Journal zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA of zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Molecular Structure, 218 (1990) 309-314 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands 309 FTIR LINEAR DICHROIC SPECTRA OF SUBSTANCES DISSOLVED AND ORIENTED IN A NEMATIC LIQUID CRYSTAL M. HELHAKEM and B. JORDAXOV Bulgarian Academy of Sciences, Institute of Organic Chemistry, RG1113 Sofia SUMMARY Some opportunities for studying linear dichroic FTIR spectra of molecules dissolved and oriented in a nematic liquid crystal of very poor IR spectrum (Merck ZLI-1538) are presented. The method allows one to obtain in a simple man- ner direct information about the symmetry properties of the IR transitions of the dissolved molecules, Some suitable examples are given, INTRODUCTCOI'J Sonr authors (refs. l-4) demonstrated the use of anisntr0pi.c solvents jn the optical polarization spectroscopy. They have shown that such solvents induced a partial orientation in the dissolved molecules and related the polarl.zation da- ta obtained from the measured polarized spectra to the symmetry properties of the dissolved free molecules, thus considerin? them as isolated, Stretched poly- mers have much more frequently been used than nematic liquid crystals for the purposes of the orientation. This is because the majority of the most popular and used liquid crystals possess numerous intense 'CR bands leadinp to strong: overlapping with the IR absorption hands of the studied solute molecules, In the offered pa?er we present some results of our attempts to make the nematic liqui- de crystals more popular and usable as anisotropic solvents in the polarization spectroscopy. The limitations arising from the strone absorp:ion can fortunately be overco- me since some little known and used liquid crystals turn out to possess a poor IR spectrum fully comparable to that of polyethylene (PF:) or nujol, Thus our choice felt on the liquid crystal ZLI-1538 (Merck) representing trans-trans-4- n-butyl-4' -cyanohicyclohexyl with nematic range 5%79'C. Its IR spectrum is dis- -1 played in Fig, 1. As seen only the 2800-3100 cm region can not he used hecause of the strong aliphatic CH absorption, We found that ZLI-1538 is a Bond solvent for a wide scale of compounds and the ohtained solutions preserved their nematic properties at relatively high concentrations (typically 5-15X), This permAtted us to take spectra even with the routine FTIR parameter set corresponding to 32 scans and 2 cm-' resolution. In contrast to the stretched polymer technique (ref. 3) the orientation of the nematic solutions is achieved in a very simple way by rubbing and polishing the IR cell windows in one direction, 0022-2860/90/$03.50 0 1990 Elsevier Science Publishers B.V.