Synthesis, characterization, and chemical sensitivity of self-assembled bilayers composed of polydiacetylenes and calix[4]arenes chemically modified on the upper rim

We report the synthesis, characterization, and sensor-related chemistry of self-assembled polydiacetylene (PDA)/calix[4]arene-X (CA[4]-X; X = -H, phenylazo, and -dibenzylamino) bilayers on Au surfaces. Surface infrared spectroscopy indicates that acid chloride-terminated PDA self-assembled monolayers (SAMs) react with hydroxyl groups present on the lower rim of the calixarenes to yield ester-linked bilayers. Nanogravimetric titrations of unreacted PDA acid groups with n-butylamine indicate that the three CA[4]-X derivatives cover an average of 69% of the PDA surface. The mass titration serves a secondary purpose by passivating voids between calixarenes with n-butylamine. The response of the bilayers to four aromatic analytes: anisole, benzene, chlorobenzene, and toluene, was determined using surface acoustic wave (SAW) mass balances. The results indicate that the upper-rim functional groups of CA[4]-X have a significant effect on the sensitivity and selectivity of the bilayer toward the vapor-phase analytes. Increased sensitivity and selectivity are observed for the CA[4]-phenylazo and CA[4]-dibenzylamino bilayers relative to CA[4]-H or a simple methyl-terminated n-alkylthiol SAM. We interpret these results in terms of the large -phenylazo and -dibenzylamino functional groups, which enlarge the calixarene cavities and enhance their ability to interact with aromatic analytes by pi-pi stacking interactions.