Oriented Triplet Excitons as Long-Lived Electron Spin Qutrits in a Molecular Donor-Acceptor Single Cocrystal.

The photogeneration of multiple unpaired electron spins within molecules is a promising route to applications in quantum information science because they can be initialized into well-defined, multilevel quantum states (S > 1/2) and reproducibly fabricated by chemical synthesis. However, coherent manipulation of these spin states is difficult to realize in typical molecular systems due to the lack of selective addressability and short coherence times of the spin transitions. Here, these challenges are addressed by using donor-acceptor single cocrystals composed of pyrene and naphthalene dianhydride to host spatially oriented triplet excitons, which exhibit promising photogenerated qutrit properties. Time-resolved electron paramagnetic resonance (TREPR) spectroscopy demonstrates that spatially orienting triplet excitons in a single crystal platform imparts narrow, well-resolved, tunable resonances in the triplet EPR spectrum, allowing selective addressability of the spin sublevel transitions. Pulse-EPR spectroscopy reveals that at temperatures above 30 K, spin decoherence of these triplet excitons is driven by exciton diffusion. However, coherence is limited by electronic spin dipolar coupling below 30 K, where T2 varies nonlinearly with the optical excitation density due to exciton annihilation. Overall, an optimized coherence time of T2 = 7.1 µs at 20 K is achieved. These results provide important insights into designing solid-state molecular excitonic materials with improved spin qutrit properties.

Enhancing Coherence Times of Chromophore-Radical Molecular Qubits and Qudits by Rational Design.

An important criterion for quantum operations is long qubit coherence times. To elucidate the influence of molecular structure on the coherence times of molecular spin qubits and qudits, a series of molecules featuring perylenediimide (PDI) chromophores covalently linked to stable nitroxide radicals were synthesized and investigated by pulse electron paramagnetic resonance spectroscopy. Photoexcitation of PDI in these systems creates an excited quartet state (Q) followed by a spin-polarized doublet ground state (D0), which hold promise as spin qudits and qubits, respectively. By tailoring the molecular structure of these spin qudit/qubit candidates by selective deuteration and eliminating intramolecular motion, coherence times of Tm = 9.1 ± 0.3 and 4.2 ± 0.3 µs at 85 K for D0 and Q, respectively, are achieved. These coherence times represent a nearly 3-fold enhancement compared to those of the initial molecular design. This approach offers a rational structural design protocol for effectively extending coherence times in molecular spin qudits/qubits.

Quantum Gate Operations on a Spectrally Addressable Photogenerated Molecular Electron Spin-Qubit Pair.

Sub-nanosecond photodriven electron transfer from a molecular donor to an acceptor can be used to generate a radical pair (RP) having two entangled electron spins in a well-defined pure initial singlet quantum state to serve as a spin-qubit pair (SQP). Achieving good spin-qubit addressability is challenging because many organic radical ions have large hyperfine couplings (HFCs) in addition to significant g-anisotropy, which results in significant spectral overlap. Moreover, using radicals with g-factors that deviate significantly from that of the free electron results in difficulty generating microwave pulses with sufficiently large bandwidths to manipulate the two spins either simultaneously or selectively as is necessary to implement the controlled-NOT (CNOT) quantum gate essential for quantum algorithms. Here, we address these issues by using a covalently linked donor-acceptor(1)-acceptor(2) (D-A1-A2) molecule with significantly reduced HFCs that uses fully deuterated peri-xanthenoxanthene (PXX) as D, naphthalenemonoimide (NMI) as A1, and a C60 derivative as A2. Selective photoexcitation of PXX within PXX-d9-NMI-C60 results in sub-nanosecond, two-step electron transfer to generate the long-lived PXX•+-d9-NMI-C60•- SQP. Alignment of PXX•+-d9-NMI-C60•- in the nematic liquid crystal 4-cyano-4'-(n-pentyl)biphenyl (5CB) at cryogenic temperatures results in well-resolved, narrow resonances for each electron spin. We demonstrate both single-qubit gate and two-qubit CNOT gate operations using both selective and nonselective Gaussian-shaped microwave pulses and broadband spectral detection of the spin states following the gate operations.

Spin-Frustrated Trisradical Trication of PrismCage.

