Electronic Couplings for Singlet Fission Processes Based on the Fragment Particle-Hole Densities

Abstract

A new diabatization scheme is proposed to calculate the electronic couplings for the singlet fission process in multichromophoric systems. In this approach, a robust descriptor that treats single and multiple excitations on an equal footing is adopted to quantify the localization degree of the particle and hole densities of the electronic states. By maximally localizing the particles and holes in terms of predefined molecular fragments, quasi-diabatic states with well-defined characters (locally excited, charge transfer, correlated triplet pair, etc.) can be automatically constructed as the linear combinations of the adiabatic ones, and the electronic couplings can be directly obtained. This approach is very general in that it applies to electronic states with various spin multiplicities and can be combined with various kinds of preliminary electronic structure calculations. Due to the high numerical efficiency, it is able to manipulate more than 100 electronic states in diabatization. The applications to the tetracene dimer and trimer reveal that high-lying multiply excited charge transfer states have significant influences on both the formation and separation of the correlated triplet pair and can even enlarge the coupling for the latter process by 1 order of magnitude.

Identification of the interchromophore interaction in the electronic absorption and circular dichroism spectra of bis-phenanthrenes

“…24,38–41 Within the framework of diabatization schemes, finding the diabatic states is equivalent to constructing an optimal adiabatic-to-diabatic (ATD) transformation matrix. Here we adopt our newly developed diabatization scheme called the fragment particle-hole density (FPHD) method 42,43 to obtain the corresponding state energies and couplings. The central idea of FPHD is to search for orthonormal electronic states that maximally localize electron and hole densities in terms of predefined molecular fragments.…”

“…24 Green et al also adopted a diabatization scheme to find the diabatic states, which starts with the TDDFT calculation to the adiabatic electronic states and construction of the ATD transformation matrix through calculation of the overlapping of the reference states of the fragments with the adiabatic states. 38 Our FPHD schemes 42,43 maximally localize the particles and holes in terms of predefined molecular fragments, in the end the quasi-diabatic states with well-defined characters can be automatically constructed and the couplings between the diabatic states can be directly obtained. They don't require the reference states of the fragments.…”

Singlet Fission in Diphenylhexatriene Amide Derivatives: Effects of Intermolecular Hydrogen Bonds in Crystals

“…In recent years, many experimental and theoretical studies have been devoted to achieving a deep understanding of the dynamics of SF. − There are three possible electronic mechanisms for the formation of (TT): ,,,, (i) direct internal conversion from S* to (TT), (ii) SF mediated by charge transfer (CT) states [CT states as virtual states assisting the formation of (TT) in a superexchange mechanism], or (iii) sequential two one-electron transfer steps with the CT state as a real intermediate effectively populated before the generation of (TT) . If the coupling of CT states with S* and (TT) is significant and the energy difference between S*/(TT) and CT states is considerably small, then the transition is mediated by CT states.…”