Substituent Effect Induces Emission Modulation of Stilbene Photoswitches by Spatial Tuning of the N/B Electronic Constraints.

We present a family of stilbene derivatives (-) ortho-functionalized with an electron donor and acceptor. Their emission was tuned by donor substitutions, dictating charge transfer dependent on the N···B spatial separation. The steric reduction of substituents on N leads to stronger emission responses upon trans-to-cis photoisomerization. Upon further approach, a bistable isomer was photochemically achieved (: R = Me, R = H) with quenched emission, which is ascribed to the pronounced B···N constraint via B ← NH coordination in -.