Organic trisradicals featuring threefold symmetry have attracted significant interest because of their unique magnetic properties associated with spin frustration. Herein, we describe the synthesis and characterization of a triangular prism-shaped organic cage for which we have coined the name PrismCage6+ and its trisradical trication─TR3(•+). PrismCage6+ is composed of three 4,4'-bipyridinium dications and two 1,3,5-phenylene units bridged by six methylene groups. In the solid state, PrismCage6+ adopts a highly twisted conformation with close to C3 symmetry as a result of encapsulating one PF6- anion as a guest. PrismCage6+ undergoes stepwise reduction to its mono-, di-, and trisradical cations in MeCN on account of strong electronic communication between its 4,4'-bipyridinium units. TR3(•+), which is obtained by the reduction of PrismCage6+ employing CoCp2, adopts a triangular prism-shaped conformation with close to C2v symmetry in the solid state. Temperature-dependent continuous-wave and nutation-frequency-selective electron paramagnetic resonance spectra of TR3(•+) in frozen N,N-dimethylformamide indicate its doublet ground state. The doublet-quartet energy gap of TR3(•+) is estimated to be -0.08 kcal mol-1, and the critical temperature of spin-state conversion is found to be ca. 50 K, suggesting that it displays pronounced spin frustration at the molecular level. To the best of our knowledge, this example is the first organic radical cage to exhibit spin frustration. The trisradical trication of PrismCage6+ opens up new possibilities for fundamental investigations and potential applications in the fields of both organic cages and spin chemistry.

Pulse sequences for manipulating the spin states of molecular radical-pair-based electron spin qubit systems for quantum information applications.

Molecular qubits are an emerging platform in quantum information science due to the unmatched structural control that chemical design and synthesis provide compared to other leading qubit technologies. This theoretical study investigates pulse sequence protocols for spin-correlated radical pairs, which are important molecular spin qubit pair (SQP) candidates. Here, we introduce improved microwave pulse protocols for enhancing the execution times of quantum logic gates based on SQPs. Significantly, this study demonstrates that the proposed pulse sequences effectively remove certain contributions from nuclear spin effects on spin dynamics, which are a common source of decoherence. Additionally, we have analyzed the factors that control the fidelity of the SQP spin state, following the application of the controlled-NOT gate. It was found that higher magnetic fields introduce a high frequency oscillation in the fidelity. Thereupon, it is suggested that further research should be geared toward executing quantum gates at lower magnetic field values. In addition, an absolute bound of the fidelity outcome due to decoherence is determined, which clearly identifies the important factors that control gate execution. Finally, examples of the application of these pulse sequences to SQPs are described.

Optical Spin Polarization of a Narrow-Linewidth Electron-Spin Qubit in a Chromophore/Stable-Radical System.

Photoexcited organic chromophores appended to stable radicals can serve as qubit and/or qudit candidates for quantum information applications. 1,6,7,12-Tetra-(4-tert-butylphenoxy)-perylene-3,4 : 9,10-bis(dicarboximide) (tpPDI) linked to a partially deuterated α,γ-bisdiphenylene-ß-phenylallyl radical (BDPA-d16 ) was synthesized and characterized by time-resolved optical and electron paramagnetic resonance (EPR) spectroscopies. Photoexcitation of tpPDI-BDPA-d16 results in ultrafast radical-enhanced intersystem crossing to produce a quartet state (Q) followed by formation of a spin-polarized doublet ground state (D0 ). Pulse-EPR experiments confirmed the spin multiplicity of Q and yielded coherence times of Tm =2.1±0.1 µs and 2.8±0.2 µs for Q and D0 , respectively. BDPA-d16 eliminates the dominant 1 H hyperfine couplings, resulting in a single narrow line for both the Q and D0 states, which enhances the spectral resolution needed for good qubit addressability.

Evidence of a Uranium-Paddlewheel Node in a Catecholate-Based Metal-Organic Framework.

The interactions between uranium and non-innocent organic species are an essential component of fundamental uranium redox chemistry. However, they have seldom been explored in the context of multidimensional, porous materials. Uranium-based metal-organic frameworks (MOFs) offer a new angle to study these interactions, as these self-assembled species stabilize uranium species through immobilization by organic linkers within a crystalline framework, while potentially providing a method for adjusting metal oxidation state through coordination of non-innocent linkers. We report the synthesis of the MOF NU-1700, assembled from U4+ -paddlewheel nodes and catecholate-based linkers. We propose this highly unusual structure, which contains two U4+ ions in a paddlewheel built from four linkers-a first among uranium materials-as a result of extensive characterization via powder X-ray diffraction (PXRD), sorption, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA), in addition to density functional theory (DFT) calculations.

