Single Boryl Isomerization in Silyl-Bridged Photochromic Diboryl Dyes

Silyl-bridged dimers of a ppy-BMes2 (ppy = 2-phenylpyridine, Mes = mesityl) photochrome were found to undergo photochromic switching involving a single boryl unit only. A through-space intramolecular energy transfer was found to be responsible for the single-chromophore isomerization phenomenon and fluorescence quenching. Steric congestion in the diboryl molecules was found to have an impact on photoisomerization quantum efficiency.