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

We present a family of stilbene derivatives (1-4) 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 (4: R1 = Me, R2 = H) with quenched emission, which is ascribed to the pronounced B···N constraint via B ← NH coordination in cis-4.