Using Molecular Design to Enhance the Coherence Time of Quintet Multiexcitons Generated by Singlet Fission in Single Crystals.

Multiexciton quintet states, 5(TT), photogenerated in organic semiconductors using singlet fission (SF), consist of four quantum entangled spins, promising to enable new applications in quantum information science. However, the factors that determine the spin coherence of these states remain underexplored. Here, we engineer the packing of tetracene molecules within single crystals of 5,12-bis(tricyclohexylsilylethynyl)tetracene (TCHS-tetracene) to demonstrate a 5(TT) state that exhibits promising spin qubit properties, including a coherence time, T2, = 3 µs at 10 K, a population lifetime, Tpop, = 130 µs at 5 K, and stability even at room temperature. The single-crystal platform also enables global alignment of the spins and, consequently, individual addressability of the spin-sublevel transitions. Decoherence mechanisms, including exciton diffusion, electronic dipolar coupling, and nuclear hyperfine interactions, are elucidated, providing design principles for increasing T2 and the operational temperature of 5(TT). By dynamically decoupling 5(TT) from the surrounding spin bath, T2 = 10 µs is achieved. These results demonstrate the viability of harnessing singlet fission to initiate multiple electron spins in a well-defined quantum state for next-generation molecular-based quantum technologies.

Mechanistic Investigation of Enhanced Catalytic Selectivity toward Alcohol Oxidation with Ce Oxysulfate Clusters.

Ceria-based materials have been highly desired in photocatalytic reactions due to their redox properties and strong oxygen storage and transfer ability. Herein, we report the structures of one CeCe70 oxysulfate cluster and four MCe70 clusters (M = Cu, Ni, Co, and Fe) with the same Ce70 core. As noted, single-crystal X-ray diffraction confirmed the structures of CeCe70 and the MCe70 series, while Raman spectroscopy indicated an increase in oxygen defects upon the introduction of Cu and Fe ions. The clusters catalyzed the oxidation of 4-methoxybenzyl alcohol under ultraviolet light. CuCe70 and FeCe70 exhibited enhanced reactivity compared to CeCe70 and improved aldehyde selectivity compared to control experiments. In comparison with their homogeneous congeners, the CeCe70/MCe70 clusters altered the location of radical generation from the bulk solution to the clusters' surfaces. Mechanistic studies highlight the role of oxygen defects and specific transition metal introduction for efficient photocatalysis. The mechanistic pathway in this study provides insight into how to select or design a highly selective catalyst for photocatalysis.

Quintet-triplet mixing determines the fate of the multiexciton state produced by singlet fission in a terrylenediimide dimer at room temperature.

Singlet fission (SF) is a photophysical process in which one of two adjacent organic molecules absorbs a single photon, resulting in rapid formation of a correlated triplet pair (T1T1) state whose spin dynamics influence the successful generation of uncorrelated triplets (T1). Femtosecond transient visible and near-infrared absorption spectroscopy of a linear terrylene-3,4:11,12-bis(dicarboximide) dimer (TDI2), in which the two TDI molecules are directly linked at one of their imide positions, reveals ultrafast formation of the (T1T1) state. The spin dynamics of the (T1T1) state and the processes leading to uncoupled triplets (T1) were studied at room temperature for TDI2 aligned in 4-cyano-4'-pentylbiphenyl (5CB), a nematic liquid crystal. Time-resolved electron paramagnetic resonance spectroscopy shows that the (T1T1) state has mixed 5(T1T1) and 3(T1T1) character at room temperature. This mixing is magnetic field dependent, resulting in a maximum triplet yield at ∼200 mT. The accessibility of the 3(T1T1) state opens a pathway for triplet-triplet annihilation that produces a single uncorrelated T1 state. The presence of the 5(T1T1) state at room temperature and its relationship with the 1(T1T1) and 3(T1T1) states emphasize that understanding the relationship among different (T1T1) spin states is critical for ensuring high-yield T1 formation from singlet fission.

Spectral Addressability in a Modular Two Qubit System.

