Influence of Cavity Depth on the Responses of SPR Sensors Coated with Self-Assembled Monolayers of Cavitands

Cavitands are synthetic organic compounds with enforced cavities of molecular dimensions. Cavitand Self-assembled Monolayers are shown to be highly responsive materials for SPR based chemical vapor sensing. The SAM approach permits an unambiguous comparison of the influence of cavity depth and synergistic interactions between cavitand and guest molecule. This eliminates the possibility of response biases arising from differences in sensing layer morphology. Consistent with earlier results on spin coated cavitands, aromatic vapors are selectively complexed within cavitand 3 (quinoxaline-bridged cavitand) and show lesser affinity for cavitand 2 (pyrazine-bridged cavitand) and cavitand 1 (methylene-bridged cavitand) owing to their smaller cavity depths. Cavitand 1, with its meniscus shaped pi basic cavity, selectively interacts only with small molecules with acidic methyl groups such as nitromethane and acetonitrile. Modeling results corroborate the experimental data and show that increased van der Waals interactions within cavitand 3 are responsible for the higher selectivity towards aromatic vapors.