Molecules provide a modular and chemically tunable platform for quantum information science. In recent years, significant advances have been made in enabling optical spin initialization, coherent control, and both optical and electrical readout of molecular qubits. Yet, a central challenge remains: realizing scalable architectures through the controlled and ultrafast activation of interqubit interactions. Here, we present a molecular system composed of two vanadyl porphyrin qubits bridged by a free-base porphyrin chromophore, where the qubits are magnetically independent in the ground state but become coupled upon photoexcitation. Femtosecond transient absorption and time-resolved electron paramagnetic resonance experiments, supported by DFT calculations and spectral simulations, reveal that photoexcitation induces the formation of a spin-quintet state within subpicosecond time scales. Notably, long-lived spin polarization persists up to room temperature. Theoretical modeling offers design principles for harnessing this mechanism in future applications. These results provide a proof of concept for optically controlled spin interactions in molecules, paving the way for light-activated molecular quantum gates.

Spin-selective charge-transfer pathways in helicene-based dyads are relevant to applications ranging from energy conversion to quantum information science. Here, we report a series of molecular systems comprising a thiahelicene donor and a perylenediimide (PDI) acceptor connected by oligophenyl bridges of varying length. The influence of donor-acceptor distance and relative orientation on the photophysical and spin-selective properties is investigated using a combined approach based on DFT calculations, transient absorption, and time-resolved electron paramagnetic resonance spectroscopies. Particular attention is given to the role of the bridge in tuning the magnetic exchange coupling within charge-transfer states and its impact on spin-selective recombination pathways to the PDI triplet state. Efficient formation of long-lived PDI triplets is observed and shown to sensitize singlet oxygen generation with high efficiencies. These results establish structure-property relationships governing spin-selective processes in helicene-based dyads.

Chirality-induced spin selectivity (CISS) revealed a close connection between molecular chirality and electron spin. Because CISS is observed even at room temperature, it offers a promising route toward spin-based technologies operable under ambient conditions. However, its microscopic origin remains the subject of debate. In recent theories, the parameters governing the electron motion through the chiral bridge play a key role in CISS efficiency. To disentangle this specific contribution from that arising from the overall intrinsic chirality of the molecule, we synthesized a new chiral donor-acceptor dyad (Dχ-B-A) incorporating a thia-bridged[4]helicene donor, known to have high CISS efficiency in transport experiments, and a perylene diimide (PDI) acceptor connected by a three-ethynylbenzene bridge. Transient absorption measurements at 85 K show that photoexcitation of PDI generates a long-lived radical pair (Dχ·+-B-A·-) with a lifetime exceeding 500 ns. The combined analysis of the spin polarization mechanism using time-resolved electron paramagnetic resonance, DFT calculations, and theoretical modeling indicates weak CISS polarization and suggests that CISS efficiency is higher in the presence of a chiral bridge.

Molecular multi-spin systems acting as potential quantum gates require fine-tuning magnetic interactions to achieve single spin addressability and entanglement of the spin qubits. We report here the synthesis of a new singly linked vanadyl-porphyrin dimer that crystallizes in two different pseudo-polymorphs. The single crystal continuous-wave Electron Paramagnetic Resonance investigation evidences a small but crucial isotropic exchange interaction, J, between the two tilted, and thus distinguishable, spin centers of the order of 10^-2 cm-1. The experimental and DFT studies evidence a correlation between J values and porphyrin planes tilting angle and distortion. Pulsed EPR analysis shows that the two vanadyl dimers maintain the coherence time of the monomer. Our results, coupled with the evaporability of porphyrin systems, establish this class of dimers as extremely promising for quantum information processing applications.

Investigating Chirality-Induced Spin Selectivity (CISS) at the molecular level offers a novel perspective, in between Chemistry and Physics, on this still not fully understood phenomenon. Indeed, the molecular approach offers an advantage point for understanding CISS by disentangling the role of chiral molecules from that of the surfaces. Here, we present an overview of experimental observations of CISS in electron transfer on isolated molecules in solution and the current status of theory to model the phenomenon. We discuss what is accomplished and which are the most important questions, and we propose experiments based on electron and nuclear magnetic resonance both to unravel open issues on the CISS effect in electron transfer and to apply it to quantum technologies.

