[2]Pseudorotaxane Formation with FRET Based Luminescence Response: Demonstration of Boolean Operations through Self-Sorting on Solid Surface

Binary pseudorotaxane formation between an aza crown derivative as host (<b>H</b>) and two different imidazolium derivatives as guests (<b>G</b>_<b>1</b> and <b>G</b>_<b>2</b>) have been studied in detail by NMR (¹H NMR, 2D NOESY), optical (steady state electronic and emission spectroscopy), and mass spectroscopy. Binding stoichiometry (1:1), association constant for the respective [2]­pseudorotaxane formation (<i>K</i>_a^{<b>H.G</b>_<b>1</b>} = (2.61 ± 0.015) × 10³ M^–1 and <i>K</i>_a^{<b>H.G₂</b>} = (1.27 ± 0.16) × 10³ M^–1), and associated thermodynamic parameters are also evaluated based on isothermal titration calorimetric (ITC) studies. FRET based <i>luminescence ON</i> responses are observed on formation of the binary pseudorotaxane (<b>H.G</b>_<b>1</b> and <b>H.G</b>_<b>2</b>) in a nonpolar medium like dichloromethane. The thermodynamic feasibility of such an energy transfer process is also examined. The higher affinity of <b>H</b> and 18-crown-6 toward K⁺, as compared to those toward <b>G</b>_<b>1</b> or <b>G</b>_<b>2</b>, and the reversibility in the host–guest binding process are utilized in demonstrating the self-sorting phenomena with associated changes in luminescence responses that could be correlated for Boolean operators like YES, INHIBIT, OR, and AND gates