Kurt D. Benkstein

Luminescent sensor molecules based on coordinated metals: a review of recent developments

Abstract Recent developments (1994 to early 1999) in coordination chemistry as they relate to luminescence-based chemical sensing are reviewed. Included are developments involving assemblies for luminescence-based sensing of metal cations, organic and inorganic anions, small neutral molecules in solution, and various volatile organic chemicals. Emphasized in the review are: (a) the chemical features that permit the sensors to function selectively, and (b) the mechanistic schemes that permit analyte recognition and binding events to be converted to luminescence responses.

Luminescent transition-metal-containing cyclophanes (“molecular squares”): covalent self-assembly, host-guest studies and preliminary nanoporous materials applications

Abstract An overview is given of the synthesis and characterization of a family of transition-metal cyclophanes containing rhenium tricarbonyl chloro corners and bridging diimine edges. The synthesis of both heterometallic (Re2M2,M = Pd,Pt) and homometallic (Re4) cyclophanes is described. Also briefly described are studies aimed at shedding light on the probable mechanism of high-yield assembly of homometallic molecular squares. The use of these cavity-containing assemblies as hosts in the condensed-phase binding of selected molecular guests is discussed. Also described are preliminary applications of the compounds as thin film nanoporous sensing elements. These studies suggest that the compounds may prove useful in mass-responsive or light-responsive volatile organic chemical sensing devices.

Shape-selective transport through rectangle-based molecular materials: Thin-film scanning electrochemical microscopy studies

Microporous thin films (≈50 to 400 nm) composed of discrete, cavity-containing molecular rectangles have been prepared. The films, which contain both amorphous and microcrystalline domains, display shape-selective transport behavior. They are permeable to small molecules and to molecules that are short or narrow in at least one dimension—for example, elongated planar molecules—but are impermeable to molecules lacking a narrow dimension. However, the shape selectivity is based on transport through intramolecular rather than intermolecular cavities. By using redox-active probe molecules, rates of transport through the rectangle-based material have been extracted from electrochemical measurements. Spatially resolved measurements obtained via scanning electrochemical microscopy have permitted transport through individual microcrystals to be evaluated semiquantitatively. The measurements reveal that transport is roughly two orders of magnitude slower than observed with thin microcrystalline films of molecular squares featuring similar-sized cavities. The differences likely reflect the fact that cavities within the square-based materials, but not the rectangle-based material, align to form simple one-dimensional channels.

Synthesis and characterization of hexametallic molecular hosts featuring large cavity volumes and constrained cavity port sizes

Abstract The synthesis and characterization of hexametallic host molecules is described. The new molecules utilize 2,2′-bipyrimidine to bridge rhenium(I) tricarbonyls at three points along the short edge of the cavity, and triply functional pyridine-based ligands (2,4,6-tripyridyl-1,3,5-triazine or 1,3,5-tris(4-ethynylpyridyl)benzene) as a top and bottom. Modeling has been done to determine the volumes of the cavities and the sizes of the entry ports for the host molecules.