Abstract
Most triazine-based liquid crystalline (LC) dendrimers reported thus far are the main-chain LC macromolecules with long flexible chains at their periphery and attached to internal rigid or semi-rigid frameworks. Their formation of mesogenic phases often depends on the intermolecular face-to-face π–π interactions between dendritic molecules, which are unusual. Their mesogenic phases can also be formed by incorporation of mesogenic units to the dendritic skeletons through long flexible chains, as most side-chain LC dendrimers, in which the peripheral mesogenic units generally play the important roles. For main-chain triazine-based dendrimers, their morphology is maintained by restricted freedom of rigid or semi-rigid connecting units, and their formations of LC phases are therefore not straightforward to be controlled. In this review, we thus describe modulating of the intermolecular face-to-face π–π interactions between the triazine-based dendritic molecules, with the aim of forming LC phases through molecular design.
Highlights
Since the discovery of dendrimers in the late 1970s, [1] there has been substantial development in their synthesis and study of their physical properties
liquid crystal (LC) dendrimers can generally be divided into side-chain dendrimers in which the mesogenic units are incorporated at the periphery of molecules and main-chain dendrimers in which the mesogenic moieties are designed as linking moieties within the internal framework
In contrast to side-chain LC dendrimers in which the LC phases are mostly induced by the peripheral mesogenic units, both the rigid or semi-rigid internal frameworks and flexible peripheral chains are all important in inducing mesophases for the main-chain LC dendrimers [2,36,37], and this leads the formation of mesophases of the main-chain LC dendrimers to be difficult to control
Summary
Since the discovery of dendrimers in the late 1970s, [1] there has been substantial development in their synthesis and study of their physical properties. The mesogenic units are important in inducing their LC behavior, and this type of LC dendrimer mostly consists of PMAMA (polyamidoamine), PPI (polypropylimine), Si-derivatives (siloxanes, carbosilanes, and carbosilazanes), and polyester as their dendritic network, all of which have been reviewed extensively [2,35,36,37,38] Special functional moieties, such as fullerene and ferrocene, may be incorporated in side-chain LC dendrimers for particular properties as reported in literatures [2,36,39]. Kotha and colleagues prepared 1,3,5-triphenyl-sare1,3,5-triamino-s-triazine incorporated at the periphery of molecules and main-chain dendrimers in which the triazine-based dendrimers, which exhibited a columnar phase after being mixed with mesogenic moieties are designed as linking moieties within the internal framework.
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