The combination of structural precision and reproducibility of synthetic chemistry is perfectly suited for the creation of chemical qubits, the core units of a quantum information science (QIS) system. By exploiting the atomistic control inherent to synthetic chemistry, we address a fundamental question of how the spin-spin distance between two qubits impacts electronic spin coherence. To achieve this goal, we designed a series of molecules featuring two spectrally distinct qubits, an early transition metal, Ti3+, and a late transition metal, Cu2+ with increasing separation between the two metals. Crucially, we also synthesized the monometallic congeners to serve as controls. The spectral separation between the two metals enables us to probe each metal individually in the bimetallic species and compare it with the monometallic control samples. Across a range of 1.2-2.5 nm, we find that electron spins have a negligible effect on coherence times, a finding we attribute to the distinct resonance frequencies. Coherence times are governed, instead, by the distance to nuclear spins on the other qubit's ligand framework. This finding offers guidance for the design of spectrally addressable molecular qubits.

Interaction of Photogenerated Spin Qubit Pairs with a Third Electron Spin in DNA Hairpins.

The designing of tunable molecular systems that can host spin qubits is a promising strategy for advancing the development of quantum information science (QIS) applications. Photogenerated radical pairs are good spin qubit pair (SQP) candidates because they can be initialized in a pure quantum state that exhibits relatively long coherence times. DNA is a well-studied molecular system that allows for control of energetics and spatial specificity through careful design and thus serves as a tunable scaffold on which to control multispin interactions. Here, we examine a series of DNA hairpins that use naphthalenediimide (NDI) as the hairpin linker. Photoexcitation of the NDI leads to subnanosecond oxidation of guanine (G) within the duplex or a stilbenediether (Sd) end-cap to give NDI•--G•+ or NDI•--Sd•+ SQPs, respectively. A 2,2,6,6-tetramethylpiperdinyl-1-oxyl (TEMPO) stable radical is covalently attached to the hairpin at varying distances from the SQP spins. While TEMPO has a minimal effect on the SQP formation and decay dynamics, EPR spectroscopy indicates that there are significant spin-spin dipolar interactions between the SQP and TEMPO. We also demonstrate the ability to implement more complex spin manipulations of the NDI•--Sd•+-TEMPO system using pulse-EPR techniques, which is important for developing DNA hairpins for QIS applications.

Discrete Open-Shell Tris(bipyridinium radical cationic) Inclusion Complexes in the Solid State.

The solid-state properties of organic radicals depend on radical-radical interactions that are influenced by the superstructure of the crystalline phase. Here, we report the synthesis and characterization of a substituted tetracationic cyclophane, cyclobis(paraquat-p-1,4-dimethoxyphenylene), which associates in its bisradical dicationic redox state with the methyl viologen radical cation (MV•+) to give a 1:1 inclusion complex. The (super)structures of the reduced cyclophane and this 1:1 complex in the solid state deviate from the analogous (super)structures observed for the reduced state of cyclobis(paraquat-p-phenylene) and that of its trisradical tricationic complex. Titration experiments reveal that the methoxy substituents on the p-phenylene linkers do not influence binding of the cyclophane toward small neutral guests-such as dimethoxybenzene and tetrathiafulvalene-whereas binding of larger radical cationic guests such as MV•+ by the reduced cyclophane decreases 10-fold. X-ray diffraction analysis reveals that the solid-state superstructure of the 1:1 complex constitutes a discrete entity with weak intermolecular orbital overlap between neighboring complexes. Transient nutation EPR experiments and DFT calculations confirm that the complex has a doublet spin configuration in the ground state as a result of the strong orbital overlap, while the quartet-state spin configuration is higher in energy and inaccessible at ambient temperature. Superconducting quantum interference device (SQUID) measurements reveal that the trisradical tricationic complexes interact antiferromagnetically and form a one-dimensional Heisenberg antiferromagnetic chain along the a-axis of the crystal. These results offer insights into the design and synthesis of organic magnetic materials based on host-guest complexes.

Charge Transfer and Spin Dynamics in a Zinc Porphyrin Donor Covalently Linked to One or Two Naphthalenediimide Acceptors.

