Two-Photon Absorption in Electron Donor-Acceptor Dyads and Triads Using Classical and Entangled Photons: Potential Systems for Photon-to-Spin Quantum Transduction

Photon-to-spin quantum transduction, i.e., the exchange of coherence between photons and spins, is important for establishing links between localized molecular qubit systems performing logic and/or sensing operations and similar systems at different physical locations. We are developing molecular systems to explore how transduction can be implemented by using entangled photons to produce entangled spin pairs by ultrafast electron transfer leading to spin-correlated radical pairs (SCRPs). We have prepared and systematically evaluated electron transfer dyads and triads based on a 9-(N-piperidinyl)perylene-3,4-dicarboximide (6PMI) donor, a naphthalene-1,8:4,5-bis(dicarboximide) (NDI) acceptor, and a tetrathiofulvalene (TTF) secondary donor, which are prepared with and without a phenyl spacer between the 6PMI and NDI to give 6PMI-NDI, 6PMI-Ph-NDI, TTF-6PMI-NDI, and TTF-6PMI-Ph-NDI. We used transient absorption, fluorescence-detected classical two-photon-absorption, and entangled two-photon-absorption (ETPA) spectroscopies to characterize the optical properties of these systems, while time-resolved EPR spectroscopy was used to characterize their photogenerated SCRPs. The results show that the ETPA cross section depends entirely on the presence of 6PMI and NDI in the 6PMI-NDI and 6PMI-Ph-NDI dyads, but in the triads TTF-6PMI-NDI and TTF-6PMI-Ph-NDI, the presence of the Ph spacer significantly affects the ETPA cross section. These results provide important information for designing molecular systems to implement photon-to-spin quantum transduction using entangled photons.