Photoresponsive dendrimers

Photoresponsive dendrimers are of interest because the properties of these materials can be readily modified by an external stimulus. These initial studies have verified that the inclusion of photoactive moieties into dendritic systems does not adversely affect their photochemical response and can enable changes in the overall macromolecular structure. 

Junge DM, McGrath DV, 1997. Photoresponsive dendrimers. Chem Commun (9) 857 858. 

Momotake A, Arai T. 2004b. Synthesis, excited state properties, and dynamic structural change of photoresponsive dendrimers. Polymer 45(16) 5369 5390. 

Thus, a number of photoresponsive dendrimers with photochromic azobenzene units in the exterior, interior, periphery, or whole of the structure have been designed and prepared with different intentions. 

McGrath and Junge [36] reported a photoresponsive poly(aryl ether) dendrimer with azobenzene as the dendrimer core. These dendrimers exhibited reversible trans to cis photoisomerization by irradiation at 350 nm. The authors proposed the use of this type of dendrimer as novel photoswitchable transport vectors. This is based on the expected ability of dendrimers to encapsulate or eject small molecules reversibly upon light perturbation. 

Figure 11.17 Aggregation behavior and photoresponsive properties of an amphiphilic azobenzene dendrimer.

Figure 11.44 (Left) Structures of photoresponsive poly(propylene imine) dendrimers. (Right) The isomerization behavior of pahnitoyl-functionalized amphiphilic dendrimers at the water surface.

Zhang W, Xie J, Yang Z, Shi W. Aggregation behaviors and photoresponsive properties of azobenzene constructed phosphate dendrimers. Polymer 2007 48 4466-4481. 

Case Study 6.1 Supramolecular chemistry - photoresponsive stilbene dendrimers... 

Junge DM, McGrath DV. 1999. Photoresponsive azobenzene containing dendrimers with multiple discrete states. J Am Chem Soc 121 4912 4913. 

Synthesis of a series of azobenzene-cored polyphenylene dendrimers was reported. The photoresponsive properties of these dendrimers were investigated by optieal speetroseopy and gel permeation chromatography The polyphenylene dendrimers exhibit a photoresponsive behavior upon UV and visible light irradiation, resulting in a reversible and appreciable changes of the dendrimer struetures. 

Junge and MeGrath reported studying photoresponse of dendrimers eontaining three interior azobenzene moieties that are radially configured about the eore. With each azobenzene capable of cis-trans isomerization, the... 

The formation of vesicles can also be induced by electrostatic interaction or electrostatic self-assembly. Among others, it was shown that LUVs are obtained when a polycation is mixed with a polyanion-fc-poly(ethylene glycol). The vesicle size can be controlled by changing the polymer concentration. Vesicles are also obtained when a polyanion- -poly(ethylene glycol) is mixed with a cationic azobenzene surfactant. In that case, the vesicles are photoresponsive, that is, they dissemble if the azobenzene is isomerized from the irans form to the cis form. Finally, vesicles can also be prepared by mixing a cationic dendrimer and an anionic sulfonate dye. ... 

Dendrimers belong to a new class of multi-branched macromolecules " and have attracted much attention in recent years as photoresponsive molecules. This interest stems from the fact that the precise placement of a photoactive group in a well-defined macromolecule is possible, and predictable control of the reversible photoinduced molecular change for altering their function can be expected for these molecules. 

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