Quantum coherence effects on charge transfer and spin dynamics in a system having two degenerate electron acceptors are studied using a zinc 5,10,15-tri(n-pentyl)-20-phenylporphyrin (ZnP) electron donor covalently linked to either one or two naphthalene-1,8:4,5-bis(dicarboximide) (NDI) electron acceptors using an anthracene (An) spacer, ZnP-An-NDI (1) and ZnP-An-NDI2 (2), respectively. Following photoexcitation of 1 and 2 in toluene at 295 K, femtosecond transient absorption spectroscopy shows that the electron transfer (ET) rate constant for 2 is about three times larger than that of 1, which can be accounted for by the statistical nature of incoherent ET as well as the electron couplings for the charge separation reactions. In contrast, the rate constant for charge recombination (CR) of 1 is about 25% faster than that of 2. Using femtosecond transient infrared spectroscopy and theoretical analysis, we find that the electron on NDI2•- in 2 localizes onto one of the two NDIs prior to CR, thus precluding electronically coherent CR from NDI2•-. Conversely, CR in both 1 and 2 is spin coherent as indicated by the observation of a resonance in the 3*ZnP yield following CR as a function of applied magnetic field, giving spin-spin exchange interaction energies of 2J = 210 and 236 mT, respectively, where the line width of the resonance for 2 is greater than 1. These data show that while CR is a spin-coherent process, incoherent hopping of the electron between the two NDIs in 2, consistent with the lack of delocalization noted above, results in greater spin decoherence in 2 relative to 1.

Selectively Addressable Photogenerated Spin Qubit Pairs in DNA Hairpins.

Photoinduced electron transfer can produce radical pairs having two quantum entangled electron spins that can act as spin qubits in quantum information applications. Manipulation of these spin qubits requires selective addressing of each spin using microwave pulses. In this work, photogenerated spin qubit pairs are prepared within chromophore-modified DNA hairpins with varying spin qubit distances, and are probed using transient EPR spectroscopy. By performing pulse-EPR measurements on the shortest hairpin, selective addressing of each spin qubit comprising the pair is demonstrated. Furthermore, these spin qubit pairs have coherence times of more than 4 µs, which provides a comfortable time window for performing complex spin manipulations for quantum information applications. The applicability of these DNA-based photogenerated two-qubit systems is discussed in the context of quantum gate operations, specifically the controlled-NOT gate.

Using Photoexcited Core/Shell Quantum Dots To Spin Polarize Appended Radical Qubits.

The synthetic tunability, flexibility, and rich spin physics of semiconductor quantum dots (QDs) make them promising candidates for quantum information science applications. However, the rapid spin relaxation observed in colloidal quantum dots limits their functionality. In the current work, we demonstrate a method to harness photoexcited spin states in QDs to produce long-lived spin polarization on an appended organic ligand molecule. We present a system composed of CdSe/CdS core/shell QDs, covalently linked to naphthalenediimide (NDI) electron-accepting molecules. The electron transfer dynamics from photoexcited QDs to the appended NDI ligands is explored as a function of both shell thickness and number of NDIs per QD. Transient EPR spectroscopy shows that the photoexcited QDs strongly spin polarize the NDI radical anion, which is interpreted in the context of both the radical pair and the triplet mechanisms of spin polarization. This work serves as an initial step toward using photoexcited QDs to strongly spin polarize organic radicals having long spin relaxation times to serve as spin qubits in quantum information science applications.

Insights into the Enhanced Catalytic Activity of Cytochrome c When Encapsulated in a Metal-Organic Framework.

The encapsulation of enzymes within porous materials has shown great promise, not only in protecting the enzymes from denaturation under nonbiological environments, but also, in some cases, in facilitating their enzymatic reaction rates at favorable reaction conditions. While a number of hypotheses have been developed to explain this phenomenon, the detailed structural changes of the enzymes upon encapsulation within the porous material, which are closely related to their activity, remain largely elusive. Herein, the structural change of cytochrome c (Cyt c) upon encapsulation within a hierarchical metal-organic framework, NU-1000, is investigated through a combination of experimental and computational methods, such as electron paramagnetic resonance, solid-state ultraviolet-visible spectroscopy, and all-atom explicit solvent molecular dynamics simulations. The enhanced catalytic performance of Cyt c after being encapsulated within NU-1000 is supported by the physical and in silico observations of a change around the heme ferric active center.

Metalated Porphyrin Stable Free Radicals: Exploration of Electron Spin Communication and Dynamics.

