Preparation and properties of self-assembled resorcinarene monolayers

Abstract

Several resorcinarene and calixarene based receptors were synthesised with the overarching aim of developing selective hydrocarbon sensors for application in the petroleum exploration industry.Thioacetyl resorcinarenes functionalised at the upper rim with methoxy, propoxy and benzyloxy groups were synthesised, along with a methylene bridged cavitand. Similar hydroxy and methoxy resorcinarenes functionalised at the lower rim with decylsulfide groups were prepared, along with a p-tert-butylcalix[4]arene thiol derivative.The receptors were allowed to self-assemble on gold substrates, and the resulting surfaces were characterised by contact angle, polarised modulation infrared reflection absorption spectroscopy (PMIRRAS), and atomic force microscopy (AFM). The results indicated that all but one of the receptors form monolayers. The exception, a resorcinarene decyl sulfide, appears to form a bilayer or multilayers.AFM force spectroscopy was used to investigate the receptor properties of the monolayers by using tips functionalised with adamantyl, cyclohexyl and benzyl molecular probes. A quantity of a deep cavitand was obtained to use as a comparison to the shallower receptors synthesised.Specific interactions were observed between the benzyloxy and methylene cavitand monolayers and the adamantyl probes. These monolayers along with the methoxy resorcinarene monolayer also showed significant interactions with the cyclohexyl probes. These receptors present promising targets for further studies of the complexation behaviour of resorcinarene based receptors and cyclic aliphatic hydrocarbons.All surfaces exhibited interactions with the benzyl probes. The propoxy resorcinarene and deep cavitand monolayers appear to show selectivity towards the benzyl probes with no interactions observed for the adamantyl or cyclohexyl probes.The binding of the monolayer was found to be influenced by not only the macrocylic receptor site, but also the monolayer structure. Evidence for this was provided by the difference in binding exhibited by the methoxy resorcinarene thiol monolayer and the methoxy resorcinarene decylsulfide monolayer.