Anthraquinone functionalized pseudocalixarene for high lithium loading and chromogenic ion-pair recognition in DMSO

Abstract The [2 + 2] condensation between 1,8-dihydroxyanthraquinone diester and 1,3-diamino-2-propanol in ethanol affords pseudocalixarene macrocyclic L2 in high yield. Heating L2 to 200 °C in DMSO can generate much smaller [1 + 1] macrocycle L1. Crystal structure of L1 shows that all non-hydrogen atoms are coplanar except one carbon from 1,3-diamino-2-propanol. L1 is quite inert, but L2 can interact with alkaline, alkaline-earth, as well as Zn2+, Cu2+, Fe3+ and Al3+ cation (chloride) evidenced by their CV and 1H NMR. With a L2:M (1:2), there are discernable UV–vis spectrum/1H NMR changes in the presence Cu2+, Fe3+, Al3+. Anion plays a key role in the cation binding process as the chromogenic response to Li+, Na+, K+, Ba2+ and TBA+ hydroxide. L2 forms 1:1 complex with TBAOH and 2:3 complex with NaOH, KOH, Ba(OH)2 in DMSO. L2 reacts with LiOH in 1:4 stoichiometric and is one of the highest lithium loading ligand. The reaction is second-order with t1/2 ~ 30 min for 0.25 mM L2 in the presence of 4.0 eq. LiOH. Besides hydroxide, L2 can interact with TBAF to form 1:1 host–guest complexes evidenced by their color and NMR change. With bulky cation, TBAOH shifts Ep(II) more negative, while other cations shift Ep(II) to positive. L2 is an ion pair acceptor that binds hydroxide and fluoride salt chromogenic.