DNA-Mediated Exciton Coupling and Electron Transfer between Donor and Acceptor Stilbenes Separated by a Variable Number of Base Pairs

Abstract

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 [Deltaepsilon approximately Rda(-2) sin(2theta)]. Pulsed laser excitation of the stilbenediamide results in creation of the acceptor-donor radical ion pair, which decays via charge recombination. The dynamics of charge separation and charge recombination display an exponential distance dependence, similar to that observed previously for systems in which guanine serves as the electron donor. Unlike exciton coupling between the stilbenes, there is no apparent dependence of the charge-transfer rates upon the dihedral angle between donor and acceptor stilbenes. The introduction of a single G-C base pair between the donor and acceptor results in a change in the mechanism for charge separation from single step superexchange to hole hopping.

Electron transfer reactions of rigid, cofacially compressed, π-stacked porphyrin–bridge–quinone systems

“…As underscored by the extensive literature in the area [124][125][126]129,165,[172][173][174][175][176][177][178][179][180][181][182][183][184][185][186][187][189][190][191][192][193][194][195][196][197], the popularity of double-stranded DNA and related nucleobase scaffolds for interrogating issues pertinent to stacked manifold electronic coupling derives largely from their ease of synthesis. Fabrication ofstacked assemblies, in which interactions between cofacially aligned D, Sp, and A moieties differ radically from deoxyribonucleic acid-based systems, is inherently more challenging.…”

“…In the late 1980s, Barton pioneered the use of double-stranded DNA as a template to interrogate electronic coupling through stacked, -cofacial assemblies . Giese [192][193][194][195][196][197], Lewis and Wasielewski [180][181][182][183][184][185][186][187], Schuster [172][173][174][175][176], Meade [177][178][179], Beratan [124][125][126]129], Tanaka [189,190] and Fukui [189][190][191], and Ratner [165,[216][217][218][219][220] have since investigated a wide range of mechanistic issues related to DNA-mediated charge transport. ET assemblies that utilize double-stranded DNA as the Sp separating D from A define model assemblies with which to probe electronic coupling mediated by -cofacial aromatic units.…”

Excited states and energy transfer among DNA bases in double helices

“…10 Others were based on the changes observed in the spectra of steady-state UV absorption and circular dichroïsm recorded for a series of capped duplexes of various lengths. [11][12][13] Both types of studies concluded on delocalization of the excitation over a few bases.…”

Hole Mobility in DNA A Tracts

“…[16,17] Selective excitation of the Sa capping group at 350-355 nm permits observation of the decay of 1 Sa* (both fluorescence and stimulated emission with a 385-nm band maximum), and the formation of Sa À C (575-nm band maximum) and Sd + C (525-nm band maximum). Hole arrival times for 1-4 were estimated from the rise in the band ratio at 525/575 nm.…”