Guest-host interactions between dichroic dyes and anisotropic hosts

The guest-host interaction between dichroic dyes and anistropic hosts has been investigated by means of optical spectroscopy. Two different TCNQ adducts; 2-{4-[(2,6-dimethylmorpholin-4-yl)(4-metylpiperidin-1-yl)methylene]cyclohexa-2,5-dien-1-ylidene} malononitrile (MORPIP) and 2-{4-[cyclohex-1-yltetrahydropyrimidin-2(1H-ylidene]cyclohexa-2,5-dien-1-ylidine} malononitrile (AMINO) have been examined dispersed in a range of nematic liquid crystal mixtures. The result is a substantial impact on the absorption and luminescence when compared to the situation in isotropic solvents. The excited state decay exhibits a complex behaviour showing a multi-exponential decay of the time-resolved luminescence. The photoluminescence quantum yields of the chromophores, also shows strong host dependence. For AMINO, we observe a trend which is indicative of a viscosity dependence. The observations are discussed in view of different solvent-solute interactions between guest and host.     

Short wave pass and long wave pass dichroic coating at 45° on zinc selenide substrate for dual band thermal imager

In dual band thermal imager dichroic coating plays a vital role in separating 3–5 μm and 7.5–10.5 μm wavelength region for observing better image quality from two different channels. In this work a study has been carried out on the design and fabrication of short and long wave pass dichroic coating at 45° on zinc selenide flat substrate. These dichroic coated optics can be used to separate 3–5 μm (in reflection or transmission channel) and 7.5–10.5 μm (in transmission or reflection channel) wavelength region. An inhomogeneous refractive index profile which is a polynomial of 5th order was considered to design the high and low wave pass dichroic coating on zinc selenide substrate. The inhomogeneous profile was then approximated with five steps from substrate to air medium. These steps were then converted in terms of durable coating materials of six and seven layer stack for short and long wave pass dichroic coating respectively. The coating material combination used was germanium as high index material and IR-F625 as low index material. Result achieved for short wave pass dichroic filter was 94% average transmission in 3–5 μm region and 95% average reflection in 7.5–10.5 μm region. Similarly, result achieved for long wave pass dichroic filter was 95% average reflection in 3–5 μm region and 94% average transmission in 7.5–10.5 μm.     

Synthesis and characterization of side-chain liquid crystalline polymer containing dichroic dye monomer

A series of side-chain liquid crystalline polysiloxanes containing 1-(p-toluidino)-4-anthraquinone undecylenate (TAU) (dye-monomer) and 4-allyloxybenzoyl-4^′-(p-propyl-benzoyl)-p-benzenediol bisate (ABB) (liquid crystalline monomer) side groups were synthesized by copolymeraztion. The molecular structures of the monomers and polymers were confirmed by FT-IR spectroscopy. The optical characterization of the monomer ABB and polymers was made by using polarizing optical microscopy (POM) technique, and their thermal behaviour was investigated by thermogravimetric analyses (TGA) and differential scanning calorimetry (DSC). The conjugate action of the dye (1-(p-toluidino)-4-hydroxyl anthraquinone) and the monomer was analyzed by fluorophotometry. Polymers and monomer ABB revealed nematic phase. And DSC results demonstrated that the glass transition temperatures (T_g) of the polymers increased with the increase in dye-monomer. TGA result showed that the temperatures at which 5% mass loss occurred () for all the polymers were above 270 °C.