Efficient energy transfer from pyrene to perylene assembled inside DNA duplex

Pyrene (donor) and perylene (acceptor) were assembled in a DNA duplex to increase the apparent Stokes' shift of perylene. Multiple donors were introduced in the vicinity of acceptors via D-threoninol and natural base pairs were inserted between donors and acceptors in order to suppress undesired interactions between them. When two pyrene moieties were located in proximity to one perylene with one base pair inserted between them, efficient FRET occurred within the duplex. Thus, strong emission at 495 nm was observed from perylene when excited at 345 nm where pyrene has its absorption. The apparent Stokes' shift became as large as 115 nm with a high FRET efficiency (Phi>1). However, the introduction of more than two pyrenes did not enhance the fluorescence intensity of perylene, due to the short Förster radius (R(0)) of the donor pyrene.