Generating extended foldamer dye stacks and unravelling their evolving exciton dynamics

In biomacromolecules, many amino acids or nucleotides are needed to obtain defined secondary structures and concomitant advanced functionalities. However, when researchers generate synthetic model analogues composed of dyes to predict the (photo-)functional properties of the respective solid-state aggregates they often use dimer models. Here we introduce a foldamer series of closely π-stacked dyes from dimer to 14-mer, obtained by an iterative block-based coupling protocol, that enable the study of oligomer-length effects on their photophysical properties. Spectroscopic techniques identify a distinct change of fluorescence properties at around four to six dye units-affording narrowed fluorescence bands and an increase of the total quantum yield from 47% for the dimer up to 75% for the 14-mer-that is accompanied by the development of a multiexciton state. These results highlight the limitation of the dimer model and motivate future research on well-defined π-stacked foldamers, both as models for solid-state materials and as supramolecular wires for future electronic and photonic applications.