Exciton delocalization, charge transfer, and electronic coupling for singlet excitation energy transfer between stacked nucleobases in DNA: An MS-CASPT2 study

Abstract

Articles you may be interested inFragment transition density method to calculate electronic coupling for excitation energy transfer J. Chem. Phys. 140, 244117 (2014) Exciton delocalization and singlet excitation energy transfer have been systematically studied for the complete set of 16 DNA nucleobase dimers in their ideal, single-strand stacked B-DNA conformation, at the MS-CASPT2 level of theory. The extent of exciton delocalization in the two lowest (π ,π * ) states of the dimers is determined using the symmetrized one-electron transition density matrices between the ground and excited states, and the electronic coupling is calculated using the delocalization measure and the energy splitting between the states [see F. Plasser, A. J. A. Aquino, W. L. Hase, and H. Lischka, J. Phys. Chem. A 116, 11151-11160 (2012)]. The calculated couplings lie between 0.05 eV and 0.14 eV. In the B-DNA conformation, where the interchromophoric distance is 3.38 Å, our couplings deviate significantly from those calculated with the transition charges, showing the importance of orbital overlap components for the couplings in this conformation. The calculation of the couplings is based on a two-state model for exciton delocalization. However, in three stacks with a purine in the 5 position and a pyrimidine in the 3 one (AT, GC, and GT), there is an energetically favored charge transfer state that mixes with the two lowest excited states. In these dimers we have applied a three-state model that considers the two locally excited diabatic states and the charge transfer state. Using the delocalization and charge transfer descriptors, we obtain all couplings between these three states. Our results are important in the context of DNA photophysics, since the calculated couplings can be used to parametrize effective Hamiltonians to model extended DNA stacks. Our calculations also suggest that the 5 -purine-pyrimidine-3 sequence favors the formation of charge transfer excited states.

New tools for the systematic analysis and visualization of electronic excitations. I. Formalism

“…(17) into individual atomic contributions. Formally, one may define the (gross) population number of atom A in state I (20) as the integral of the density over the space belonging to this atom. The net charge of the atom…”

“…10,12 This analysis proved to be helpful, e.g., for studying the structure of excitons in conjugated organic polymers 17 and for quantifying delocalization and charge transfer effects in DNA base stacks. 16,20 Furthermore, the effect of charge resonance interactions on the formation of excimers was highlighted using this approach. 10,61,62 …”

“…10 However, also the potential of this latter methodology has already been exploited by a number of researchers studying organic electronics and photobiology. [16][17][18][19][20] A unified formalism is present through the use of one-particle density matrices (1DM) and transition density matrices, a common ground, which allows for a clear comparison between the different methods and suggests extensions leading to a wide variety of routines for population analysis, as well as, orbital and density plotting, which are provided in this implementation. To our knowledge, a similarly comprehensive analysis toolbox has not been made available so far, let alone in a correlated ab initio framework.…”

Statistical analysis of electronic excitation processes: Spatial location, compactness, charge transfer, and electron-hole correlation

“…In a more general sense, the problem can be traced back to correlation effects between the electron and hole quasi‐particles . A number of strategies to overcome this problem have been introduced by different authors but their application is still quite limited …”

“…The electronic promotion number arising in the attachment/detachment analysis can be used to quantify orbital relaxation . And, finally, the squared norm of the 1TDM, which arises as normalization factor in the aforementioned electron‐hole correlation analysis, serves as a universal measure of single‐excitation character . Furthermore, the different densities discussed above can be subjected to population analyses to divide them into different atomic contributions .…”