A room temperature phosphorescence encoding [2] rotaxane molecular shuttle

A novel bistable molecular shuttle, composed of a Pt(II) porphyrin-containing dibenzo[24] crown-8 macrocycle threaded onto two different recognition sites (secondary dialkylammonium (NH2+) and 4,4'-bipyridinium (Bpym(2+)) units), and the anthracene (Anth) moiety as one terminal stopper, was synthesized by click chemistry. Its acid-base switchable shuttling could be addressed by both the room temperature phosphorescence (RTP) emission signals of the Pt(II) porphyrin moiety and the fluorescence emission of the Anth unit, as well as their lifetime changes. When the macrocycle was switched to be located on the NH2+ site close to Anth, the Pt(II) porphyrin moiety exhibited strong RTP emission, excited in the Anth band at 370 nm. This was due to the distance-dependent efficient singlet energy transfer between the Anth unit and the porphyrin moiety, followed by intersystem crossing from a singlet to a triplet state in Pt(II) porphyrin, while its RTP emission dramatically decreased when located on the Bpym(2+) site far from the Anth unit. When excited in the porphyrin band at 402 nm, the RTP emission lifetimes changed obviously. This is the first rotaxane-type molecular shuttle whose shuttling has been encoded by RTP signals.