Chiral Polymorphic Hydrazine-based Asymmetric Liquid Crystal Trimers with Resorcinol as Linking Group

Introduction:
This is the first report on chiral polymorphic hydrazine-based asymmetric liquid crystal
trimers, 1-[4'-(4''-(5-Cholesteryloxy)carbonyl)butyloxy]-3-[N-benzylideneoxy-N'-(4'''-decyloxybenzylidene) hydrazine]
butyloxybenzenes, and 1-[4'-(4''-(10-cholesteryloxy)carbonyl)nonyloxy]-3-[N-benzylideneoxy-N'-(4'''-
decyloxybenzylidene)hydrazine]butyloxybenzenes., in which the hydrazine and cholesterol arms were connected
via two flexible methylene spacers (n = 3-12 units and m = 4 or 9, respectively) to the central resorcinol core.


Materials and Methods:
FT-IR, 1D and 2D NMR spectroscopy, and CHN microanalysis were used to elucidate
the structures of the trimers. Differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction
were used to study the transitional and phase properties of the trimers, which were length and spacer parity
dependent. Trimers with short spacer length in the cholesteryl arm, m = 4 showed an interesting phase sequence
of BP/N*-TGBA*-SmA*.


Results and Discussion:
The TGBA* phase was sensitive to spacer length as it was only observed in trimers with
short ester linkage. For the long analogues, m = 9, characteristic visible reflection and a much simpler phase sequence
with only N* and SmA* phases were observed.


Conclusion:
The X-ray diffraction measurements revealed that layer periodicities of the SmA* phase were approximately
half the estimated all-trans molecular length (d/L ≈ 0.44-0.52), thus suggesting that the molecules
are either strongly intercalated or bent.