Liquid-crystalline self-organization of perylene diimides and subsequent formation of anisotropic thin solid films

Water soluble perylene diimides were synthesized and their aqueous solution properties were examined. Bis-(N,N-diethylaminoethyl) perylene-3,4:9,10-tetracarboxylic diimide dihydrochloride (1) was found to aggregate strongly in water. UV-vis spectroscopy studies indicated the formation of H-aggregates. A spectral blue shift from 530 nm to 500 nm was observed upon increasing the concentration of 1. At approximately 6.7% (w/w) of 1, a liquid-crystalline (LC) phase was observed and identified as a chromonic nematic phase. The LC phase behaviour of 1 was examined by polarized light microscopy (PLM), NMR spectroscopy, and small-angle X-ray diffraction. A columnar hexagonal LC phase was also observed. Nematic LC solutions of 1 were subjected to a shearing force, spreading the liquid onto a substrate and simultaneously aligning the LC domains. This alignment caused an average orientation of the individual dichroic dye molecules. The water in these thin aligned films was then removed, and the anisotropy was transferred to the solid state. The thin solid films on glass substrates were examined by polarized UV-vis and FT-IR spectroscopies and the films displayed properties characteristic of dichroic polarizers. A maximum dichroic ratio of around 30 at 460 nm was observed for a thin sheared film of 1. The structure of the pendant ammonium group of the amphiphile was varied to produce bis-(N,N,2,2-tetramethylamino-1,3-propyl) perylene-3,4:9,10-tetracarboxylic diimide dihydrochloride (2). The aggregation of 2 was observed by UV-vis spectroscopy and was compared to 1. The LC behavior of 2 differed from 1 in the apparent lack of the hexagonal columnar phase. Shearing LC solutions of 2 did not produce anisotropic thin solid films. An amphiphilic quaterrylene diimide (10) was synthesized having the same pendant ammonium group as compound 1. Compound 10 was found to be soluble in formic acid/water mixtures forming a chromonic nematic mesophase at approximately 8% (w/w) in 62% HCOOH (aq.). LC solutions of 10 were oriented by shearing to produce thin solid films that have dichroic polarizing properties at wavelengths between 600 and 733 nm with a maximum dichroic ratio of 20 at 613 nm.