Liquid Crystals. Iam-Choon Khoo

Liquid Crystals - Iam-Choon Khoo


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target="_blank" rel="nofollow" href="#ulink_777f1bdc-859f-5d71-812c-57a39df57a49">Figure 1.2. Molecular structure of a heterocyclic liquid crystal.

      In general, optical properties of liquid crystals fall into two distinct categories: those characteristics of individual constituent molecules and those unique to the bulk crystalline mesophases. Here we discuss optical properties that are largely decided by the individual constituent molecules; optical properties associated with various ordered mesophases of liquid crystals are elaborated in later chapters.

      1.2.1. Electronic Optical Transitions and UV Absorption

      In general, these transitions correspond to the absorption of light in the near‐UV spectral region (≤200 nm) [2]. These results for a benzene molecule can also be used for interpreting the absorption of liquid crystals containing phenyl rings. On the other hand, in a saturated cyclohexane ring or band, usually only σ electrons are involved. The σσ * transitions correspond to absorption of light of shorter wavelength (≤180 nm) in comparison to the ππ * transition mentioned previously.

      1.2.2. Visible and Infrared Absorption; Terahertz, Microwave


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Librs.Net
n // n Δn α// (cm−1) α (cm−1)
1.75 1.525 0225 (λ = 0.589 μm)
1.71 1.50 0.21 (λ = 1.55 μm)
1.70 1.49 0.21 55 40 (λ = 10.59 μm)
1.73 1.57 0.9 3.1 (0.2 THz)
1.76 1.62 7 27 (2 THz)