Relationship between the photoinduced electron transfer and binding modes of a pyrene–porphyrin dyad to DNA

Abstract

The binding modes of a pyrene-porphyrin dyad, (1-pyrenyl)-tris(N-methyl-p-pyridino)porphyrin (PyTMpyP), to DNA and its photophysical properties have been investigated using various spectroscopic techniques. The circular dichroism (CD) spectrum of PyTMpyP bound to DNA (PyTMpyP-DNA) showed one negative and two positive bands in the Soret region. The CD signal in the pyrene absorption region was positive. The shape of the CD spectrum does not support an intercalative binding mode of TMpyP, which would typically afford a negative CD band in the absence of the pyrene moiety. Linear dichroism (LD) experiments revealed a very small signal in the Soret region, which also challenges the intercalation of TMpyP into DNA. Upon excitation of the pyrene moiety, the emission intensity of porphyrin in aqueous solution was quenched due to a photoinduced electron transfer (PET) process between the pyrenyl and porphyrin moieties. On the other hand, the emission of porphyrin was markedly enhanced upon binding to DNA, as the PET process from the excited pyrene moiety to TMpyP was suppressed when bound to DNA. The PET process occurs in the timescale of 65 ps, and could be detected by femtosecond transient absorption spectroscopic methods. Two fluorescence decay times were observed for PyTMpyP in aqueous solution (0.78 and 4.8 ns). Both decay times increased upon binding to DNA owing to environment and/or conformational changes in PyTMpyP. The driving force (ΔG) of the PET process was evaluated under conditions of minor and major groove binding. The PET process and photophysical properties of the PyTMpyP dyad were concluded to be influenced by the binding mode.

Pomegranate‐Inspired Cathodes Mitigate the Mismatch Between Carrier Transport and High Loading for Aqueous Zinc‐Ion Batteries

“…[ 40 ] The faint signal of D + D' at 2970 cm −1 corresponds to the combination mode of the D and D' modes. The confirmation of I D / I G >1 and I 2D / I G <1 indicates the existence of vacancy‐type defects, [ 41 ] a finding consistent with the observation in TEM images. In addition, the FTIR spectra of V 2 O 5 and V 2 O 5 @LIG indicate a redshift of the peaks due to the strong interaction of LIG with V 2 O 5 (Figure S9, Supporting Information).…”

Fully Conjugated Pyrene–BODIPY and Pyrene–BODIPY–Ferrocene Dyads and Triads: Synthesis, Characterization, and Selective Noncovalent Interactions with Nanocarbon Materials

“…Design of new chromophores that are capable of harvesting sunlight in the low-energy visible and near-infrared (NIR) spectral envelopes attracted a lot of attention in recent decades because of the potential use of such systems in organic- and dye-sensitized solar cells. − In addition, the ability to facilitate relatively strong noncovalent interactions between such chromophores and nanocarbon-based electron-accepting materials (fullerenes, nanotubes, and graphene) is thought to be advantageous in the processing of high-efficiency organic bulk heterojunction solar cells. − To achieve this goal, many porphyrins, − subphthalocyanines, − and boron-dipyrromethenes (BODIPYs) were functionalized with a variety of electron-donating groups that improve donor–acceptor (D–A) interactions between extended π-systems. Alternatively, the introduction of the polyaromatic fragments that are either conjugated or not conjugated into chromophores’ π-system can also improve noncovalent interactions in these D–A assemblies. − Covalently bound pyrene was shown to facilitate noncovalent interactions with carbon nanotubes and graphene. − It has also been shown that when pyrene fragments are decoupled from the chromophores’ π-system, this extended aromatic group can facilitate an unwanted pyrene-to-chromophore electron-transfer process as well as the formation of a chromophore-centered triplet state. − We have recently demonstrat...…”

Photoinduced Electron Transfer between DNA and Water-Soluble Porphyrins

“…Within this framework, the rate constants for charge separation and recombination may be expressed as where where ℏ = h /2π ( h is Planck’s constant), k B is the Boltzmann constant, T is the temperature (296 K), H DA is the electronic coupling matrix element, S c is the Huang–Rhys factor, Δ G is the free-energy change, λ i is the nuclear reorganization energy, and ⟨ω c ⟩ is the average high-frequency vibrational frequency. A value of ℏ⟨ω c ⟩ = 1500 cm –1 could be assumed for ET processes involving aromatic molecules. , λ s is the solvent reorganization energy, which is expressed as where ε 0 is the vacuum permittivity, r D (3.0 Å for guanine) and r A (9.2 Å for porphyrin) are the ionic radii of the donor and acceptor, respectively, r DA (= r D + r A ) is the donor–acceptor separation, n (=1.332) is the solvent refractive index, and ε s (=81) is the static dielectric constant of the solvent. − Therefore, the value of λ s has been estimated to be ∼1.10 eV. The values of λ i and H DA can be estimated as ∼0.37 eV and ∼193.5 cm–1, respectively, according to formula 1 by using the experimental results of k b,exp (=1/τ G , see Table ) data of H 2 TMPyP-dGMP and PdTMPyP-dGMP, which are consistent with the earlier reports. ,, Then, the dependence of k values on the driving force (−Δ G ) can be displayed in Figure .…”