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

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 Zn 2+ , Cu 2+ , Fe 3+ and Al 3+ cation (chloride) evidenced by their CV and 1 H NMR. With a L2 :M (1:2), there are discernable UV–vis spectrum/ 1 H NMR changes in the presence Cu 2+ , Fe 3+ , Al 3+ . Anion plays a key role in the cation binding process as the chromogenic response to Li + , Na + , K + , Ba 2+ 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 t 1/2  ~ 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 E p(II) more negative, while other cations shift E p(II) to positive. L2 is an ion pair acceptor that binds hydroxide and fluoride salt chromogenic.