Abstract
Exciton coupling between two or more chromophores
in a specific environment is a key mechanism
associated with color tuning and modulation of absorption
energies. This concept is well exemplified by natural photosynthetic
proteins, and can also be achieved in synthetic
nucleic acid nanostructures. Here we report the coupling of
barbituric acid merocyanine (BAM) nucleoside analogues
and show that exciton coupling can be tuned by the double
helix conformation. BAM is a nucleobase mimic that was
incorporated in the phosphodiester backbone of RNA, DNA
and GNA oligonucleotides. Duplexes with different backbone
constitutions and geometries afforded different mutual dye
arrangements, leading to distinct optical signatures due to
competing modes of chromophore organization via electrostatic,
dipolar, π–π-stacking and hydrogen-bonding interactions.
The realized supramolecular motifs include hydrogenbonded
BAM–adenine base pairs and antiparallel as well as
rotationally stacked BAM dimer aggregates with distinct
absorption, CD and fluorescence properties.
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