Pathogenesis of human B cell lymphomas.

The mechanisms that drive normal B cell differentiation and activation are frequently subverted by B cell lymphomas for their unlimited growth and survival. B cells are particularly prone to malignant transformation because the machinery used for antibody diversification can cause chromosomal translocations and oncogenic mutations. The advent of functional and structural genomics has greatly accelerated our understanding of oncogenic mechanisms in lymphomagenesis. The signaling pathways that normal B cells utilize to sense antigens are frequently derailed in B cell malignancies, leading to constitutive activation of prosurvival pathways. These malignancies co-opt transcriptional regulatory systems that characterize their normal B cell counterparts and frequently alter epigenetic regulators of chromatin structure and gene expression. These mechanistic insights are ushering in an era of targeted therapies for these cancers based on the principles of pathogenesis.

Electron-catalysed molecular recognition.

Molecular recognition1-4 and supramolecular assembly5-8 cover a broad spectrum9-11 of non-covalently orchestrated phenomena between molecules. Catalysis12 of such processes, however, unlike that for the formation of covalent bonds, is limited to approaches13-16 that rely on sophisticated catalyst design. Here we establish a simple and versatile strategy to facilitate molecular recognition by extending electron catalysis17, which is widely applied18-21 in synthetic covalent chemistry, into the realm of supramolecular non-covalent chemistry. As a proof of principle, we show that the formation of a trisradical complex22 between a macrocyclic host and a dumbbell-shaped guest-a molecular recognition process that is kinetically forbidden under ambient conditions-can be accelerated substantially on the addition of catalytic amounts of a chemical electron source. It is, therefore, electrochemically possible to control23 the molecular recognition temporally and produce a nearly arbitrary molar ratio between the substrates and complexes ranging between zero and the equilibrium value. Such kinetically stable supramolecular systems24 are difficult to obtain precisely by other means. The use of the electron as a catalyst in molecular recognition will inspire chemists and biologists to explore strategies that can be used to fine-tune non-covalent events, control assembly at different length scales25-27 and ultimately create new forms of complex matter28-30.

Harvesting electrons and holes from photodriven symmetry-breaking charge separation within a perylenediimide photosynthetic model dimer.

Understanding how to utilize symmetry-breaking charge separation (SB-CS) offers a path toward increasingly efficient light-harvesting technologies. This process plays a central role in the first step of photosynthesis, in which the dimeric "special pair" of the photosynthetic reaction center enters a coherent SB-CS state after photoexcitation. Previous research on SB-CS in both biological and synthetic chromophore dimers has focused on increasing the efficiency of light-driven processes. In a chromophore dimer undergoing SB-CS, the energy of the radical ion pair product is nearly isoenergetic with that of the lowest excited singlet (S1) state of the dimer. This means that very little energy is lost from the absorbed photon. In principle, the relatively high energy electron and hole generated by SB-CS within the chromophore dimer can each be transferred to adjacent charge acceptors to extend the lifetime of the electron-hole pair, which can increase the efficiency of solar energy conversion. To investigate this possibility, we have designed a bis-perylenediimide cyclophane (mPDI2) covalently linked to a secondary electron donor, peri-xanthenoxanthene (PXX) and a secondary electron acceptor, partially fluorinated naphthalenediimide (FNDI). Upon selective photoexcitation of mPDI2, transient absorption spectroscopy shows that mPDI2 undergoes SB-CS, followed by two secondary charge transfer reactions to generate a PXX•+-mPDI2-FNDI•- radical ion pair having a nearly 3 µs lifetime. This strategy has the potential to increase the efficiency of molecular systems for artificial photosynthesis and photovoltaics.

Syntheses of three-dimensional catenanes under kinetic control.

