Mixed monolayer LB films of EHO and calix[8]arene

The functional properties of Langmuir-Blodgett (LB) films of many organic dyes, such as porphyrins and phthalocyanines, may be enhanced using a host material that forms a deposition vehicle for the preparation of LB assemblies of improved uniformity. Furthermore, the presence of the structural matrix often leads to the modification of the functionality of the hybrid material itself. Here, the effect of a host matrix on the LB deposition, UV-visible spectra and gas-sensing properties of 5,10,15,20-tetrakis[3,4-bis(2-ethylhexyloxy)phenyl]- 21H,23H-porphine (EHO) has been investigated. The host material used is a carboxylic acid substituted calix[8]arene. Different composition ratios of EHO/calix[8]arene have been examined to determine the optimum composition for deposition and gas sensitivity. It has been found that the addition of a calix[8]arene host has a dramatic effect on the half-life of both the response and the recovery. In previous studies, typical t(50) values of 25 s for the response phase of a pure EHO system to NO2 have been obtained. The addition of 60 - 80% of calix[8]arene reduces this to a very low value of 6 s, showing that the calix[8]arene host matrix indeed improves the sensor performance of EHO-containing materials. (C) 2002 Elsevier Science B.V. All rights reserved.