Liquid crystalline properties of azobenzenes: I. 4-methoxy-, 4-ethoxy-, 4-propoxy- and 4-butoxy-4 '-alkyloxyazobenzenes

Liquid crystalline properties of four series of azobenzenes, 4-methoxy-4'-a lkyloxyazobenzenes (azo-1-n), 4-ethoxy-4'-alkyloxyazobenzenes (azo-2-n), 4- propoxy-4'-alkyloxyazobenzenes (azo-3-n) and 4-butoxy-4'-alkyloxyazobenzene s (azo-4-n), were investigated. By polarizing microscopy nematic and smecti c C mesophases were detected. By DSC and TOA thermo-optics the parameters o f phase transitions were measured. A typical odd-even effect of the clearin g temperature was found. No smectic phase was detected in the first three s eries, even for the longest alkyloxy chains. The smectic C appears for the first time in the butoxy family, starting from the undecyloxyl derivative. In each series a polymorphism in the solid state was detected, especially s ignificant in the propoxy and butoxy family, that was explained in terms of the ODIC phases.