The mesogenic behaviours of two azo dye liquid crystals, 1 and 4, differ because of the different length of terminal alkyl chains; azo dye 1 shows a SmB phase, azo dye 4 shows nematic and SmA phases during thermal processing. The molecular stackings of these two azo dye liquid crystals are compared on the basis of crystallographic studies to explain such unexpected mesogenic behaviour.
Complexes have been formed between N,N-disubstituted aminophenylazopyridines and a series of alkoxybenzoic acids by intermolecular hydrogen bonding; liquid crystalline phases of the resulting complexes are induced thereby.
Introductionmoiety. Although we could achieve this purpose by such a strategy, the diversity of the liquid crystalline molecules Azo dye liquid crystals have recently attracted much attention for their potential application in optical is limited, as the CN and NO 2 functional groups are short and no further attachments can be linked to them. storage systems because of their easy availability, good photo-fatigue resistance and the marked transformation Another method for reducing the LUMO and HOMO energy gap is to introduce a heteroaromatic system, such of the molecular shape on E± Z photoisomerizatio n [1, 2]. Azo dyes have a reasonable dichroic ratio and are as the pyridine ring, to replace the benzene carboxylate moiety. Recently, we prepared pyridine-containing azo thus particularly suitable for lower power consumption re ective liquid crystal devices [3]. In a guest-host (GH) dyes by literature methods [7], and found that these compounds showed only highly-ordered smectic transitions; system the dichroic dye is dissolved in a liquid crystal to improve the viewing angle and give better re ectance. however, low viscosity mesogenic phases could be induced by inter-molecular hydrogen bonding with a series of In particular, three-layered GH systems with subtractive colour mixing of yellow, magenta and cyan are expected m-alkoxy benzoic acids [8]. As the pyridine ring can be replaced by other heteroaromatics further to reduce the to be used for developing full colour re ective displays [4]. However, the solubility and phase transition tem-LUMO and HOMO energy gap of the molecules, it may be possible to prepare other heteroaromatic azo peratures of the GH systems are serious problems for applications. Usually, the clearing temperatures vary with dyes with magenta or cyan colours for the development of full colour re ective displays in the future. Although the components of the GH systems. Addition of the non-mesogenic dyes often causes instability of the liquid thermo -mesomorphic H -bonded complexes between pyridyl derivatives and carboxylic acids have already crystalline phase [5]; dyes which are themselves mesogenic minimize this eOE ect. Azo dye liquid crystals are been investigated [9], our diOE erent approach may open up another useful azo dye liquid crystal area. Mesogenic therefore highly desirable as dopants.Previously, we successfully synthesized a series of yellow behaviour in other nitrogen-containing heterocycles with the narrower HOMO and LUMO energy gap can be crystalline azo dyes containing an amino electron-dona ting functionality and a carboxylate electron-withdrawing induced similarly; we now wish to report our completed work. group [6]. To obtain compounds with magenta or cyan colour, i.e. to decrease further the LUMO and HOMO energy gap of the molecules, it may be possible to ...
The molecular stacking and conformation of ethyl 4-{[4-(dodecanoyloxy)phenyl]diazenyl}benzoate was established on the basis of crystallographic data and further compared with those of 4-{[4-(decanoyloxy)phenyl]diazenyl}benzoate and 4-{[4-(octanoyloxy)phenyl]diazenyl}benzoate. The variation of mesogenic behaviors resulting from the different lengths of alkyl chains was also studied.
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