Characterization of Photogenerated Spin Qubit Pairs in Various Dye Derivative - ZnO QD Conjugates

Previously, we have shown that upon photoexcitation of a dye molecule - quantum dot conjugated system a charge separated state can be induced. This charge separated state possess two formerly spin-paired electrons that reside in spatially separated sites, nominally labeled as spin-correlated radical pairs (SCRPs). SCRPs, also referred to as spin qubit pairs (SQPs), have unique properties which are applicable to quantum information science. These systems can act as quantum bits, qubits, operating at moderate temperatures with well-defined quantum states. In this work, we aim to expand our understanding regarding the effect that distance between dye and quantum dot (QD) has on the presence and lifetime of SQPs. We examine this causal relationship by utilizing various linker lengths, allowing us to examine a range of distances between the QD and the dye. The specific system we have chosen to study involves various carboxylate dye molecules, perylene and BPEA derivatives, and ZnO QDs. We first study their chemical interactions using absorption isotherms and then measure the photophysics of these conjugates using both steady-state and time-resolved photoluminescence spectroscopy. Swift photoinduced electron transfer from the dye derivatives to the ZnO QD is observed, and a long-lived (> 7 ns) charge separated state is generated. This charge separated state is then analyzed using laser induced time-resolved electron paramagnetic resonance spectroscopy to fully characterize the spin dynamics of the photogenerated SQPs.