Brinker Nanostructures Research Group

Photoresponsive nanocomposite membranes for nanovalves

Incorporation of covalently-bonded, “switchable” azobenzene ligands as pendant groups within a porous framework is expected to result in nanocomposites with dynamically controllable pore size (Fig. 1), which is of particular interest for nanovalves or molecular gates with potential applications in smart gas masks, membranes, and controlled release as well as new types of externally-controlled micro/nanofluidic channel systems. Such photoresponsive thin film nanocomposites were fabricated by an EISA procedure using Brij56 as the structure-directing agent and TSUA (4-(3-triethoxysilylpropylureido)azobenzene) as the photoresponsive precursor. As determined using TEM and GISAXS techniques (Fig. 2), the photoresponsive nanocomposite membranes exhibited body-centered cubic mesostructure. The size selective photoregulated mass transport of two ferrocene-based molecular probes (FDM and FDMDG) through the membrane to the electrode surface was determined using a chronoamperometry technique. The measured oxidative current increased and decreased in response to alternating UV and visible light exposure, which correlates strongly with the photoisomerization state of the azobenzene ligands (Fig. 3). This indicates that the optically switchable conformation (trans or cis) of azobenzene ligands controls the effective pore size, and, correspondingly, transport behavior on the nanoscale.

References:

Photoregulation of Mass Transport through a Photoresponsive Azobenzene-Modified Nanoporous Membrane, N. G. Liu, D.R. Dunphy, P. Atanassov, Scott D. Bunge, Z. Chen, G.P. López, Timothy J. Boyle, and C.J. Brinker, Nano Letters, 2004. 4(4): p. 551-554.

Photoresponsive Nanocomposite Formed by Self-Assembly of an Azobenzene-Modified Silane, N. G. Liu, Z. Chen, D.R. Dunphy, Y.-B. Jiang, R.A. Assink, and C.J. Brinker, Angew. Chem. Int. Ed., 2003. 42: p. 1731-1734.

Synthesis and crystallographic structures of a novel photoresponsive azobenzene-containing organosilane, N. G. Liu, D. R. Dunphy, M. A. Rodriguez, S. Singer, and C. J. Brinker, Chem. Comm., 2003: p. 1144-1145.

Fig. 1 Schematic drawing of the reversible change in size of azobenzene-modified pores in response to environmental stimuli (light or heat).

Fig. 2 Cross-sectional TEM image and 2D GISAXS pattern (Inset) of a photoresponsive nanoporous membrane.

Fig. 3 The I – t behavior of a photoresponsive nanocomposite film under alternate exposure to UV (360 nm) and visible light (435 nm). Inset is the absorbance at 356–nm (p–p* transition of the trans isomer) of the same film immersed in the buffer solution contained 1 mM FDM.