Switchable coupling between two qubits is important for quantum information science (QIS). As a proof of concept, a series of mesosubstituted porphyrins have been synthesized with a (2,2,6,6-tetramethylpiperidin-1-yl)oxyl stable free radical (SFR) appended and metalated with Cu(II), Ni(II), and Zn(II) in order to explore the interaction between the SFR doublet state and metalloporphyrin. The spin state of the porphyrin varies upon metal insertion, where Zn(II) is a diamagnetic metal, Cu(II) is paramagnetic, and Ni(II) can be switched from a diamagnetic square-planar structure to a paramagnetic octahedral state by complexation with a solvent (i.e., pyridine or tetrahydrofuran). Time-resolved electron paramagnetic resonance (EPR) measurements reveal that upon photoexcitation, the Zn(II) and free-base porphyrin species demonstrate different magnetic exchange regimes between the porphyrin triplet excited states and the SFR doublet state, with the Zn derivative populating a quartet state (i.e., moderate magnetic exchange), whereas the free-base derivative remains a triplet (i.e., weak magnetic exchange). Transient absorption measurements corroborate the TREPR results, demonstrating a 66% increase in the singlet excited-state decay rate due to enhanced intersystem crossing for the Zn(II) derivative in comparison to a modest 14% enhancement for the free-base porphyrin. These results enable the realization of a switchable qubit coupler, depending upon Zn metal insertion to the free-base porphyrin, which has potential QIS applications.

CNOT gate operation on a photogenerated molecular electron spin-qubit pair.

Implementation of the two-qubit controlled-NOT (CNOT) gate is necessary to develop a complete set of universal gates for quantum computing. Here, we demonstrate that a photogenerated radical (spin qubit) pair within a covalent donor-chromophore-acceptor molecule can be used to successfully execute a CNOT gate with high fidelity. The donor is tetrathiafulvalene (TTF), the chromophore is 8-aminonaphthalene-1,8-dicarboximide (ANI), and the acceptor is pyromellitimide (PI). Selective photoexcitation of ANI with a 416 nm laser pulse results in subnanosecond formation of the TTF•+-ANI-PI•- radical (spin qubit) pair at 85 K having a 1.8 µs phase memory time. This is sufficiently long to execute a CNOT gate using a sequence of five microwave pulses followed by a sequence of two pulses that read out all the elements of the density matrix. Comparing these data to a simulation of the data that assumes ideal conditions results in a fidelity of 0.97 for the execution of the CNOT gate. These results show that photogenerated molecular spin qubit pairs can be used to execute this essential quantum gate at modest temperatures, which affords the possibility that chemical synthesis can be used to develop structures to execute more complex quantum logic operations using electron spins.

Photogenerated Spin-Entangled Qubit (Radical) Pairs in DNA Hairpins: Observation of Spin Delocalization and Coherence.

The ability to prepare physical qubits in specific initial quantum states is a critical requirement for their use in quantum information science (QIS). Subnanosecond photoinduced electron transfer in a structurally well-defined donor-acceptor system can be used to produce an entangled spin qubit (radical) pair in a pure initial singlet state fulfilling this criterion. Synthetic DNA is a promising platform on which to build spin qubit arrays with fixed spatial relationships; therefore, we have prepared a series of DNA hairpins in which naphthalenediimide (NDI) is the chromophore/acceptor hairpin linker, variable-length diblock A- and G-tracts are intermediate donors, and a stilbenediether (Sd) is the terminal donor. Photoexcitation of NDI in these DNA hairpins generates high-yield, long-lived, entangled spin qubit pairs at 85 K, and time-resolved and pulse electron paramagnetic resonance (EPR) spectroscopies are used to probe their spin dynamics. Specifically, measurements of the distance-dependent dipolar coupling between the two spins are used to obtain the average spin qubit pair distance in the absence of the terminal Sd donor and reveal that one of the spins is fully delocalized across up to five adjacent guanines in a G-tract on the EPR time scale. We have recently shown that extensive spin hopping between degenerate sites accessible to one spin of the pair may result in spin decoherence. However, we observe a strong out-of-phase electron spin echo envelope modulation (OOP-ESEEM) signal from the NDI•--Sd•+ spin qubit pair in DNA hairpins showing that spin coherence is maintained across a 2 adenine A-tract followed by a 2-4 guanine G-tract as a result of rapid spin transport to Sd. These results demonstrate that pulse-EPR can manipulate coherent spin states in DNA hairpins, which is essential for quantum gate operations relevant to QIS applications.