Quantum coherence controls the charge separation in a prototypical artificial light-harvesting system

Abstract

The efficient conversion of light into electricity or chemical fuels is a fundamental challenge. In artificial photosynthetic and photovoltaic devices, this conversion is generally thought to happen on ultrafast, femto-to-picosecond timescales and to involve an incoherent electron transfer process. In some biological systems, however, there is growing evidence that the coherent motion of electronic wavepackets is an essential primary step, raising questions about the role of quantum coherence in artificial devices. Here we investigate the primary charge-transfer process in a supramolecular triad, a prototypical artificial reaction centre. Combining high time-resolution femtosecond spectroscopy and time-dependent density functional theory, we provide compelling evidence that the driving mechanism of the photoinduced current generation cycle is a correlated wavelike motion of electrons and nuclei on a timescale of few tens of femtoseconds. We highlight the fundamental role of the interface between chromophore and charge acceptor in triggering the coherent wavelike electron-hole splitting.

Charge transfer in time-dependent density-functional theory: Insights from the asymmetric Hubbard dimer

“…If, instead, the charge-transfer occurs from an already-excited state, for example, as modelled by the computation in Ref. [10] where the initial state is the photoexcited carotenoid triad, the situation is quite different, since there is not necessarily the fundamental change in the form of the interacting state described above. For example, in the case of closed-shell fragments, an initial local excitation on one fragment breaks the double occupation of the HOMO on the donor and, if the KS initial state is chosen appropriately, it could more naturally model the transfer of one electron from the donor to the acceptor, reducing the correlation effects.…”

“…Still, a truly time-resolved description must go beyond a calculation of the excitation spectrum: electron transfer between regions of space is clearly nonperturbative. TDDFT certainly applies in the nonlinear regime and has given useful predictions in many cases, including CT dynamics [10]. At the same time, there is a dearth of alternative accurate practical methods to test TDDFT calculations.…”

Tracking the coherent generation of polaron pairs in conjugated polymers

“…Recent theoretical work2324 suggests that strong coherent coupling between electronic and vibrational degrees of freedom, that is, vibronic coupling, may lie at the origin of this efficient polaron pair formation, similar to seminal models for polaron motion in solids25. Such a picture would underpin emerging experimental and theoretical evidence that vibronic couplings are important for photoinduced energy and charge transfer processes in biological and artificial light-harvesting systems2627282930 or organic solar cells at room temperature313233. Yet, at present, it is unclear to what extent vibronic quantum coherence34353637 affects the optical properties of thin polymer films at room temperature.…”

Interlayer‐State‐Coupling Dependent Ultrafast Charge Transfer in MoS2/WS2 Bilayers

“…The interlayer charge transfer in MX 2 heterostructures is of central importance in their photoresponse, which determines both the speed and efficiency of the charge separation 35, 36. Since the charge transfer is mainly through the overlapping between interlayer electronic states, the charge transfer process is believed to be highly dependent on the interlayer stackings (twisting, translation, and spacing) and interactions.…”