Photoresponsive block copolymers containing azobenzenes and other chromophores

Abstract

Photoresponsive block copolymers (PRBCs) containing azobenzenes and other chromophores can be easily prepared by controlled polymerization. Their photoresponsive behaviors are generally based on photoisomerization, photocrosslinking, photoalignment and photoinduced cooperative motions. When the photoactive block forms mesogenic phases upon microphase separation of PRBCs, supramolecular cooperative motion in liquid-crystalline PRBCs enables them to self-organize into hierarchical structures with photoresponsive features. This offers novel opportunities to photocontrol microphase-separated nanostructures of well-defined PRBCs and extends their diverse applications in holograms, nanotemplates, photodeformed devices and microporous films.

Figure 1

Microphase separation of AB-type PRBCs with well-defined structures.

Figure 2

Scheme of preparation of well-defined PRBCs by direction polymerization.

Figure 3

Preparation of amphiphilic PRBCs by a modified ATRP method.

Figure 4

Schematic illustration of PRBCs prepared by post-functionalization.

Figure 5

Scheme of PRBCs prepared from a special reaction.

Figure 6

Properties of AZ-containing PRBCs inherited from AZ homopolymers. A is the absorption of AZs, θ represents the angle between the polarization direction of the linearly polarized light and the transition moment of an AZ moiety.

Figure 7

Photoresponsive properties of coumarin, cinnamate and spiropyran derivatives.

Figure 8

Photoinduced MCM and SMCM of PRBCs. A PRP forms the majority phase (a) and the minority phase (b), respectively. (c) A photograph of a PRBC film with 200 μm thickness (left) and scheme of the recorded Bragg grating (right).

Figure 9

POM images and possible smectic LC layer structures of PEO-based PRBCs.

Figure 10

Wormlike nanostructures obtained in a PRBC showing an LC phase.

Figure 11

Schematic illustration of a well-defined PRBC and a random copolymer with a similar chromophore content (about 22 mol %).

Figure 12

Schematic illustration of supramolecular cooperative motion in LC PRBCs.

Figure 13

Perpendicular array of nanocylinders and photoresponsive mesogens in a PRBC film by thermal annealing.

Figure 14

Fabrication of a parallel nanocylinder array in a PEO-based PRBC by the mechanical rubbing method.

Figure 15

Photoalignment of microphase-separated nanocylinders in an LC PRBC.

Figure 16

Control of nanocylinders in PRBCs by electric (a) and magnetic fields (b).

Figure 17

Holographic gratings recorded in PRBCs and enhancement of surface relief upon microphase separation.

Figure 18

Enhancement of surface-index modulation in PRBCs with photoresponsive groups in the minority phase. (A, aligned, R, random).

Figure 19

Mechanically tunable fringe spacing of gratings recorded in an ABA-type PRBC with thermoplastics.

Figure 20

Schematic illustrations of recording and reading processes in volume storage based on PRBC materials.

Figure 21

Nanotemplate applications of PRBCs. (a) Fabrication of periodic array of Ag nanoparticles. (b) Anisotropic ionic conduction in nanochannels. (c) Selective absorption of Au nanoparticles. (d) Preparation of SiO₂ nanorod arrays by combination of a sol-gel process with PRBC lithography.

Figure 22

Schematic illustration of reversible dissociation and formation of PRBC micelles upon photoirradiation.

Figure 23

Fabrication of regularly patterned micropores with an amphiphilic PRBC by spin coating under a dry environment.