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.