Showing papers by "Wanhua Wu published in 2018"

Supramolecular Photochirogenesis Driven by Higher-Order Complexation: Enantiodifferentiating Photocyclodimerization of 2-Anthracenecarboxylate to Slipped Cyclodimers via a 2:2 Complex with β-Cyclodextrin.

Abstract: Chiral slipped 5,8:9′,10′-cyclodimers were preferentially produced over classical 9,10:9′,10′-cyclodimers upon supramolecular photocyclodimerization of 2-anthracenecarboxylate (AC) mediated by β-cyclodextrin (β-CD). This photochirogenic route to the slipped cyclodimers, exclusively head-to-tail (HT) and highly enantioselective, has long been overlooked in foregoing studies but is dominant in reality and is absolutely supramolecularly activated by 2:2 complexation of AC with β-CD. The intricate structural and photophysical aspects of this higher-order complexation-triggered process have been comprehensively elucidated, while the absolute configurations of the slipped cyclodimers have been unambiguously assigned by comparing the experimental and theoretical circular dichroism spectra. In the 2:2 complex, two ACs packed in a dual β-CD capsule are not fully overlapped with each other but are only partially stacked in a slipped anti- or syn-HT manner. Hence, they do not spontaneously cyclodimerize upon photoex...

Supramolecular Assembly‐Improved Triplet–Triplet Annihilation Upconversion in Aqueous Solution

Abstract: Water-soluble 9,10-diphenylanthracene-modified γ-cyclodextrin derivatives A1 and A2, in which the γ-cyclodextrin unit serves as a molecular host for a binding sensitizer, and the 9,10-diphenylanthracene moiety plays a role as an emitter/annihilator, were synthesized to investigate the supramolecular triplet-triplet annihilation (TTA) upconversion in aqueous solution. Both A1 and A2 readily aggregate and form nanoscale assemblies in water as a combined result of host-guest complexation and π-π stacking among the 9,10-diphenylanthracenes. The aggregation behavior of the supramolecular emitters was fully characterized by using a diversity of methods, including dynamic light scattering (DLS), SEM, NMR, fluorescence, and circular dichroism studies. Fluorescence spectroscopic analysis reveals that the emitters have high fluorescence quantum yields in water (82 and 90 % for A1 and A2, respectively), thus demonstrating that aggregation does not quench the fluorescence. By using a coordinated ruthenium sensitizer, a high TTA upconversion quantum yield of up to 6.9 % was observed for this supramolecular TTA system, which is significantly higher than the value (<0.5 %) obtained with nonassembled emitters in organic solvent and in contrast to the fact that TTA upconversion emission in aqueous solution is usually low or negligible. We ascribe the strong TTA upconversion emission in the present supramolecular assembly system to an efficient TTA process, which is facilitated along the stacked emitters by triplet energy migration and improved triplet-triplet energy transfer through host-guest complexation.