The present invention relates generally to the transfer of non-fluorescent energy between donor and acceptor moieties. In certain embodiments, the invention provides biomolecules that include substantially non-fluorescent donor moieties. Processes involving these donor moieties typically entail reduced background fluorescence relative to applications that involve conventional fluorescent donor moieties. In addition to reaction mixtures and methods that include the use of these biomolecules, the invention also provides related kits and systems.