Although catenanes comprising two ring-shaped components can be made in large quantities by templation, the preparation of three-dimensional (3D) catenanes with cage-shaped components is still in its infancy. Here, we report the design and syntheses of two 3D catenanes by a sequence of SN2 reactions in one pot. The resulting triply mechanically interlocked molecules were fully characterized in both the solution and solid states. Mechanistic studies have revealed that a suit[3]ane, which contains a threefold symmetric cage component as the suit and a tribromide component as the body, is formed at elevated temperatures. This suit[3]ane was identified as the key reactive intermediate for the selective formation of the two 3D catenanes which do not represent thermodynamic minima. We foresee a future in which this particular synthetic strategy guides the rational design and production of mechanically interlocked molecules under kinetic control.

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.

Long-Lived Charge Separation in Single Crystals of an Electron Donor Covalently Linked to Four Acceptor Molecules.

Crystalline donor-acceptor (D-A) systems serve as an excellent platform for studying CT exciton creation, migration, and dissociation into free charge carriers for solar energy conversion. Donor-acceptor cocrystals have been utilized to develop an understanding of CT exciton formation in ordered organic solids; however, the strong electronic coupling of the D and A units can sometimes limit charge separation lifetimes due to their close proximity. Covalent D-A systems that preorganize specific donor-acceptor structures can assist in engineering crystal morphologies that promote long-lived charge separation to overcome this limitation. Here we investigate photogenerated CT exciton formation in a single crystal of a 2,5,8,11-tetraphenylperylene (PerPh4) donor to which four identical naphthalene-(1,4:5,8)-bis(dicarboximide) (NDI) electron acceptors are covalently attached at the para positions of the PerPh4 phenyl groups to yield PerPh4-NDI4. X-ray crystallography shows that the four NDIs pack pairwise into two distinct motifs. Two NDI acceptors of one PerPh4-NDI4 are positioned over the PerPh4 donors of adjacent PerPh4-NDI4 molecules with the donor and acceptor π-systems having a large dihedral angle between them, while the other two NDIs of PerPh4-NDI4 form xylene-NDI van der Waals π-stacks with the corresponding NDIs in adjacent PerPh4-NDI4 molecules. Upon selective photoexcitation of PerPh4 in the single crystal, CT exciton formation occurs in <300 fs yielding electron-hole pairs that live for more than ∼16 µs. This demonstrates the effectiveness of covalently linked D-A systems for engineering single crystal structures that promote efficient and long-lived charge separation for solar energy conversion.

Aberrant expansion of spontaneous splenic germinal centers induced by hallmark genetic lesions of aggressive lymphoma.

Unique molecular vulnerabilities have been identified in the aggressive MCD/C5 genetic subclass of diffuse large B-cell lymphoma (DLBCL). However, the premalignant cell-of-origin exhibiting MCD-like dependencies remains elusive. In this study, we examined animals carrying up to 4 hallmark genetic lesions found in MCD consisting of gain-of-function mutations in Myd88 and Cd79b, loss of Prdm1, and overexpression of BCL2. We discovered that expression of combinations of these alleles in vivo promoted a cell-intrinsic accumulation of B cells in spontaneous splenic germinal centers (GCs). As with MCD, these premalignant B cells were enriched for B-cell receptors (BCRs) with evidence of self-reactivity, displayed a de novo dependence on Tlr9, and were more sensitive to inhibition of Bruton's tyrosine kinase. Mutant spontaneous splenic GC B cells (GCB) showed increased proliferation and IRF4 expression. Mice carrying all 4 genetic lesions showed a >50-fold expansion of spontaneous splenic GCs exhibiting aberrant histologic features with a dark zone immunophenotype and went on to develop DLBCL in the spleen with age. Thus, by combining multiple hallmark genetic alterations associated with MCD, our study identifies aberrant spontaneous splenic GCBs as a likely cell-of-origin for this aggressive genetic subtype of lymphoma.

Ultrafast Charge Transfer Dynamics in a Slip-Stacked Donor-Acceptor-Acceptor System.

