Selectively Deuterated Liquid Crystalline Cyanoazobenzene Side-Chain Polyesters. 1. Preparation and Characterization of Precursors and Diols

Diphenyl perdeuterated adipate and tetradecanedioate, and three different, selectively deuterium labeled 2-[6-[4-[(4-cyanophenyl)azo]phenoxy]hexyl]-1,3-propanediols have been prepared by exchange and reduction techniques. 1H and 2H NMR spectroscopic investigations have revealed the deuterium exchange in the esters to be higher than 93% and evenly distributed. Similarly, a varying but high deuterium exchange was detected in the selectively labeled diols. All deuterated samples were additionally characterized in detail by 13C NMR spectroscopy; the deuterium isotope effect conclusively assisted some of the shift assignments. No isotope effect could be detected by visible spectroscopy in any of the deuterated diols. On the other hand, FTIR in all deuterated compounds reveals a substantial frequency shift of all carbon-deuteron vibrations as compared to the corresponding carbon-hydrogen vibrations. Polarizing optical microscopic and differential scanning calorimetric investigations have identified all the deuterium labeled diols as monotropic liquid crystals with both nematic and smectic A phases.