Cyclodextrin-Isolated Alkynylpyrenes as UV-Stable and Blue-Light-Emitting Molecules Even in Condensed States.

Encapsulation of highly emissive alkynylpyrenes with permethylated α-cyclodextrin (PM-α-CD) followed by capping reaction yielded alkynylpyrene-based [3]rotaxanes. The [3]rotaxane emitted only blue light of monomeric pyrene under various circumstances such as lipophilic, hydrophilic, and even condensed states and exhibited extremely high stability for UV irradiation. These properties would result because PM-α-CD, like bulletproof glass, protected the alkynylpyrene core from the attack of another excited alkynylpyrene and singlet oxygen generated by the energy transfer from the excited alkynylpyrene.

A doubly alkynylpyrene-threaded [4]rotaxane that exhibits strong circularly polarized luminescence from the spatially restricted excimer.

The Sonogashira coupling of γ-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 Φf =0.37, arising from the spatially restricted excimer within the cavity of the γ-CD. The excimer emission suffered little from self-quenching up to a concentration of 1.5×10(-5) M and was circularly polarized with a high glum  value of -1.5×10(-2) . The strong circularly polarized luminescence may result from the two stacked pyrenes existing in the rotaxane in an asymmetrically twisted manner.