Photoexcitation of molecular electron donor and/or acceptor chromophore aggregates can greatly affect their charge-transfer dynamics. Excitonic coupling not only alters the energy landscape in the excited state but may also open new photophysical pathways, such as symmetry-breaking charge separation (SB-CS). Here, we investigate the impact of excitonic coupling on a covalent donor-acceptor-acceptor system comprising a perylene donor (Per) and two perylenediimide (PDI) acceptor chromophores in which the three components are π-stacked in a geometry that is slipped along their long axes (Per-PDI2). Following selective photoexcitation of PDI, femtosecond transient absorption data for Per-PDI2 is compared to that for the single-donor, single-acceptor Per-PDI system, and the PDI2 dimer, which both have the same interchromophore geometry as Per-PDI2. The data show that electron transfer from Per to the lower exciton state of the PDI dimer is slower than that of the single PDI acceptor system. This is due to the lower free energy of the reaction for charge separation because of the electronic stabilization afforded by the excitonic coupling between the PDIs. While PDI2 was shown previously to undergo ultrafast SB-CS, the strong π-π electronic interaction of Per with the adjacent PDI in Per-PDI2 breaks the electronic symmetry of the PDI dimer, resulting in the oxidation of Per rather than SB-CS. These results show that the electronic coupling between molecules designed to accept charges produced by SB-CS in molecular dimers and the chromophores comprising the dimer must be balanced to favor SB-CS.

A multiprotein supercomplex controlling oncogenic signalling in lymphoma.

B cell receptor (BCR) signalling has emerged as a therapeutic target in B cell lymphomas, but inhibiting this pathway in diffuse large B cell lymphoma (DLBCL) has benefited only a subset of patients1. Gene expression profiling identified two major subtypes of DLBCL, known as germinal centre B cell-like and activated B cell-like (ABC)2,3, that show poor outcomes after immunochemotherapy in ABC. Autoantigens drive BCR-dependent activation of NF-κB in ABC DLBCL through a kinase signalling cascade of SYK, BTK and PKCß to promote the assembly of the CARD11-BCL10-MALT1 adaptor complex, which recruits and activates IκB kinase4-6. Genome sequencing revealed gain-of-function mutations that target the CD79A and CD79B BCR subunits and the Toll-like receptor signalling adaptor MYD885,7, with MYD88(L265P) being the most prevalent isoform. In a clinical trial, the BTK inhibitor ibrutinib produced responses in 37% of cases of ABC1. The most striking response rate (80%) was observed in tumours with both CD79B and MYD88(L265P) mutations, but how these mutations cooperate to promote dependence on BCR signalling remains unclear. Here we used genome-wide CRISPR-Cas9 screening and functional proteomics to determine the molecular basis of exceptional clinical responses to ibrutinib. We discovered a new mode of oncogenic BCR signalling in ibrutinib-responsive cell lines and biopsies, coordinated by a multiprotein supercomplex formed by MYD88, TLR9 and the BCR (hereafter termed the My-T-BCR supercomplex). The My-T-BCR supercomplex co-localizes with mTOR on endolysosomes, where it drives pro-survival NF-κB and mTOR signalling. Inhibitors of BCR and mTOR signalling cooperatively decreased the formation and function of the My-T-BCR supercomplex, providing mechanistic insight into their synergistic toxicity for My-T-BCR+ DLBCL cells. My-T-BCR supercomplexes characterized ibrutinib-responsive malignancies and distinguished ibrutinib responders from non-responders. Our data provide a framework for the rational design of oncogenic signalling inhibitors in molecularly defined subsets of DLBCL.

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.

Coherent Vibronic Wavepackets Show Structure-Directed Charge Flow in Host-Guest Donor-Acceptor Complexes.

