pH-Controlled enantioselectivity switching of irregular photodimers in photocyclodimerization of 2-anthracenecarboxylic acid mediated with β-cyclodextrin derivatives

Abstract

A series of modified β-cyclodextrins (CDx's) with a mono/bis-quinoline tether was synthesized and used as chirogenic supramolecular hosts for mediating the enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylic acid (AC) at various pH. Based on the enantiodifferentiating results of the native CDx's, the modified derivatives significantly enhanced the chemical and optical yields of irregular photodimers 5 and 6. Interestingly, the flexible bis-quinoline tethered CDx derivative 10 and its N-methylated homolog 11 inverted the stereochemical outcome of syn-head-to-tail dimer 6 from 48.7 to −68.2% and 64.2 to −81.2%, respectively, upon changing the solution pH from 1 and 9. Binding models before and after pK_a of the complex were proposed based on the photodimerization results, various spectroscopic studies and computational simulation.