Dynamics of Charge Separation from Second Excited State and Following Charge Recombination in Zinc-Porphyrin–Acceptor Dyads

Abstract

Intramolecular charge separation from the second singlet excited state of directly linked Zn-porphyrin-imide dyads and following charge recombination into the first singlet excited and the ground states has been investigated in the framework of a model incorporating four electronic states (the first and the second singlet excited, the charge separated, and the ground states) as well as their vibrational sublevels. Kinetics of the transitions between these states are described in terms of the stochastic point-transition approach involving reorganization of a number of high frequency vibrational modes. The influence of the model parameters (the number of high frequency vibrational modes, the magnitude of the reorganization energies of the medium and the high frequency intramolecular vibrations, the solvent polarity) on the kinetics of population of the second and first singlet excited states as well as the charge separated state has been investigated. Simulation of the kinetics of the charge separated state population allows quantitative reproducing of the distinctive features of the two-humped kinetic curve observed in the experiment.

Nonstationary Theory of Excited State Charge Transfer Symmetry Breaking Driven by Polar Solvent

“…For the numerical solution of eq , the Brownian simulation method is used, which operates in terms of stochastic trajectories and was successfully used for simulation of electron transfer kinetics. ,− A set of the stochastic trajectories describe the motion of an ensemble of particles on the free energy surface G ( D m ). The free energy G ( D m ) is numerically found by minimization of the free energy functional G int [Ψ, P⃗ ( r⃗ )] with respect to the dissymmetry parameter D using the golden-section search, so far as the domain of the variable D is restricted and belongs the range −1 ≤ D ≤ 1 as well as the G int [Ψ, P⃗ ( r⃗ )] has only one minimum in this domain for a given value of D m .…”

Crystal structure of 4,4′-diethynylbiphenyl

“…Donor-acceptor (D-A) dyads with the innate ability to generate long-lived charge separation in their excited states have elicited a great deal of current interest. Their applications cover fields ranging from artificial photosynthesis to solar cell technology (Rogozina et al, 2013;Fukuzumi et al, 2014). We have produced a variety of such dyads based on ferrocene as the donor and with a variety of acceptors (see for example: Flood et al, 2007;Cuffe et al, 2005;McAdam et al, 2003).…”

The Efficiency of Photoinduced Intramolecular Charge Separation from the Second Excited State: What Factors Can Control It?

“…77,81 For CS from the second excited state in Zn(II)-porphyrin covalently linked to naphthaleneimide and amino naphthalene diimide dyads, E rv was equal to 0.3 and 0.42 eV, respectively. 28,82 In addition, the methods of modern quantum chemistry make it possible to estimate the reorganization energy of intramolecular vibrations even for large molecules. 83−85 These estimations indicate that the energy efficiency of real dyads is expected to be limited by the red and magenta lines in Figure 9.…”

“…Although photochemistry of the first excited state has been investigated rather extensively, ,, experimental and numerical studies of photoinduced CT in higher excited states are still rare. On the other hand, the mechanisms of charge separation from LES2 and LES1 are known to differ from each other in many aspects, − so the methods of enhancing the CS efficiency in these processes can also be different. A general scheme of electronic transitions upon the LES2 excitation is shown in Figure .…”