Mesoporous thin films of "molecular squares" as sensors for volatile organic compounds

Mesoporous thin films of rhenium-based "molecular squares", [Re(CO)(3)Cl(L) ](4) (L = pyrazine, 4, 4'- bipyridine), have been utilized as sensors for v olatile organic compounds (VOCs). The sensing was conducted using a quartz crystal microbalance with the target compounds present in the gas phase at concentrations ranging from 0.05 to 1 mM. Quartz crystal microbalance studi es with these materials allowed for distinction between the following VOCs: (1) small aromatic versus aliphatic molecules of almost identical size and volatility and (2) an array of benzene molecules derivatized with electron donating/withdrawing substituents. The experiments suggest that the mesopo rous host materials interact with VOC guest molecules through both van der Waals and weak charge-transfer interactions. In addition, size selectivity is shown by exposure of the molecular squares to cyclic ethers of differing size.