives laser threshold of 43 nJ/pulse, which is about one order of magnitude lower than that of conventional laser dyes.

We synthesized novel liquid crystalline molecules that contain a bis(biphenyl)diacetylene mesogen and confirmed their structures by 1H NMR, 13C NMR, and FT-IR spectroscopy and mass spectrometry. These compounds formed thermotropic liquid crystals in a wide temperature region that was well characterized by optical microscopic and X-ray measurements.