The intrinsic quantum nature of molecules opens exciting opportunities for developing the field of quantum information science. In this context, porphyrins stand out as ideal building blocks for quantum technologies thanks to their unique optical and electrical properties as well as their capacity to accommodate metal atoms and ions. This review bridges the chemistry and physics of porphyrins, providing an overview of recent advances in porphyrin-based molecular qubits. Starting from qubits, the review explores the potential of porphyrin units to combine, leading to the formation of quantum logic gates and hierarchical higher-dimensional structures. Next, the exploitation of porphyrins' unique photophysical properties for realizing long-lived high spin states is examined. These states are promising for the photogeneration of multi-level systems and the optical initialization and control of molecular qubits. With a critical eye on the current state-of-the-art, the review elucidates the future perspectives of porphyrins for advancing quantum technologies. Porphyrins represent ideal building blocks for quantum information science. Their ability to accommodate metal ions makes them an excellent platform for quantum bits. Their distinctive molecular structure enables the formation of quantum logic gates and higher-dimensional systems. Their molecular stability makes them highly suitable for surface processing. Lastly, their unique optical properties hold promise for photoinduced applications. image

Photoexcited organic chromophores appended to molecular qubits can serve as a source of spin initialization or multilevel qudit generation for quantum information applications. So far, this approach has been primarily investigated in chromophore-stable radical systems. Here, we extend this concept to a meso-meso linked oxovanadium(IV) porphyrin-free-base porphyrin dimer. Femtosecond transient absorption experiments reveal that photoexcitation of the free-base porphyrin leads to picosecond triplet state formation via enhanced intersystem crossing. Time-resolved electron paramagnetic resonance (TREPR) experiments carried out at both 85 K and room temperature reveal the formation of a long-lived spin-polarized quartet state through triplet-doublet spin mixing. Notably, a distinct hyperfine structure arising from the interaction between the electron spin quartet state and the vanadyl nucleus (51V, I = 7/2) is evident, with the quartet state showing long-lived spin polarization even at room temperature. Theoretical simulations of the TREPR spectra confirm the photogenerated quartet state and provide insights into the non-Boltzmann spin populations. Exploiting this phenomenon affords the possibility of using photoinduced triplet states in porphyrins for quantum information as a resource to polarize and magnetically couple molecular electronic or nuclear spin qubits and qudits.

Free charge generation after photoexcitation of donor or acceptor molecules in organic solar cells generally proceeds via (1) formation of charge transfer states and (2) their dissociation into charge separated states. Research often either focuses on the first component or the combined effect of both processes. Here, we provide evidence that charge transfer state dissociation rather than formation presents a major bottleneck for free charge generation in fullerene-based blends with low energetic offsets between singlet and charge transfer states. We investigate devices based on dilute donor content blends of (fluorinated) ZnPc:C60 and perform density functional theory calculations, device characterization, transient absorption spectroscopy and time-resolved electron paramagnetic resonance measurements. We draw a comprehensive picture of how energies and transitions between singlet, charge transfer, and charge separated states change upon ZnPc fluorination. We find that a significant reduction in photocurrent can be attributed to increasingly inefficient charge transfer state dissociation. With this, our work highlights potential reasons why low offset fullerene systems do not show the high performance of non-fullerene acceptors. Fullerene acceptors are relevant for upscaling industrial production of organic solar cells. Here, authors reveal that for donor-acceptor blends with low energetic offset, charge transfer state dissociation rather than charge transfer state formation presents a bottleneck for free charge generation.

Organic luminescent materials that exhibit thermally activated delayed fluorescence (TADF) can convert non-emissive triplet excitons into emissive singlet states through a reverse intersystem crossing (RISC) process. Therefore, they have tremendous potential for applications in organic light-emitting diodes (OLEDs). However, with the development of ultra-high definition 4K/8K display technologies, designing efficient deep-blue TADF materials to achieve the Commission Internationale de l'Éclairage (CIE) coordinates fulfilling BT.2020 remains a significant challenge. Here, an effective approach is proposed to design deep-blue TADF molecules based on hybrid long- and short-range charge-transfer by incorporation of multiple donor moieties into organoboron multiple resonance acceptors. The resulting TADF molecule exhibits deep-blue emission at 414 nm with a full width at half maximum (FWHM) of 29 nm, together with a thousand-fold increase in RISC rate. OLEDs based on the champion material achieve a record maximum external quantum efficiency (EQE) of 22.8% with CIE coordinates of (0.163, 0.046), approaching the coordinates of the BT.2020 blue standard. Moreover, TADF-assisted fluorescence devices employing the designed material as a sensitizer exhibit an exceptional EQE of 33.1%. This work thus provides a blueprint for future development of efficient deep-blue TADF emitters, representing an important milestone towards meeting the blue color gamut standard of BT.2020.

