Single-molecule spectroscopy of a dendrimer-based host-guest system

We report on a single-molecule study of a host - guest system that consists of a second-generation polyphenylene dendrimer and the cyanine dye Pinacya nol. The use of single-molecule spectroscopy enables us to obtain more deta iled information on the properties of the host-guest system and can be used to confirm solution data. At low dye to dendrimer ratios the system is pre sent as a one-to-one complex. while for higher ratios an ion-pair system is formed. Changes in the spectral properties of the single molecules are exp lained by differences in local polarisability. The difference of the triple t lifetimes of single free dye molecules and of associated ones is interpre ted as deriving from a larger free volume for the dye molecules in the dend ritic host relative to the rigid polymer matrix.