Amplified photomodulation of a bis(dithienylethene)-substituted phosphine.

Phosphine ligands play a crucial role in homogeneous catalysis, allowing fine-tuning of the catalytic activity of various metals by modifying their structure. An ultimate challenge in this field is to reach controlled modulation of catalysis in situ, for which the development of phosphines capable of photoswitching between states with differential electronic properties has been proposed. To magnify this light-induced behavior, in this work we describe a novel phosphine ligand incorporating two dithienylethene photoswitchable moieties tethered to the same phosphorus atom. Double photoisomerization was observed for this ligand, which remains unhindered upon gold(I) complexation. As a result, the preparation of a fully ring-closed phosphine isomer was accomplished, for which amplified variation of phosphorus electron density was verified both experimentally and by computational calculations. Accordingly, the presented molecular design based on multiphotochromic phosphines could open new ways for preparing enhanced photoswitchable catalytic systems.