Accelerating Intersystem Crossing in Multiresonance Thermally Activated Delayed Fluorescence Emitters via Long-Range Charge Transfer.

Multiresonance thermally activated delayed fluorescence (MR-TADF) emitters are excellent candidates for high-performance organic light-emitting diodes (OLEDs) due to their narrowband emission properties. However, the inherent mechanism of regulating the rate of intersystem crossing (ISC) is ambiguous in certain MR-TADF skeletons. Herein, we propose a mechanism of accelerating ISC in B/S-based MR-TADF emitters by peripheral modifications of electron-donating groups (EDGs) without affecting the narrowband emission property. The long-range charge transfer (LRCT) stems from the introduced EDG leading to high-lying singlet and triplet excited states. The ISC process is accelerated by the enhanced spin-orbital coupling (SOC) between the singlet short-range charge transfer (SRCT) and triplet LRCT manifolds. Meanwhile, the narrowband emission derived from the MR-type SRCT state is well retained as expected in the peripherally modified MR-TADF emitters. This work reveals the regulation mechanism of photophysical properties by high-lying LRCT excited states and provides a significant theoretical basis for modulating the rate of ISC in the further design of MR-TADF materials.

Theoretical Study on the Reaction between Carcinogenic 2,5-Dichloro-1,4-benzoquinone and tert-Butyl Hydroperoxide: Self-Catalysis and Water Catalysis.

The potentially carcinogenic halobenzoquinones (HBQs) have been recently identified in drinking water as disinfection byproducts. Several radical intermediates in the reaction of 2,5-dichloro-1,4-benzoquinone (DCBQ) and t-butyl hydroperoxide (t-BuOOH), which may induce DNA damage, were detected experimentally, and metal-independent decomposition reactions of t-BuOOH by DCBQ were proposed. It has not yet been confirmed by theoretical calculations. The theoretical study in this work provides insights into the details of the reaction. An unprecedented self-catalysis mechanism of organic hydroperoxides, that is, the reactant t-BuOOH also has a catalytic effect, was uncovered at the molecular level. Moreover, as the solvent, water molecules also clearly have an efficient catalytic effect. Due to the catalysis of t-BuOOH and water, the metal-independent reaction of t-BuOOH and DCBQ can occur under moderate conditions. Our findings about the novel catalytic effect of organic hydroperoxides t-BuOOH could offer a unique perspective into the design of new catalysts and an understanding of the catalytic biological, environmental, and air pollution reactions. Furthermore, organic hydroperoxide t-BuOOH could serve as a proton shuttle, where the proton transfer process is accompanied by simultaneous charge transfer. Therefore, organic hydroperoxides may disrupt the vital proton transfer process in biological systems and may give rise to unexpected toxicity.

Excimer Formation Driven by Excited-State Structural Relaxation in a Covalent Aminonaphthalimide Dimer.

Strongly coupled excimer formation from interchromophoric charge transfer driven by the ultrafast excited-state structural dynamics of a 5,5'-linked 4-amino-1,8-naphthalimide covalent homodimer was investigated by ultrafast transient spectroscopy and chemical calculations. Theoretical calculations indicate that the structural relaxation associated with the dihedral motion leads to significantly enhanced interchromophoric charge transfer (CT) coupling, which favors the formation of an excimer-like symmetry-broken CT state. The formation and relaxation dynamics of the excimer state in the dimer are identified via ultrafast transient absorption and fluorescence spectroscopy. The structural relaxation following the photoexcitation occurs in tens of picoseconds and stabilizes the dimer to the strongly coupled excimer state. The highly polar solvents further stabilize the excimer state and enhance the CT character, which enable efficient electron and excitation energy transport in covalent molecular aggregates.

Exploring Solvent Polarity-Dependent Photocatalysis Mechanism of Organic Photoredox Catalysts.

