Strain-Induced Stereoselective Formation of Blue-Emitting Cyclostilbenes

We describe the synthesis of two conjugated macrocycles that are formed from the end-to-end linking of stilbenes. We have named these macrocycles cyclo­stilbenes. The two cyclo­stilbene isomers created in this study differ in the configuration of the double bond in their subunits. These macrocycles are formed selectively through a stepwise reductive elimination from a tetra­platinum precursor and subsequent photo­isomerization. Single-crystal X-ray diffraction reveals the formation of channel architectures in the solid state that can be filled with guest molecules. The cyclo­stilbene macrocycles emit blue light with fluorescence quantum yields that are high (>50%) and have photoluminescence lifetimes of ∼0.8–1.5 ns. The breadth and large Stokes shift in fluorescence emission, along with broad excited-state absorption, result from strong electronic–vibronic coupling in the strained structures of the cyclo­stilbenes.