Designing and controlling charge transfer (CT) pathways in organic semiconductors are important for solar energy applications. To be useful, a photogenerated, Coulombically bound CT exciton must further separate into free charge carriers; direct observations of the detailed CT relaxation pathways, however, are lacking. Here, photoinduced CT and relaxation dynamics in three host-guest complexes, where a perylene (Per) electron donor guest is incorporated into two symmetric and one asymmetric extended viologen cyclophane acceptor hosts, are presented. The central ring in the extended viologen is either p-phenylene (ExV2+) or electron-rich 2,5-dimethoxy-p-phenylene (ExMeOV2+), resulting in two symmetric cyclophanes with unsubstituted or methoxy-substituted central rings, ExBox4+ and ExMeOBox4+, respectively, and an asymmetric cyclophane with one of the central viologen rings being methoxylated ExMeOVBox4+. Upon photoexcitation, the asymmetric host-guest ExMeOVBox4+ ⊃ Per complex exhibits directional CT toward the energetically unfavorable methoxylated side due to structural restrictions that facilitate strong interactions between the Per donor and the ExMeOV2+ side. The CT state relaxation pathways are probed using ultrafast optical spectroscopy by focusing on coherent vibronic wavepackets, which are used to identify CT relaxations along charge localization and vibronic decoherence coordinates. Specific low- and high-frequency nuclear motions are direct indicators of a delocalized CT state and the degree of CT character. Our results show that the CT pathway can be controlled by subtle chemical modifications of the acceptor host in addition to illustrating how coherent vibronic wavepackets can be used to probe the nature and time evolution of the CT states.

Quantum Sensing of Electric Fields Using Spin-Correlated Radical Ion Pairs.

Quantum sensing affords the possibility of using quantum entanglement to probe electromagnetic fields with exquisite sensitivity. In this work, we show that a photogenerated spin-correlated radical ion pair (SCRP) can be used to sense an electric field change created at one radical ion of the pair using molecular recognition. The SCRP is generated within a covalent donor-chromophore-acceptor system PXX-PMI-NDI, 1, where PXX = peri-xanthenoxanthene, PMI = 1,6-bis(p-t-butylphenoxy)perylene-3,4-dicarboximide, and NDI = naphthalene-1,8:4,5-bis(dicarboximide). The electron-rich PXX donor in 1 acts as a guest molecule that can be encapsulated selectively by a tetracationic cyclophane ExBox4+ host to give a supramolecular complex 1 ⊂ ExBox4+. Selective photoexcitation of the PMI chromophore results in ultrafast generation of the PXX•+-PMI-NDI•- SCRP. When PXX is encapsulated by ExBox4+, the cyclophane generates an electric field that repels the positive charge on PXX•+ within PXX•+-PMI-NDI•-, reducing the SCRP distance, i.e., the distance between the centers-of-charge on the donor and acceptor. Pulse-EPR measurements are used to measure the coherent oscillations created primarily by the electron-electron dipolar coupling in the SCRP, which yields the distance between the two charges (spins) of PXX•+-PMI-NDI•-. The experimental results show that the distance between PXX•+ and NDI•- decreases when ExBox4+ encapsulates PXX•+, which demonstrates that the SCRP can function as a quantum sensor to detect electric field changes in the vicinity of the radical ions.

Exciplex Emission and Förster Resonance Energy Transfer in Polycyclic Aromatic Hydrocarbon-Based Bischromophoric Cyclophanes and Homo[2]catenanes.

Energy transfer and exciplex emission are not only crucial photophysical processes in many living organisms but also important for the development of smart photonic materials. We report, herein, the rationally designed synthesis and characterization of two highly charged bischromophoric homo[2]catenanes and one cyclophane incorporating a combination of polycyclic aromatic hydrocarbons, i.e., anthracene, pyrene, and perylene, which are intrinsically capable of supporting energy transfer and exciplex formation. The possible coconformations of the homo[2]catenanes, on account of their dynamic behavior, have been probed by Density Functional Theory calculations. The unique photophysical properties of these exotic molecules have been explored by steady-state and time-resolved absorption and fluorescence spectroscopies. The tetracationic pyrene-perylene cyclophane system exhibits emission emanating from a highly efficient Förster resonance energy transfer (FRET) mechanism which occurs in 48 ps, while the octacationic homo[2]catenane displays a weak exciplex photoluminescence following extremely fast (<0.3 ps) exciplex formation. The in-depth fundamental understanding of these photophysical processes involved in the fluorescence of bischromophoric cyclophanes and homo[2]catenanes paves the way for their use in future bioapplications and photonic devices.

