Synthetic β-Cyclodextrin Dimers for Squaraine Binding: Effect of Host Architecture on Photophysical Properties, Aggregate Formation and Chemical Reactivity

Reported herein is the synthesis and application of three novel β-cyclodextrin dimer hosts for the complexation of near infrared (NIR) squaraine dyes in aqueous solution. A series of eight different N-substituted N-methyl anilino squaraine dyes with variable terminal groups are investigated, with an optimal n-hexyl-substituted squaraine guest demonstrating binding constants orders of magnitude higher than the other squaraine–host combinations and comparable to literature-reported systems. Moreover, hydrophobic complexation of the squaraine dyes with the β-cyclodextrin dimer hosts causes drastic changes in the squaraine's photophysical properties, propensity for aggregation and susceptibility to hydrolytic decay.