Enhanced Ordering and Efficient Photoalignment of Nanostructures in Block Copolymers Enabled by Halogen Bond

Abstract

Fabrication and manipulation of macroscopically ordered nanostructures in polymer films via supramolecular selforganization are fascinating from the viewpoints of science and technology. Here, a halogen bond (XB) was introduced into a block copolymer to facilitate its microphase separation process upon XB-driven supramolecular self-assembly. To the best of our knowledge, this is an extremely rare example to elegantly maneuver nanostructures of polymers by the emerging supramolecular interaction, XB. The nonmesogenic block copolymer composed of poly(ethylene oxide) and azopyridine-containing polymethacrylate was transformed into a supramolecular liquid-crystalline polymer through the halogen-bonded interaction between 1,2-diiodo-3,4,5,6-tetrafluorobenzene and the azopyridine group with the optimal molar ratio of 1:1. For comparison, one hydrogen-bonded liquid-crystalline polymer was also fabricated but no such ordering enhancement was acquired, indicating that both the high directionality of XB and the resulting supramolecular mesogenic ordering played key roles in the enhanced ordering of nanostructures in polymer films. In addition, efficient photoalignment and photoreorientation of nanostructures coinciding with the oriented direction of the supramolecular mesogens were also obtained by manipulating photoirradiation of linearly polarized light for the present XB-involved liquid-crystalline block copolymer, which is promising for the development of a novel generation of advanced composite liquid crystal (LC) materials.

Halogen bonding regulated functional nanomaterials

“…(a) 2,9-BHP; (b) 2,9-BHPO; (c) 3,8-BHP; (d) 3,8-BHPO. Figure reproduced with permission from ref 119. Copyright 2020, American Chemical Society.…”

Halogen bonding in polymer science: towards new smart materials

“…For this purpose, a pyridyl azobenzene motive was introduced into a polymeric structure. 47 The side chain attached azo pyridine units also provide the pyridine nitrogen as XB-acceptor. Due to complexation with 1,2-diiodo tetrafluorobenzene the material showed a high tendency to form ordered microstructure in polymer films.…”

Recent Developments in Polymeric Assemblies and Functional Materials by Halogen Bonding

“…The copolymer film and its halogen bonded complex actively responded in periodic writing/erasing experiments, when exposed to 405 nm linearly polarized/circularly polarized laser, indicating their promising potential in optical data storage applications. Recently, Yu and co‐workers have introduced liquid‐crystalline properties into a non‐mesogenic block copolymer composed of poly(ethylene oxide) and azopyridine‐pendant polymethacrylate ( PEO‐ b ‐PAzPy ) by co‐assembly with an additive 1,2‐diiodotetrafluorobenzene ( 1 , 2‐DITFB ) (Figure 3A) [36] . Halogen bonding between the nitrogen atom of the AzPy acceptor and the iodine atom of 1, 2‐DITFB donor conferred macroscopically ordered nanocylinder arrays in polymer films that displayed smectic‐A (SmA) phase behavior.…”