Divinylanthracene-Containing Tetracationic Organic Cyclophane with Near-Infrared Photoluminescence.

Near-infrared (NIR) light is known to have outstanding optical penetration in biological tissues and to be non-invasive to cells compared with visible light. These characteristics make NIR-specific light optimal for numerous biological applications, such as the sensing of biomolecules or in theranostics. Over the years, significant progress has been achieved in the synthesis of fluorescent cyclophanes for sensing, bioimaging, and making optoelectronic materials. The preparation of NIR-emissive porphyrin-free cyclophanes is, however, still challenging. In an attempt for fluorescence emissions to reach into the NIR spectral region, employing organic tetracationic cyclophanes, we have inserted two 9,10-divinylanthracene units between two of the pyridinium units in cyclobis(paraquat-p-phenylene). Steady-state absorption, fluorescence, and transient-absorption spectroscopies reveal the deep-red and NIR photoluminescence of this cyclophane. This tetracationic cyclophane is highly soluble in water and has been employed successfully as a probe for live-cell imaging in a breast cancer cell line (MCF-7).

Triplet-Triplet Annihilation Upconversion in a Porphyrinic Molecular Container.

Triplet-triplet annihilation-based molecular photon upconversion (TTA-UC) is a photophysical phenomenon that can yield high-energy emitting photons from low-energy incident light. TTA-UC is believed to fuse two triplet excitons into a singlet exciton through several consecutive energy-conversion processes. When organic aromatic dyes─i.e., sensitizers and annihilators─are used in TTA-UC, intermolecular distances, as well as relative orientations between the two chromophores, are important in an attempt to attain high upconversion efficiencies. Herein, we demonstrate a host-guest strategy─e.g., a cage-like molecular container incorporating two porphyrinic sensitizers and encapsulating two perylene emitters inside its cavity─to harness photon upconversion. Central to this design is tailoring the cavity size (9.6-10.4 Å) of the molecular container so that it can host two annihilators with a suitable [π···π] distance (3.2-3.5 Å). The formation of a complex with a host:guest ratio of 1:2 between a porphyrinic molecular container and perylene was confirmed by NMR spectroscopy, mass spectrometry, and isothermal titration calorimetry (ITC) as well as by DFT calculations. We have obtained TTA-UC yielding blue emission at 470 nm when the complex is excited with low-energy photons. This proof-of-concept demonstrates that TTA-UC can take place in one supermolecule by bringing together the sensitizers and annihilators. Our investigations open up some new opportunities for addressing several issues associated with supramolecular photon upconversion, such as sample concentrations, molecular aggregation, and penetration depths, which have relevance to biological imaging applications.

Two-Dimensional Electronic Spectroscopy Reveals Vibrational Modes Coupled to Charge Transfer in a Julolidine-BODIPY Dyad.

Understanding charge transfer (CT) dynamics in molecular donor-acceptor (D-A) dyads can provide insight into developing efficient D-A molecules for capturing solar energy. Here, we characterize the excited-state evolution of a julolidine-BODIPY (Jul-BD) D-A system with an emissive CT state using time-resolved fluorescence, femtosecond transient absorption, and two-dimensional electronic spectroscopies. Comparison of these results with those from phenyl-BODIPY (Ph-BD) allows us to identify the dynamics at play during CT state formation and its subsequent conversion to either a fully charge-separated or triplet state. Photoexcitation of Jul-BD in tetrahydrofuran results in the formation of an initial emissive CT state that relaxes before fully charge-separating. In contrast, Jul-BD in toluene exhibits similar CT state dynamics, albeit at slower timescales, before decaying to a terminal triplet species. Quantum beat analysis at early times in both solvents shows several vibronic modes, which are corroborated using density functional theory (DFT) calculations. For Ph-BD, a single 220 cm-1 compression mode about the single bond linking the phenyl to BODIPY modulates their orbital overlap. Three active vibronic modes, 147, 174, and 214 cm-1, are found in Jul-BD, regardless of the dielectric constant of the medium. These motions correspond to compression and torsional motions along the single bond joining Jul to BD and are responsible for the evolution of the spontaneous and stimulated emission features in the time-resolved spectroscopic data, which is further supported by time-dependent DFT calculations of the steady-state absorption spectrum of the Jul-BD as a function of increasing D-A dihedral core angle. These findings show how torsional and compression motions can play a pivotal role in intramolecular CT between a D and an A linked by a single bond.

