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Van, E. M. H. P. Dijk
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article
Synthesis and characterization of long perylenediimide polymer fibers : from bulk to the single-molecule level
Abstract
The synthesis and characterization of perylenediimide polyisocyanides is reported. In addn. to short oligomers, our synthetic approach results in the formation of extremely long, well-defined, and rigid perylenediimide polymers. Ordering and close-packing of the chromophores in these long polymers is guaranteed by attachment to a polyisocyanide backbone with amino acid side chains. Hydrogen bonding interactions between those groups stabilize and rigidify the helical polymer structure. The rodlike nature of the synthesized long perylenediimide pendant polyisocyanides as well as the helical arrangement of the chromophores is demonstrated by means of at. force microscopy. Remarkably, polymer fibers up to 1 mm in length have been visualized, contg. several thousands of perylenediimide mols. CD spectroscopy reveals the chiral organization of the chromophore units in the polymer, whereas absorption and emission measurements prove the occurrence of excited-state interactions between those moieties due to the close packing of the chromophore groups. However, an intricate optical behavior is encountered in bulk as a result of the coexistence of short oligomers and long polymers of perylenediimide, a situation subsequently uncovered by means of single-mol. expts. Individual long helical perylenediimide polyisocyanides exhibit a typical red-shifted fluorescence spectrum, which, together with depolarized emission continuously decreasing in time, demonstrate that fluorescence arises from multiple excimer-like species in the polymer. Upon continuous irradn. of these long polymers, a fast decay in fluorescence lifetime is obsd., a situation explained by photoinduced creation of quenching sites. Radical/ion formation by intramol. electron transfer between close-by perylenediimide moieties is the most probable mechanism for this process. Appropriate control of the electron-transfer process might open the possibility of applying these polymers as perylenediimide-based supramol. nanowires. [on SciFinder (R)]