Ordering Nanoscale Dots with Molecular Honeycombs

1. Ordering Nanoscale Dots with Molecular Honeycombs Designable Porous Organic Networks Represent A New Strategy for Nanoparticle Assembly Ultrasmall semiconductor particles, so-called “quantum dots,” have tunable optical and electronic properties that derive from their nanometer-scale size. Scientists have long hypothesized that ordered arrays of nanoparticles with precisely controlled spacing will have enhanced properties that are ideal for a variety of applications, including the production of high efficiency solar cells. The challenge has been assembling millions of tiny dots in the desired structures. Researchers at Cornell have developed a method that uses covalent-organic frameworks (COFs) — huge organic molecules that resemble nm-size honeycombs — to create ordered arrays of quantum dots. In the absence of the honeycomb, the 3-nm-diameter quantum dots float freely in solution, leading to a pronounced orange color (image at right). When honeycombs (COFs) are dropped into the beaker, the quantum dots spontaneously file into the nm-scale openings where they become trapped in the 4.7 nm hexagonal pores. As a result, the orange color in solution quickly fades. The honeycombs, however, take on a deep red color consistent with correct ordering of the dots. This finding may enable the development of high performance hybrid materials for solar cells. Quantum dots in solution Quantum dots introduced into COF Visit the CCMR online at http://www.ccmr.cornell.edu Research supported by NSF DMR-1120296