A Doubly Alkynylpyrene-Threaded [4]Rotaxane That Exhibits Strong Circularly Polarized Luminescence from the Spatially Restricted Excimer

The Sonogashira coupling of gamma-CD-encapsulated alkynylpyrenes with terphenyl-type stopper molecules gave a doubly alkynylpyrene-threaded [4]rotaxane. The rotaxane showed only excimer emission, with a high fluorescence quantum yield of Phi(f)=0.37, arising from the spatially restricted excimer within the cavity of the gamma-CD. The excimer emission suffered little from self-quenching up to a concentration of 1.5 x 10(-5) M and was circularly polarized with a high g(lum) value of -1.5 x 10(-2). The strong circularly polarized luminescence may result from the two stacked pyrenes existing in the rotaxane in an asymmetrically twisted manner.