Photoresponsive Block Research Articles

Lubricant Effect of Flexible Chain in the Photoinduced Motions of Surface-Grafted Liquid Crystalline Azobenzene Polymer Brush

Poly(hexyl methacrylate)-block-poly[4-(10-methacryloxydecyloxy)-4′-pentylazobenzene] (PHMA-b-P5Az10MA) diblock copolymer brush was stepwisely synthesized on an initiator-immobilized quartz surface by atom transfer radical polymerization. In this chain design, a flexible PHMA chain was connected between a liquid crystalline (LC) azobenzene (Az) block and a solid substrate. The orientation and structural features of the smectic layer spacing of the azobenzene (Az) block at the outer surface were essentially the same as those of P5Az10MA homopolymer brush. Upon irradiation of 436 nm linearly polarized light (LPL) at a temperature of liquid crystalline (LC) state of the Az polymer, the block copolymer brush exhibited a significant improvement in the induction of in-plane optical anisotropy compared to a corresponding homopolymer brush as revealed by UV–vis spectroscopy and grazing angle incidence X-ray diffraction measurements. The temperature dependence of the optical and structural anisotropy and photoreorientation behavior unveiled a significant lubricant role of the flexible chain block for the improvement of photoresponsive motions. This work proposes an idea to decouple the photoinduced motions of the upper photoresponsive block from the restriction by the substrate through introduction of a “buffer spacer” chain.

Photonic Crystals: Photoresponsive Block Copolymer Photonic Gels with Widely Tunable Photosensitivity by Counter‐Ions (Adv. Mater. 23/2012)

Block copolymer photonic gels exhibiting multiple colors in response to near-UV radiation are demonstrated by Y. Kang and co-workers on page OP 127. The counterions pairing with the polyelectrolyte in the gel layers determine the photosensitivity of photonic gels. The simple replacement of ions can make the photonic gels either highly sensitive or insensitive to near-UV. The illustration shows ionic signaling giving “STOP” and “GO” cues for the photoresponse of these photonic gels.

Photoresponsive Block Copolymer Photonic Gels with Widely Tunable Photosensitivity by Counter‐Ions

Block copolymer photonic crystals comprising polyelectrolyte hydrogels exhibit strong reflective multicolors in response to near-UV radiation. Due to unique volume transition of swollen gels, the photonic gels show high photosensitivity, and which can be widely tunable by exchanging counter-anions. Multicolor photonic patterns created by photolithography can be repeatedly fixated and reactivated by sequentially exchanging counter-anions with different photosensitivity.

Doubly photoresponsive and water‐soluble block copolymers: Synthesis and thermosensitivity

AbstractWe report the synthesis and investigation of a new type of photoresponsive block copolymers (BCPs). They were designed to comprise two water‐soluble polymers containing two different photoisomerizable moieties (either azobenzene and spiropyran or two different azobenzenes), with the two constituting blocks that, when separated, exhibit a lower critical solution temperature (LCST) in water and can shift their LCST in opposite directions upon photoisomerization (decrease of LCST for one polymer and increase for the other). A variety of such doubly photoresponsive BCPs were synthesized using either azobenzene‐ or spiropyran‐containing poly(N,N‐dimethylacrylamide) (PDMA), poly(N‐isopropylacrylamide) (PNIPAM) and poly[methoxydi(ethylene glycol) methacrylate] (PDEGMMA). Their thermal phase transition behaviors in aqueous solution before and after simultaneous photoreactions on the two blocks were investigated in comparison with their constituting blocks, by means of solution transmittance (turbidity) and variable‐temperature 1H NMR measurements. The results show that BCPs displayed a single LCST whose shift upon two photoisomerizations appeared to be determined by the competing and opposing photoinduced effects on the two blocks. Moreover, optically controlling the relative photoisomerization degrees of trans azobenzene‐to‐cis azobenzene and spiropyran‐to‐merocyanine could be used to tune the LCST of BCP solution. This study demonstrates the potential of exploring a more complex photoreaction scheme to optically control the solution properties of water‐soluble thermosensitive BCPs. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4055–4066, 2010

Photoresponsive Block Copolymers Containing Azobenzenes and Other Chromophores

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.