Quantum Dynamics Simulations of Excited State Energy Transfer in a Zinc–Free-Base Porphyrin Dyad

Rational
design of artificial light-harvesting molecular architectures
entails building systems that absorb strongly in the visible and near-IR
region of the electromagnetic spectrum and also funnel excited state
energy to a single site. The ability to model nonadiabatic processes,
such as excited-state energy transfer (EET), that occur on a picosecond
time scale can aid in the development of novel artificial light-harvesting
arrays. A combination of density functional theory (DFT), time-dependent
DFT, tight-binding molecular dynamics, and quantum dynamics is employed
here to simulate EET in the ZnFbΦ dyad, a model artificial light-harvesting
array that undergoes EET with an experimentally measured rate constant
of (3.5 ps)−1 upon excitation at 550 nm in toluene
[Yang et al. J. Phys. Chem. B 1998, 102, 9426−9436]. We find that to successfully simulate the
EET process, it is important to (1) include coupling between nuclear
and electronic degrees of freedom in the QD simulation, (2) account
for Coulomb coupling between the electron and hole wavepackets, and
(3) parametrize the extended Hückel model Hamiltonian employed
in the QD simulations with respect to the DFT.