Alexander Schulz, Rebecca Fröhlich, Ajay Jayachandran, Franziska Schneider, Matthias Stolte, Tobias Brixner, Frank Würthner

• Highlights • A sequential synthetic protocol affords a stacked merocyanine hetero-foldamer • Exciton coupling leads to a band structure for panchromatic light absorption • Ultrafast energy transfer affords the population of a highly emissive lowest state • Fluorescence brightness increases 14-fold for panchromatic light absorption Summary Natural photosystems accomplish panchromatic light absorption by different chromophores that are non-covalently embedded in protein matrices and mostly lack close dye-dye interactions. In this article,Highlights • A sequential synthetic protocol affords a stacked merocyanine hetero-foldamer • Exciton coupling leads to a band structure for panchromatic light absorption • Ultrafast energy transfer affords the population of a highly emissive lowest state • Fluorescence brightness increases 14-fold for panchromatic light absorption Summary Natural photosystems accomplish panchromatic light absorption by different chromophores that are non-covalently embedded in protein matrices and mostly lack close dye-dye interactions. In this article, we introduce a light-harvesting (LH) system established by four different merocyanine dyes that are co-facially stacked by dipole-dipole interactions and a peptide-like backbone in a folded heteromer architecture to afford a panchromatic absorption band consisting of several strongly coupled exciton states. This exciton manifold allows for ultrafast and efficient energy transport in the artificial antenna. Furthermore, due to the tight stacking of the dyes in their folded state, non-radiative processes are slowed down, thereby increasing the lifetime of the excited state and the fluorescence quantum yield from <3% for the individual dyes up to 38% for the folda-heteromer. Together with the panchromatic absorption, this leads to a substantial improvement of the fluorescence brightness upon broadband excitation in comparison with its constituent chromophores.…