Supramolecular complexation and photochirogenesis with inherently chiral molecular clip: Enantiodifferentiating photoisomerization of (Z,Z)-1,3-cyclooctadiene and polar photoaddition to 1,1-diphenylpropene

Inherently chiral molecular clip (MC) 2 binds (Z,Z)-1,3-cyclooctadiene (COD) and 1,1-diphenylpropene (DPP) in 4:1:5 THF-MeOH-H₂O solution (at 25°C) with association constants of 8800 and 27000 M^-1, respectively. The thermodynamic parameters obtained from the van't Hoff analysis (ΔH° = -96.4 kJ mol^-1, ΔS° = -239 J mol ^-1 K^-1) reveal that the binding of DPP by MC is strongly driven by the enthalpic gain from hydrophobic and π-π stacking interactions, which is however largely cancelled out by the entropic loss arising from the tight molecular association. Supramolecular photosensitization by MC 2 facilitates the Z-E isomerization of COD to chiral (E,Z)-isomer in a good E/Z ratio of 0.19 and a low ee of 0.7%, but does not appear to work with DPP probably due to the less-efficient electron transfer in the acceptor-donor-acceptor complex of DPP with MC 2.