Light-driven electron transfer by Quantum vibronic ratcheting

The optical control of coherence to improve and create a new molecular function is a grand challenge in science. In this work, we present a synthetic strategy to build a donor-donor-acceptor (D1D2A) supramolecular construct and tailor vibronic coherence to leverage an efficient long-range electron-transfer by defeating the thermodynamic energy trap imposed by Boltzmann statistics. The relaxed D1* lies 0.35 eV below the D2* state. By a combined transient IR and two-dimensional electronic vibrational spectroscopy study we show that selective excitation of the vibronic bands of lower energy primary donor (D1) leads to substantial rapid (< 200 fs) formation of a charge-transfer state (D1D2+A−), followed by hole transfer leading to (D1+D2A−). This provides direct evidence of electron transfer (secondary donor D2 to A) induced by a vibronic quantum ratcheted ‘uphill’ energy transfer from D1 to D2. Thus, it lays out a rational for improving efficiency of solar energy conversion and expanding the spectral bandwidth in synthetic light harvesting systems.