Electron Hopping among Cofacially Stacked Perylenediimides Assembled by Using DNA Hairpins

Abstract

The self-assembly of redox-active molecules into ordered arrays capable of rapid, long-distance charge transport is important for the development of functional nanomaterials for organic electronics. In this regard, DNA shows great promise as a structural scaffold for the helical arrangement of chromophores and other (semi)conducting materials. [1][2][3] Base substitutions and modifications, sugar modifications, and noncovalent interactions have all been used for the construction of such DNA-based structures. Perylenediimides (PDIs), which have the advantages of strong absorptivity, high fluorescence quantum yields, high photochemical and thermal stability, strong hydrophobic p-p stacking interactions, and semiconducting properties, have been incorporated in a variety of structures. [4][5][6][7][8][9][10][11][12][13][14][15][16] Recently, Wagner and Wagenknecht [10] reported the preparation of a PDI derivative, P (Figure 1), which is readily incorporated into an oligonucleotide and serves as a base-pair surrogate when located opposite an abasic site in a duplex structure. The incorporation of P in opposite complementary oligonucleotides has been shown to result in the formation of stable duplexes in which the P units are located in a zipperlike fashion within the hydrophobic interior of the resulting duplex. [5,17] The stacking of P units within the duplex resulted in an excimer-like state following photoexcitation. [16] We report herein the results of our investigation of intramolecular electron hopping within a series of synthetic DNA hairpins 1-4 (Figure 1). These hairpins possess compact 3'-CCA loop regions connecting poly(T)-poly(A) stems containing a single P moiety located opposite an abasic site (1), two P moieties located opposite abasic sites and attached either to the same strand (in 2 s) or to opposite strands (in 2 o), or three or four P moieties positioned adjacent to one another but on opposite strands in a zipperlike fashion (in 3 and 4). The EPR spectra of the singly reduced duplexes were consistent with electron hopping between two sites in both dimers (the hairpins containing two P moieties) and the trimer 3, and among three sites in the tetramer 4. Herein, we discuss the origin and implications of partial electron sharing.Oligonucleotides containing P were synthesized by the method of Wagner and Wagenknecht; [10] the CCA linker in hairpins 1-4 has been employed previously in the synthesis of stable minihairpins. [13,17,18] The characterization of 1-4, including mass spectrometry and circular dichroism (CD), is described in the Supporting Information.An intensity reversal was observed in the UV/Vis absorption spectra for the 0!0 and 0!1 transitions in 2-4 with respect to those of 1 (Figure 2). This result indicates that the p-stacked P chromophores are exciton-coupled. [19][20][21] Moreover, the A 0!0 /A 0!1 ratio for the vibronic bands decreased as the number of P units increased, and there was a notable difference between dimers 2 s and 2 o, presumably as a result of the conformational changes...

DNA‐Templated Synthesis of Perylenediimide Stacks Utilizing Abasic Sites as Binding Pockets and Reactive Sites

“…The absorption in the visible region attributable to the PDI chromophore showed a spectral change from the PDI monomer to the exciton‐coupled spectra, indicating the formation of stacked PDI chromophores within the DNA (Table ). These spectral changes, with apparent blue shifts ( A 546 / A 507 ), are consistent with previous reports relating to PDI assembly . The A 546 / A 507 value for P1 was closely consistent with that of PDI monomer in the noncovalent PDI/DNA complex .…”

Rapid Electron Transfer of Stacked Heterodimers of Perylene Diimide Derivatives in a DNA Duplex

“…In addition, after the decay of 1 PH*, PH .− was not observed, which was inconsistent with the observation for PH/Sp (Figure b). Based on the reduction potential of 1 PH* ( E red =2.0 V calculated from the reduction potential ( E red =0.34 V vs. a normal hydrogen electrode (NHE)), singlet excitation energy ( E s =2.3 eV), and oxidation potential of PN ( E ox =0.8 V vs. NHE), electron transfer from PN to 1 PH* is expected to occur with a driving force of about −1.2 eV . Therefore, the rapid decay of 1 PH* without the appearance of the transient absorption of PH .− indicates that the electron‐transfer reaction between 1 PH and PN, and back‐electron transfer in PH/PN, takes place within a few picoseconds; this originates from the favorable driving force and face‐to‐face arrangement of PH and PN (Figure c).…”

Photoresponsive Electrodes Modified with DNA Duplexes Possessing a Porphyrin Dimer

“…As shown in Figure a, after photoexcitation, the initial electron‐transfer reaction between the Por in the excited state and MV 2+ occurs to generate the Por .+ and MV .+ pair. When the Por molecule exists near Por .+ , a positive charge shift (hole transfer) could occur to prevent or slow down the charge recombination reaction, resulting in enhancement of the PC intensity . Exciton migration or delocalization between two Por molecules also needs to be considered.…”