Light-Controllable Chiral Photochromic Multifunctional Liquid Crystal Polymers
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Light-Controllable Chiral Photochromic Multifunctional Liquid Crystal Polymers Valery P. Shibaev, Alexey Yu. Bobrovsky, Natalia I. Boiko Chemistry Department, Moscow State University Lenin Hills, 19899 Moscow, Russia
ABSTRACT A new family of light-controllable chiral photochromic multifunctional liquid crystalline (LC) side-chain acrylic polymers consisting of nematogenic, chiral and photochromic monomer units was obtained. The new principle of photoregulation of the helical supramolecular structure and optical properties of the binary and ternary chiral photochromic LC polymers based on the change of helical twisting power of the chiral photochromic monomer units was developed. The features of photooptical behaviour of LC polymers possessing the dual photochromism and the peculiarities of optical data recording based on the photochemical spectral gap burning were presented and discussed. The synthesized polymers are shown to be promising candidates for colour data recording and storage.
INTRODUCTION The macromolecular chain structure of polymers offers almost unlimited options in the molecular design when one macromolecule may contain different monomer units displaying the own functionality. Among the different types of polymers the chiral photochromic side-chain liquid-crystalline (LC) polymers are of significant interest due to the combination of mesogenic, chiral and photochromic groups predetermining the helical supramolecular LC structure formation which is very sensitive to the light irradiation [1, 2]. These photoactive chiral LC polymers attract the scientific and applied interest of modern material chemistry as new smart materials with light-controllable supramolecular structure and optical properties [3, 4]. The principle of the creation of such polymers is based on the synthesis of multifunctional LC side-chain acrylic copolymers consisting of nematogenic monomer units (favourable to the nematic phase formation), chiral fragments (contributed to the nematic phase twisting and helical supramolecular structure formation) and photochromic groups provided the photosensitivity to the copolymers. Chiral and photochromic groups may be combined in the same monomer unit (binary copolymers (figure1a) or they may be included in the macromolecule as the individual (or combined) monomer units (ternary copolymers, figure 1b,c). In this paper the main approaches to the synthesis of a series of novel acrylic copolymers, containing different mesogenic, chiral and photochromic groups are considered and the results of the study of the phase behaviour, structure as well as photochemical and photooptical properties of these copolymers are discussed.
CC4.4.1
(a)
Mesogenic group
(b)
(c)
Photochromic group
Chiral group
Figure 1. Schematic representation of multifunctional chiral photochromic LC copolymers
EXPERIMENTAL DETAILS Synthesis of polymers and their characterization All monomers were synthesized according to the procedures described in our papers [58]. The chiral photochromic copolymers were prepared by radi
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