Copper-poor Cu2ZnSnS4 (copper zinc tin sulfide, CZTS) inorganic semiconducting nanoparticles were synthesized by an environmentally friendly low-temperature (100 degrees C) synthetic path, which allows precise control of the Sn content without any relevant presence of Zn- and Sn-related secondary phases. The resulting nanoparticles are polycrystalline and quasi-spherical, with an average diameter of 10 nm. The shape and composition were assessed using a multitechnique approach based on X-ray photoelectron spectroscopy (XPS), energy-dispersive fluorescence X-ray spectroscopy (EDXRF), inductively coupled plasma atomic emission spectrometry (ICP-AES), and high-resolution transmission electron microscopy (HR-TEM). The presence of paramagnetic species associated with Cu2+ cations was highlighted by electron paramagnetic resonance (EPR) spectroscopy, pinpointing the presence of significant exchange interactions between Cu2+ ions. The mixed oxidation state of Cu induces the generation of free holes, which are confined in the nanoparticles, giving rise to a plasmonic resonance. The plasmonic properties were investigated as a function of Sn doping through vis-NIR absorption spectroscopy combined with magnetic circular dichroism (MCD). This approach enabled the extraction of charge carriers' density and mass, a key step for further optimization of CZTS-based photovoltaic devices.

In the development of two-qubit quantum gates, precise control over the intramolecular spin-spin interaction between molecular spin units plays a pivotal role. A weak but measurable exchange coupling is especially important for achieving selective spin addressability that allows controlled manipulation of the computational basis states |00⟩ |01⟩ |10⟩ |11⟩ by microwave pulses. Here, we report the synthesis and Electron Paramagnetic Resonance (EPR) study of a heterometallic meso-meso (m-m) singly-linked V IV O−Cu II porphyrin dimer. X-band continuous wave EPR measurements in frozen solutions suggest a ferromagnetic exchange coupling of ca. 8 ⋅ 10 −3  cm −1 . This estimation is supported by Density Functional Theory calculations, which also allow disentangling the ferro- and antiferromagnetic contributions to the exchange. Pulsed EPR experiments show that the dimer maintains relaxation times similar to the monometallic Cu II porphyrins. The addressability of the two individual spins is made possible by the different g -tensors of V IV and Cu II -ions, in contrast to homometallic dimers where tilting of the porphyrin planes plays a key role. Therefore, single-spin addressability in the heterometallic dimer can be maintained even with small tilting angles, as expected when deposited on surface, unlocking the full potential of molecular quantum gates for practical applications.

Data supporting the original figures 2, 3, 4. and 5 of the related publication.

Molecular spins are promising building blocks of future quantum technologies thanks to the unparalleled flexibility provided by chemistry, which allows the design of complex structures targeted for specific applications. However, their weak interaction with external stimuli makes it difficult to access their state at the single-molecule level, a fundamental tool for their use, for example, in quantum computing and sensing. Here, an innovative solution exploiting the interplay between chirality and magnetism using the chirality-induced spin selectivity effect on electron transfer processes is foreseen. It is envisioned to use a spin-to-charge conversion mechanism that can be realized by connecting a molecular spin qubit to a dyad where an electron donor and an electron acceptor are linked by a chiral bridge. By numerical simulations based on realistic parameters, it is shown that the chirality-induced spin selectivity effect could enable initialization, manipulation, and single-spin readout of molecular qubits and qudits even at relatively high temperatures.

