Synthesis and Photochemical Properties of Stilbenophanes Tethered by Silyl Chains. Control of (2π + 2π) Photocycloaddition, Cis−Trans Photoisomerization, and Photocyclization

Novel macrocyclic and medium-size stilbenophanes tethered by silyl chains were synthesized, and
their photochemical and photophysical properties were examined. Direct photoirradiation of
macrocyclic stilbenophanes gave intramolecular photocycloadducts stereoselectively, and the
efficiency increased with decreasing distance between the two stilbene units. The triplet-sensitized
photoreaction of stilbenophanes caused cis−trans photoisomerization. Photoreactions of cis-fixed
stilbenophanes under an oxygen atmosphere selectively gave phenanthrenophanes. Fluorescence
quantum yields increased with the introduction of silyl substituents, and hence those of silyl-tethered
stilbenophanes were larger than that of unsubstituted trans-stilbene. Intramolecular excimer
emission was observed when the distances between two stilbene units in the stilbenophanes were
sufficiently small.