A HELICAL POLY(AMINO ACID) HAVING CARBAZOLE SIDE-CHAINS - A CANDIDATE FOR A PHOTOELECTRIC LIQUID-CRYSTAL .3. A CONFORMATIONAL STUDY

The conformation of a carbazole-substituted poly( alpha -amino acid), poly(N** epsilon -(carbazolyl-carbonyl)-L-lysine) (PKL), has been studied in solid films and solutions by fourier transform infrared spectroscopy. In all samples investigated the main chain assumes the alpha -helical conformation. The side chains are strongly hydrogen bonded in the solid state, with approximately 20% unbounded groups. A side-chain conformation is proposed, where the major part of the side chains are stacked in three stacks almost parallel to the molecular axis. The average stack length exceeds 10 units and can in principle be infinite. The carbazole groups in the stacks are efficiently locked-in conformationally in a structure which probably favors effective energy transfer and photoconduction. In solution the hydrogen bonding of the side chains is disrupted.