Polyphenylene dendrimers with perylene diimide as a luminescent core

A novel synthesis is presented of a fourfold ethynyl-substituted perylene diimide dye 4, which acts as a core molecule for the buildup of polyphenylene dendrimers. Around the luminescent core 4, a first-generation (5), a second-generation (6), and a third-generation (7) polyphenylene dendritic environment consisting of pentaphenylbenzene building blocks are constructed. The dendrimers 5 and 6 are synthesized by an exclusively divergent route, whereas for 7, a combination of a divergent and convergent approaches is applied. Absorption and emission spectra of 5-7 in different solvents and in a film have been measured and compared to a nondendronized model compound 13. In solution, the internal chromophore is scarcely influenced by the dendritic scaffold; however, in the solid state, aggregation of the perylene diimide is prevented very effectively by the four rigid dendrons. Additionally, fluorescence quantum yields in solution have been determined for 5-7 and 13; they decrease as the number of generation increases.

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 Pinacyanol. The use of single-molecule spectroscopy enables us to obtain more detailed 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 present 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 explained by differences in local polarisability. The difference of the triplet lifetimes of single free dye molecules and of associated ones is interpreted as deriving from a larger free volume for the dye molecules in the dendritic host relative to the rigid polymer matrix.

Polyphenylene dendrimers with different fluorescent chromophores asymmetrically distributed at the periphery

A new synthetic approach leading to asymmetrically substituted polyphenylene dendrimers is presented. Following this method, polyphenylene dendrimers decorated with an increasing number of chromophores at the periphery have been obtained up to the second generation. Especially the synthesis of a polyphenylene dendrimer bearing three donor chromophores and one acceptor chromophore has been realized. Intramolecular energy transfer within this molecule is demonstrated by applying absorption and fluorescence measurements.

Intramolecular energy hopping and energy trapping in polyphenylene dendrimers with multiple peryleneimide donor chromophores and a terryleneimide acceptor trap chromophore

Intramolecular Förster-type excitation energy transfer (FRET) processes in a series of first-generation polyphenylene dendrimers substituted with spatially well-separated peryleneimide chromophores and a terryleneimide energy-trapping chromophore at the rim were investigated by steady-state and time-resolved fluorescence spectroscopy. Energy-hopping processes among the peryleneimide chromophores are revealed by anisotropy decay times of 50--80 ps consistent with a FRET rate constant of k(hopp) = 4.6 ns(-1). If a terryleneimide chromophore is present at the rim of the dendrimer together with three peryleneimide chromophores, more than 95% of the energy harvested by the peryleneimide chromophores is transferred and trapped in the terryleneimide. The two decay times (tau(1) = 52 ps and tau(2) = 175 ps) found for the peryleneimide emission band are recovered as rise times at the terryleneimide emission band proving that the energy trapping of peryleneimide excitation energy by the terryleneimide acceptor occurs via two different, efficient pathways. Molecular- modeling-based structures tentatively indicate that the rotation of the terryleneimide acceptor group can lead to a much smaller distance to a single donor chromophore, which could explain the occurrence of two energy-trapping rate constants. All energy-transfer processes are quantitatively describable with Förster energy transfer theory, and the influence of the dipole orientation factor in the Förster equation is discussed.