Carbosilane liquid crystalline dendrimers: From molecular architecture to supramolecular nanostructures

A systematic study of the influence of generation number on the phase behav ior of LC dendrimers is presented. For this purpose, phase behaviors and st ructures of first to fifth generations of liquid crystalline (LC) carbosila ne dendrimers with 8, 16, 32, 64, and 128 terminal cyanobiphenyl groups wer e investigated. Investigation of thermal behavior of the LC dendrimers by m eans of polarizing optical microscopy, differential scanning calorimetry, a nd X-ray diffraction experiments reveals smectic-type mesophases over a wid e temperature region. It is shown that, with increasing generation number t he isotropization temperature increases whereas the enthalpy of this phase transition decreases. The strongest influence of spherical molecular archit ecture on the phase behavior of the LC dendrimers appears at high generatio ns. In the case of LC dendrimer of the fifth generation, it leads to the fo rmation of two levels of a structural organization. This dendrimer forms di fferent supramolecular nanostructures of columnar type in addition to smect ic-like arrangement of mesogenic groups. Possible structures of all mesopha ses formed are discussed.