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.

Response to Bruton's tyrosine kinase inhibitors in aggressive lymphomas linked to chronic selective autophagy.

Diffuse large B cell lymphoma (DLBCL) is an aggressive, profoundly heterogeneous cancer, presenting a challenge for precision medicine. Bruton's tyrosine kinase (BTK) inhibitors block B cell receptor (BCR) signaling and are particularly effective in certain molecular subtypes of DLBCL that rely on chronic active BCR signaling to promote oncogenic NF-κB. The MCD genetic subtype, which often acquires mutations in the BCR subunit, CD79B, and in the innate immune adapter, MYD88L265P, typically resists chemotherapy but responds exceptionally to BTK inhibitors. However, the underlying mechanisms of response to BTK inhibitors are poorly understood. Herein, we find a non-canonical form of chronic selective autophagy in MCD DLBCL that targets ubiquitinated MYD88L265P for degradation in a TBK1-dependent manner. MCD tumors acquire genetic and epigenetic alterations that attenuate this autophagic tumor suppressive pathway. In contrast, BTK inhibitors promote autophagic degradation of MYD88L265P, thus explaining their exceptional clinical benefit in MCD DLBCL.

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.

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.

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.

Direct observation of chirality-induced spin selectivity in electron donor-acceptor molecules.

The role of chirality in determining the spin dynamics of photoinduced electron transfer in donor-acceptor molecules remains an open question. Although chirality-induced spin selectivity (CISS) has been demonstrated in molecules bound to substrates, experimental information about whether this process influences spin dynamics in the molecules themselves is lacking. Here we used time-resolved electron paramagnetic resonance spectroscopy to show that CISS strongly influences the spin dynamics of isolated covalent donor-chiral bridge-acceptor (D-Bχ-A) molecules in which selective photoexcitation of D is followed by two rapid, sequential electron-transfer events to yield D•+-Bχ-A•-. Exploiting this phenomenon affords the possibility of using chiral molecular building blocks to control electron spin states in quantum information applications.

TLR9 ligand sequestration by chemokine CXCL4 negatively affects central B cell tolerance.

Central B cell tolerance is believed to be regulated by B cell receptor signaling induced by the recognition of self-antigens in immature B cells. Using humanized mice with defective MyD88, TLR7, or TLR9 expression, we demonstrate that TLR9/MYD88 are required for central B cell tolerance and the removal of developing autoreactive clones. We also show that CXCL4, a chemokine involved in systemic sclerosis (SSc), abrogates TLR9 function in B cells by sequestering TLR9 ligands away from the endosomal compartments where this receptor resides. The in vivo production of CXCL4 thereby impedes both TLR9 responses in B cells and the establishment of central B cell tolerance. We conclude that TLR9 plays an essential early tolerogenic function required for the establishment of central B cell tolerance and that correcting defective TLR9 function in B cells from SSc patients may represent a novel therapeutic strategy to restore B cell tolerance.

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.

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.

Targeting N-linked Glycosylation for the Therapy of Aggressive Lymphomas.

Diffuse large B-cell lymphoma (DLBCL) can be subdivided into the activated B-cell (ABC) and germinal center B cell-like (GCB) subtypes. Self-antigen engagement of B-cell receptors (BCR) in ABC tumors induces their clustering, thereby initiating chronic active signaling and activation of NF-κB and PI3 kinase. Constitutive BCR signaling is essential in some GCB tumors but primarily activates PI3 kinase. We devised genome-wide CRISPR-Cas9 screens to identify regulators of IRF4, a direct transcriptional target of NF-κB and an indicator of proximal BCR signaling in ABC DLBCL. Unexpectedly, inactivation of N-linked protein glycosylation by the oligosaccharyltransferase-B (OST-B) complex reduced IRF4 expression. OST-B inhibition of BCR glycosylation reduced BCR clustering and internalization while promoting its association with CD22, which attenuated PI3 kinase and NF-κB activation. By directly interfering with proximal BCR signaling, OST-B inactivation killed models of ABC and GCB DLBCL, supporting the development of selective OST-B inhibitors for the treatment of these aggressive cancers. SIGNIFICANCE: DLBCL depends on constitutive BCR activation and signaling. There are currently no therapeutics that target the BCR directly and attenuate its pathologic signaling. Here, we unraveled a therapeutically exploitable, OST-B-dependent glycosylation pathway that drives BCR organization and proximal BCR signaling. This article is highlighted in the In This Issue feature, p. 1749.

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.

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 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.

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.

Singlet Fission in Perylene Monoimide Single Crystals and Polycrystalline Films.

Singlet fission (SF) is a spin-allowed process in which a photogenerated singlet exciton down-converts into two triplet excitons. Perylene-3,4-dicarboximide (PMI) has singlet and triplet state energies of 2.4 and 1.1 eV, respectively; thus making SF slightly exoergic and providing triplet excitons that have sufficient energy to raise the efficiency of single-junction solar cells by reducing thermalization losses from hot excitons formed when absorbed photons have energies higher than the semiconductor bandgap. However, PMI SF in the solid state has not been studied previously. Here, we show that 2,5-diphenyl-N-(2-ethylhexyl)perylene-3,4-dicarboximide (dp-PMI) crystallizes into a slip-stacked intermolecular morphology favorable for SF. Transient absorption microscopy and spectroscopy show that dp-PMI SF occurs in ≤50 ps in both single crystals and polycrystalline thin films with a triplet yield of 150 ± 20%. Ultrafast SF in the solid state, the high triplet yield, and its photostability make dp-PMI an attractive candidate for SF-enhanced solar cells.

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.

Optical Initialization of Molecular Qubit Spin States Using Weak Exchange Coupling to Photogenerated Fullerene Triplet States.

The ability to initialize an electron spin qubit into a well-defined state is an important criterion for quantum information applications. To achieve this goal, a chromophore photoexcited to its triplet state is used to strongly spin polarize a nearby stable radical in a series of C60 fullerene derivatives containing a covalently linked α,γ-bisdiphenylene-ß-phenylallyl (BDPA) radical. Selective photoexcitation of C60 results in up to 20-fold enhancement of the BDPA spin polarization observed by pulse electron paramagnetic resonance spectroscopy at room temperature. The sign of the spin polarization depends on the nature of the molecular spacer between C60 and BDPA. In addition, transient absorption spectroscopy and pulse-EPR measurements reveal that the BDPA spin polarization is derived from spin polarization transfer from the C60 triplet state by weak exchange coupling over a 1 nm distance.

Thermally Controlled Exciplex Fluorescence in a Dynamic Homo[2]catenane.

Motion-induced change in emission (MICE) is a phenomenon that can be employed to develop various types of probes, including temperature and viscosity sensors. Although MICE, arising from the conformational motion in particular compounds, has been studied extensively, this phenomenon has not been investigated in depth in mechanically interlocked molecules (MIMs) undergoing coconformational changes. Herein, we report the investigation of a thermoresponsive dynamic homo[2]catenane incorporating pyrene units and displaying relative circumrotational motions of its cyclophanes as evidenced by variable-temperature 1H NMR spectroscopy and supported by its visualization through molecular dynamics simulations and quantum mechanics calculations. The relative coconformational motions induce a significant change in the fluorescence emission of the homo[2]catenane upon changes in temperature compared with its component cyclophanes. This variation in the exciplex emission of the homo[2]catenane is reversible as demonstrated by four complete cooling and heating cycles. This research opens up possibilities of using the coconformational changes in MIMs-based chromophores for probing fluctuations in temperature which could lead to applications in biomedicine or materials science.