Regulation of B cell receptor-dependent NF-κB signaling by the tumor suppressor KLHL14.

The KLHL14 gene acquires frequent inactivating mutations in mature B cell malignancies, especially in the MYD88L265P, CD79B mutant (MCD) genetic subtype of diffuse large B cell lymphoma (DLBCL), which relies on B cell receptor (BCR) signaling for survival. However, the pathogenic role of KLHL14 in DLBCL and its molecular function are largely unknown. Here, we report that KLHL14 is in close proximity to the BCR in the endoplasmic reticulum of MCD cell line models and promotes the turnover of immature glycoforms of BCR subunits, reducing total cellular BCR levels. Loss of KLHL14 confers relative resistance to the Bruton tyrosine kinase (BTK) inhibitor ibrutinib and promotes assembly of the MYD88-TLR9-BCR (My-T-BCR) supercomplex, which initiates prosurvival NF-κB activation. Consequently, KLHL14 inactivation allows MCD cells to maintain NF-κB signaling in the presence of ibrutinib. These findings reinforce the central role of My-T-BCR-dependent NF-κB signaling in MCD DLBCL and suggest that the genetic status of KLHL14 should be considered in clinical trials testing inhibitors of BTK and BCR signaling mediators in DLBCL.

Pathogenic B-cell receptor signaling in lymphoid malignancies: New insights to improve treatment.

Signals emanating from the B-cell receptor (BCR) promote proliferation and survival in diverse forms of B-cell lymphoma. Precision medicine strategies targeting the BCR pathway have been generally effective in treating lymphoma, but often fail to produce durable responses in diffuse large B-cell lymphoma (DLBCL), a common and aggressive cancer. New insights into DLBCL biology garnered from genomic analyses and functional proteogenomic studies have identified novel modes of BCR signaling in this disease. Herein, we describe the distinct roles of antigen-dependent and antigen-independent BCR signaling in different subtypes of DLBCL. We highlight mechanisms by which the BCR cooperates with TLR9 and mutant isoforms of MYD88 to drive sustained NF-κB activity in the activated B-cell-like (ABC) subtype of DLBCL. Finally, we discuss progress in detecting and targeting oncogenic BCR signaling to improve the survival of patients with lymphoma.

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.

π-Stacking-Dependent Vibronic Couplings Drive Excited-State Dynamics in Perylenediimide Assemblies.

Vibronic coupling, the interplay of electronic and nuclear vibrational motion, is considered a critical mechanism in photoinduced reactions such as energy transfer, charge transfer, and singlet fission. However, our understanding of how particular vibronic couplings impact excited-state dynamics is lacking due to the limited number of experimental studies of model molecular systems. Herein, we use two-dimensional electronic spectroscopy (2DES) to launch and interrogate a range of vibronic coherences in two distinct types of perylenediimide slip stacks─along the short and long molecular axes, which form either an excimer or a mixed state between the Frenkel exciton (FE) and charge transfer states. We explore the functionality of these vibronic coherences using quantum beatmaps, which display the Fourier amplitude signal oscillations as a function of pump and probe frequencies, along with knowledge of the characteristic signatures of the FE, ionic, and excimer species. We find that a low-frequency vibrational mode of the short-axis slip stack appears concomitantly with the formation of the excimer state, survives 2-fold longer than in the FE state in the reference monomer, and shows a phase shift compared to other modes. For the long-axis slip stacks, a pair of low-frequency modes coupled to a high-frequency coordinate of the FE state were found to play a critical role in mixed-state generation. Our findings thus experimentally reveal the complex and varying roles of vibronic couplings in tightly packed multimers undergoing a range of photoinduced processes.