Photoisomerization of Pt ^II Complexes Containing Two Different Photochromic Chromophores: Boron Chromophore versus Dithienylethene Chromophore

In order to examine competitive photoisomerization, a series of novel photochromic Pt ^II molecules that contain both dithienylethene (DTE) and B(ppy)Mes ₂ units (ppy=2-phenylpyridine, Mes=mesityl) were successfully synthesized and fully structurally characterized. Their photochromic properties were examined by UV/Vis, emission and NMR spectroscopy. It was found that the DTE unit in all three compounds is the preferred photoisomerization site, exhibiting reversible photochromism with irradiation. The B(ppy)Mes ₂ unit does not undergo photoisomerization in these molecules, but likely enhances the photoisomerization quantum efficiency of the DTE moiety through the antenna effect. Extended irradiation with UV light leads to the rearrangement of the ring-closed isomers of DTE. TD-DFT computational studies indicate that the DTE photocyclization proceeds via a triplet pathway through an efficient energy transfer process.