A Computational Approach to Electronic Coupling in Molecular Dyads

This work presents a computational study on the electronic coupling element for excitation energy transfer (EET) in donor-acceptor dyads, focusing on systems composed of an anthracene donor and a BODIPY acceptor. For this purpose, we use the excited state orbitals for the donor and the ground state orbitals for the acceptor molecule. A custom-built subroutine calculates the coupling element by constructing a 'reduced density matrix' from the excited donor's hole and particle states. This 'reduced matrix' is then used to solve the Poisson equation, generating Coulomb potential. This potential is subsequently "sandwiched" with the basis functions and finally multiplied by the reduced density matrix corresponding to the acceptor. Applying the methodology to a series of anthracene-BODIPY dyads yielded more promising results which showed good agreement with multi-reference calculations. This study compared five distinct systems, each analyzed with and without a linker, totaling nine unique cases. The calculated coupling elements for the systems with a linker showed good agreement with expected trends, while the non-linker systems exhibited more rapid and significant decrease in coupling with increasing separation. These findings suggest that the linker plays a crucial role in maintaining electronic communication between the donor and acceptor.