The poor operational stability of non-fullerene electron acceptor (NFA) organic solar cells (OSCs) currently limits their commercial application. While previous studies have primarily focused on the degradation of the NFA component, we also consider here the electron donor material. We examine the stability of three representative donor polymers, PM6, D18, and PTQ10, paired with the benchmark NFA, Y6. After light soaking PM6 and D18 in air, we find an enhanced conversion of singlet excitons into trapped interchain polaron pairs on sub-100 femtosecond timescales. This process outcompetes electron transfer to Y6, significantly reducing the charge generation yield. However, this pathway is absent in PTQ10. We identify twisting in the benzo[1,2-b:4,5-b′]dithiophene (BDT)-thiophene motif shared by PM6 and D18 as the cause. By contrast, PTQ10 does not contain this structural motif and has improved stability. Thus, we show that the donor polymer can be a weak link for OSC stability, which must be addressed collectively with the NFA.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Over the past two decades, the chirality-induced spin selectivity (CISS) effect was reported in several experiments disclosing a unique connection between chirality and electron spin. Recent theoretical works have highlighted time-resolved Electron Paramagnetic Resonance (trEPR) as a powerful tool to directly detect the spin polarisation resulting from CISS. Because of the absence of interfaces with conducting electrodes, such spectroscopic evidence could provide a clear understanding of how CISS works at the intramolecular level. Experimental results have demonstrated the potential of this approach for detecting a spin-polarised photoinduced electron transfer (ET) in hybrid systems comprising a CdSe quantum dot as an electron donor (D) connected by a chiral linker (χ) to a fullerene derivative as an electron acceptor (A). However, the study of the ET process in fully organic D-χ-A dyads holds tremendous potential for the unambiguous detection of CISS. Here, we report a first attempt performed using novel D-χ-A dyads, comprising pyrene (D) and fullerene (A) connected by chiral saturated peptide bridges (χ) of different length and electric dipole moment. The dyads are investigated by an array of techniques, including cyclic voltammetry, optical spectroscopies, and trEPR. Despite the promising energy alignment of the electronic levels and the evidence of luminescence quenching, trEPR does not detect a significant ET highlighting the challenges of spectroscopic detection of CISS. However, the analysis allows the formulation of guidelines for the design of chiral organic model systems suitable to directly probe CISS-polarised ET.

It is well assessed that the charge transport through a chiral potential barrier can result in spin-polarized charges. The possibility of driving this process through visible photons holds tremendous potential for several aspects of quantum information science, e.g., the optical control and readout of qubits. In this context, the direct observation of this phenomenon via spin-sensitive spectroscopies is of utmost importance to establish future guidelines to control photo-driven spin selectivity in chiral structures. Here, we provide direct proof that time-resolved electron paramagnetic resonance (EPR) can be used to detect long-lived spin polarization generated by photoinduced charge transfer through a chiral bridge. We propose a system comprising CdSe quantum dots (QDs), as a donor, and C60, as an acceptor, covalently linked through a saturated oligopeptide helical bridge (χ) with a rigid structure of ∼10 Å. Time-resolved EPR spectroscopy shows that the charge transfer in our system results in a C60 radical anion, whose spin polarization maximum is observed at longer times with respect to that of the photogenerated C60 triplet state. Notably, the theoretical modelling of the EPR spectra reveals that the observed features may be compatible with chirality-induced spin selectivity, but the electronic features of the QD do not allow the unambiguous identification of the CISS effect. Nevertheless, we identify which parameters need optimization for unambiguous detection and quantification of the phenomenon. This work lays the basis for the optical generation and direct manipulation of spin polarization induced by chirality.

Organic solar cells (OSCs) have recently shown a rapid improvement in their performance, bringing power conversion efficiencies to above 18%. However, the open‐circuit voltage of OSCs remains low relative to their optical gap and this currently limits efficiency. Recombination to spin‐triplet excitons is a key contributing factor, and is widely, but not universally, observed in donor–acceptor blends using both fullerene and nonfullerenes as electron acceptors. Here, an experimental framework that combines time‐resolved optical and magnetic resonance spectroscopies to detect triplet excitons and identify their formation mechanisms, is reported. The methodology is applied to two well‐studied polymer:fullerene systems, PM6:PC60BM and PTB7‐Th:PC60BM. In contrast to the more efficient nonfullerene acceptor systems that show only triplet states formed via nongeminate recombination, the fullerene systems also show significant triplet formation via geminate processes. This requires that geminate electron–hole pairs be trapped long enough to allow intersystem crossing. It is proposed that this is a general feature of fullerene acceptor systems, where isolated fullerenes are known to intercalate within the alkyl sidechains of the donor polymers. Thus, the study demonstrates that engineering good donor and acceptor domain purity is key for suppressing losses via triplet excitons in OSCs.