DNA single strands can be applied as templates for the self-assembly of Py≡dU chromophores in H2O with optical properties that are very similar to Py≡dU stacks that are covalently attached to DNA. The chirality, however, of the non-covalent stacks is opposite to that of the covalent stacks.

The chromophores ethynyl pyrene as blue, ethynyl perylene as green and ethynyl Nile red as red emitter were conjugated to the 5-position of 2'-deoxyuridine via an acetylene bridge. Using phosphoramidite chemistry on solid phase labelled DNA duplexes were prepared that bear single chromophore modifications, and binary and ternary combinations of these chromophore modifications. The steady-state and time-resolved fluorescence spectra of all three chromophores were studied in these modified DNA duplexes. An energy-transfer cascade occurs from ethynyl pyrene over ethynyl perylene to ethynyl Nile red and subsequently an electron-transfer cascade in the opposite direction (from ethynyl Nile red to ethynyl perylene or ethynyl pyrene, but not from ethynyl perylene to ethynyl pyrene). The electron-transfer processes finally provide charge separation. The efficiencies by these energy and electron-transfer processes can be tuned by the distances between the chromophores and the sequences. Most importantly, excitation at any wavelength between 350 and 700 nm finally leads to charge separated states which make these DNA samples promising candidates for light-harvesting systems.

Control by conformation: The photophysical interactions and energy transfer between the covalently attached chromophores ethynyl pyrene (Py) and ethynyl nile red (Nr) can be much better realized when modulated with the sterically constrained pyrrolidinyl PNA (shown in green) than with pure DNA.

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