Eco-friendly blue-fluorescent molecular nanocapsules developed at Tokyo Tech

July 13, 2012

Tokyo, Japan--Tokyo Tech researchers have synthesized blue-fluorescent molecular nanocapsules using inexpensive, eco-friendly zinc and copper ions.

Gail Overton

Blue-fluorescent nanocapsules (copper crystal structure shown) that self-assemble from two metal ions and four bent ligands that include anthracene fluorophores are more eco-friendly and efficient than comparable nanocapsules using precious metal ions like platinum and palladium.

Tokyo, Japan--Tokyo Institute of Technology (Tokyo Tech) researchers have synthesized approximately 1 nm sized blue-fluorescent molecular nanocapsules with an isolated cavity using green and inexpensive, eco-friendly zinc and copper ions. In sharp contrast to molecular capsules and cages composed of precious metal ions such as palladium and platinum that exhibit poor fluorescence, these photo-functional nanocapsules emit blue fluorescence with 80% efficiency and have potential applications in sensors, displays, biomedical imaging, and drug-delivery systems.¹

Molecular cages and capsules can be prepared through a simple synthetic process called coordinative self-assembly. However, most of them are composed of precious metal ions such as palladium and platinum, and are non-emissive due to quenching by the heavy metals. Now, Michito Yoshizawa, Zhiou Li, and co-workers from the Chemical Resources Laboratory at Tokyo Tech Institute of Technology report novel molecular nanocapsules with the M₂L₄ composition (where M represents zinc, copper, platinum, palladium, nickel, cobalt, and manganese). Their zinc and copper capsules, in particular, display unique fluorescent properties. Furthermore, the researchers expect to be able to prepare multicolor fluorescence composites by the simple insertion of appropriate fluorescent molecules into the isolated cavity of the nanocapsules.

The M₂L₄ capsules self-assemble from two metal ions and four bent ligands that include anthracene fluorophores (fluorescent parts). X-ray crystallographic analysis verified the closed shell structures where the large interior cavities of the capsules, around one nanometer in diameter, are shielded by eight anthracene panels.

The zinc capsule emitted strong blue fluorescence with a high quantum yield (80%), in sharp contrast to the weakly emissive nickel and manganese capsules and the non-emissive palladium, platinum, and cobalt capsules. The fluorescence of the copper capsule, on the other hand, depends on the solvent; for example, it shows blue emission in dimethyl sulfoxide but no emission in acetonitrile. This study is the first to show such emissive properties of molecular capsules bearing an isolated large cavity.

REFERENCE:

1. Li Zhiou et al., Chemistry - A European Journal 18,8358 (2012).

SOURCE: Tokyo Institute of Technology; www.titech.ac.jp/english/file/20120712_PressRelease.pdf

About the Author

Gail Overton | Senior Editor (2004-2020)

Gail has more than 30 years of engineering, marketing, product management, and editorial experience in the photonics and optical communications industry. Before joining the staff at Laser Focus World in 2004, she held many product management and product marketing roles in the fiber-optics industry, most notably at Hughes (El Segundo, CA), GTE Labs (Waltham, MA), Corning (Corning, NY), Photon Kinetics (Beaverton, OR), and Newport Corporation (Irvine, CA). During her marketing career, Gail published articles in WDM Solutions and Sensors magazine and traveled internationally to conduct product and sales training. Gail received her BS degree in physics, with an emphasis in optics, from San Diego State University in San Diego, CA in May 1986.