Multimode binding and stimuli responsive displacement of acridine orange dye complexed withp-sulfonatocalix[4/6]arene macrocycles

Interaction of acridine orange (AOH(+)) dye with water soluble anionicp-sulfonatocalix[n]arene (SCXn) hosts, SCX4 and SCX6, having different cavity dimensions, has been investigated using multispectroscopic techniques. Intriguing modulation in the photophysical properties of AOH(+)upon interaction with SCXnhosts indicate the formation of different host-guest complexes at different regions of the host concentrations. At lower host concentrations, AOH(+)undergoes SCXnassisted aggregation, causing a drastic reduction in fluorescence intensity. At higher host concentrations, aggregated-AOH(+)-SCXncomplexes disintegrate and monomeric-AOH(+)-SCXnexo and inclusion complexes are eventually formed, leading to a huge fluorescence enhancement finally. Observed effects are more pronounced with SCX6 as compared to SCX4 host. Time-resolved fluorescence studies indicate that at very high host concentrations, there is also a diffusion-controlled dynamic quenching for both monomeric-AOH(+)-SCXnexo and inclusion complexes, caused by the free SCXnpresent in the solution, a phenomenon not reported before for such host-guest systems. The aggregated-AOH(+)-SCXncomplexes at lower host concentration were employed to investigate displacement study using an antiviral drug, 1-adamantanamine (AD) and a neurotransmitter, acetylcholine (AcCh), as the competitive binders cum external stimuli, which resulted in a drastic recovery of the fluorescence reduced initially due to aggregation process. Though both the AOH(+)-SCXnsystems act as efficient supramolecular assemblies in sensing AD and AcCh as the analytes through fluorescence OFF-ON mechanism, the effect is more pronounced for AOH(+)-SCX4 system as compared to AOH(+)-SCX6. SCXninduced interesting modulation in the photophysical properties of AOH(+)and the stimulus responsive dye displacement observed for aggregated-AOH(+)-SCXnsystems can expectedly find applications in fluorescence OFF-ON sensing, supramolecular functional materials and similar others.