Aromatic hydrocarbon belts (AHCBs) have fascinated scientists for over half a century because of their aesthetically appealing structures and potential applications in the field of carbon nanotechnology. One of the enduring challenges in synthesizing AHCBs is how do we cope with the build-up of energy in the highly strained structures during their synthesis? Successful preparations of AHCBs offer the prospect of providing well-defined templates for the growth of uniform single-walled carbon nanotubes-a long-standing interest in nanocarbon science. In this Review, we revisit the protracted historical background involving the rational design and synthesis of AHCBs and highlight some of the more recent breakthroughs, with emphasis being placed on the different strategies that have been used for building up curved and fused benzenoid rings into molecular belts. We also discuss the scientific challenges in this fledgling field and provide some pointers as to what could transpire in years to come.

Aromatic hydrocarbon belts.

The sensitivity of vase-like cavitands to nitrobenzene and other organic and inorganic vapours has been investigated by using the technique of the quartz microbalance (QMB) in order to determine the variation of the mass adsorbed. Cavitands at room temperature showed a high selectivity to nitrobenzene with respect to benzene and other organic vapours like toluene, fluorobenzene and carbon tetrachloride. This material is insensitive towards other vapours, present in a concentration of 1000 ppm, like H 2 , CO, SO 2 , H 2 S, NO and NO 2 , an it is also insensitive to relative humidities up to 90%. The X-ray structure analysis of the host—guest complex with the fluorobenzene is also described.

Cavitands as selective materials for QMB sensors for nitrobenzene and other aromatic vapours

Cavitand-coated quartz-crystal microbalance (QCM) transducers present selective response toward organic vapours (mainly aromatic and chlorinated hydrocarbons) and toward organic analytes in water. The different behaviour of cavitands 1 and 2 as molecular receptors for organic vapours points out the selective response of cavitand 1, due to the presence of a preorganized cavity.

Selective detection of organic compounds by means of cavitand-coated QCM transducers

Five octaethylporphyrins (OEP) and tetraphenylporphyrins (TPP): (OEP)InCl, (OEP)MnCl, (OEP)GaCl, (TPP)Pd, and (TPP)RhI have been deposited as sensitive coating onto quartz-crystal microbalances. The sensitivities of the resulting sensors have been measured with respect to 2,4-dinitrotrifluoromethoxybenzene vapors. When exposed to the nitroaromatic compound, a large and significative response is recorded for every tested porphyrin, the detection process being slightly reversible. Along with a good sensitivity, the sensors exhibit an excellent selectivity when common solvents are used as interfering vapors. Among all the studied derivatives, (OEP)MnCl appears as the most sensitive and selective coating.

Metalloporphyrins as sensing material for quartz-crystal microbalance nitroaromatics sensors

In Anlehnung an den in Band 16 erschienenen Beitrag uber Chemo- und Biosensoren zur Messung in Flussigphasen soll im folgenden eine einfuhrende Darstellung der wichtigsten Gassensoren gegeben werden. Es wurden dabei solche Sensoren berucksichtigt, die zum einen kommerzielle Bedeutung erlangt haben, zum anderen werden aber auch die Sensoren genannt, die sich, dem derzeitigen Stand der Technik nach, noch weitgehend im Stadium von Forschung und Entwicklung befinden.

M A F Elmosalamy

Papers

Studies on two epoxyoctacosahydro[12]cyclacene derivatives as sensor coatings on quartz piezoelectric crystals for detecting aromatic vapours