DNA-mediated exciton coupling and electron transfer between donor and acceptor stilbenes separated by a variable number of base pairs.

The synthesis, steady-state spectroscopy, and transient absorption spectroscopy of DNA conjugates possessing both stilbene electron donor and electron acceptor chromophores are described. These conjugates are proposed to form nicked DNA dumbbell structures in which a stilbenedicarboxamide acceptor and stilbenediether donor are separated by variable numbers of A−T or G−C base pairs. The nick is located either adjacent to one of the chromophores or between two of the bases. Thermal dissociation profiles indicate that stable structures are formed possessing as few as two A−T base pairs. Circular dichroism (CD) spectra in the base pair region are characteristic of B-DNA duplex structures, whereas CD spectra at longer wavelengths display two bands attributed to exciton coupling between the two stilbenes. The sign and intensity of these bands are dependent upon both the distance between the chromophores and the dihedral angle between their transition dipoles [Δe ≈ Rda-2 sin(2θ)]. Pulsed laser excitation of the ...