Mechanistic Interplay between Light Switching and Guest Binding in Photochromic [Pd₂Dithienylethene₄] Coordination Cages

Abstract

-symmetric DTE chromophore quickly converts between energetically degenerate P and M helical conformations. After binding homochiral 1 R-( -) or 1 S-( +) camphor sulfonate ( R-CSA or S-CSA), guest-to-host chirality transfer was observed via a circular dichroism (CD) signal for the cage-centered absorption. Irradiating the R/S-CSA@ o-C host-guest complexes at 313 nm produced configurationally stable "closed" photoisomers, thus locking the induced chirality with an enantiomeric excess close to 25%. This value (corresponding to chiral induction for one out of four ligands), together with DOSY NMR, ion mobility mass spectrometry, and X-ray structure results, shows that closure of the first photoswitch is sufficient to expel the guest from the cavity.