Directed assembly of inorganic polyoxometalate-based micrometer-scale tubular architectures by using optical control.

The self-assembly of supramolecular architectures to produce functional systems and devices is a key goal where molecular design, self-assembly, and materials design need to be combined together. In polyoxometalate chemistry we have taken the challenge to understand the assembly of clusters from the molecular to the nanoscale, by using a range of approaches including control of the available species and the use of macroscale flow systems. This type of control is vital, especially if the link from the nanoscale to themesoscale (and beyond) is to be made. Nature can solve this problem by constructing a scaffold to direct the assembly processes. By using this strategy, scaffolding allows complex structures to be assembled and self-correction ensures the formation of precise, highly complex architectures. However, even these systems displace the problem to the design of the scaffold that must be replaced in synthetic systems. Routes to accomplish this from the bottom up are limited because controlling the structures formed on longer length scales is extremely demanding. The associated dynamic range currently requires specialist equipment for fabrication, and reliable new material and device architectures are difficult and time consuming to fabricate. As such, the discovery of a strategy for the controllable and reliable fabrication of materials that bridges the gap between bottom-up self-assembly and topdown control would revolutionize the design and fabrication of mesoscopic materials. Herein we report the use of local convective flow fields to direct the bottom-up growth of self-assembling nanometersized inorganic building blocks into micrometer-sized tubes, by injecting solutions of polyoxometalate clusters into a bulk solution containing a large organic cation. The resulting millimeter-sized network materials can be structured from the top down, by using polyoxometalate clusters assembled from the bottom up (Figure 1). The basic building