Organic dyads with intramolecular charge-transfer (ICT) character are emerging as viable and more sustainable photocatalysts than metal-based complexes. Herein, a carbazole- and naphthalimide-based organic dyad (Cz-NI) was designed as an efficient organic photocatalyst for the direct C(sp3)-H carbamoylation of saturated aza-heterocycles. Aiming at understanding the effect of environment, especially the solvent polarity on photocatalysis performance, the excited-state dynamics of Cz-NI in different polar solvents were studied by femtosecond (fs) and nanosecond (ns) time-resolved transient absorption (TA) spectroscopy. Fs-TA measurements indicate that the formation of an intramolecular charge separation (ICS) state with twisted structural feature in polar solvents is driven and stabilized by solvation dynamics. Combined with chemical calculations, we found that orbital decoupling, poor conjugation between Cz and NI groups due to intramolecular torsional motion and transition moments associated with ICT emission, limits excited-state deactivation through radiation and nonradiation transition to the ground state. In addition, the orthogonal π-system of the ICS state enables the efficient spin-orbit, charge-transfer intersystem crossing to a triplet state, which is localized on the NI group. Spectroscopic and computational results reveal the formation of an ICS state at an appropriate energy that enables the population of the triplet state with high quantum yield, and the localized triplet state has long lifetime and high reduction potential for subsequent reactions. Therefore, solvent-solute interaction, especially the solvation-coupled excited-state structural relaxation, is the main factor that the photocatalysis efficiency of Cz-NI has a significant polarity correlation.

Unveiling Solvation Dynamics of Excited and Ground States via Ultrafast Pump-Dump-Probe Spectroscopy.

The conventional ultrafast pump-probe spectroscopy has primarily focused on examining the formation and decay of the excited state intermediates, but it is very difficult to detect those intermediates while the formation is slow and dissipation is much fast because of the limited concentration during the intrinsic photocycle. To address this issue, a multipulse ultrafast pump-dump-probe spectroscopy was employed to generate and probe the short-lived ground state intermediates (GSIs) in an electronic push-pull pyrene derivative (EPP). This particular derivative undergoes planarized intramolecular charge transfer (PICT) in the excited state upon initial femtosecond pulse excitation. After applying the dump pulse once the PICT was formed, the blue-shifted transient absorption GSIs with the ground state dynamics of the structure recovery was directly observed. It is found that GSIs undergo slower reorganization than the PICT formation in the excited state of EPP due to the solvation effect with different dipole moments of ground states and excited states. These findings provide a comprehensive understanding of the full photocycle dynamics of both the ground and excited states, shedding light on the presence of hidden ground state behaviors.

Intrinsic Photostability in Dithiolonaphthalimide Achieved by Disulfide Bond-Induced Excited-State Quenching.

Disulfide bridges common in proteins show excellent photostability achieved by ultrafast internal conversion and maintain the stability of the tertiary structure. When disulfide bonds exist in aromatic compounds, the rigid chemical structure may affect the cleavage and reforming dynamics of disulfide bonds. In this work, a model compound with a disulfide five-membered-ring structure, 4,5-dithiolo-N-(2,6-dimethylphenyl)-1,8-naphthalimide (DTDPNI), is selected to elaborate the effect of disulfide modification on the excited-state deactivation mechanism. Quantum chemical calculations show that the S-S stretching leads to a dramatic decrease in the energy gap between the S1 and S0 states, similar to the situation in 1,2-dithiane. Due to the efficient nonradiative process, the excited-state lifetime of DTDPNI resolved by ultrafast spectroscopy is determined to be ∼20 ps. It is found that the excellent photostability is achieved by ultrafast excited-state quenching induced by the S-S stretching, rather than the cleavage of the disulfide bond; even the disulfide bridge is in a very rigid aromatic molecular system.

Spin-orbit charge-transfer intersystem crossing in heavy-atom-free orthogonal covalent boron-dipyrromethene heterodimers.

Boron-dipyrromethene (BODIPY) derivatives are prospective organic-based triplet photosensitizers. Since the triplet generation yield of the parent BODIPY is low, heavy atoms are widely used to improve the triplet yield. However, the dimerization of BODIPYs can also significantly improve their ability to produce triplets. Through a comparative study of the triplet formation dynamics of two heavy-atom-free orthogonal covalent BODIPY heterodimers that differ in their dihedral angles, we have demonstrated that the mechanism of spin-orbit charge-transfer intersystem crossing (SOCT-ISC) promotes the triplet generation of BODIPY heterodimers in solution. Different from the general understanding of SOCT-ISC, the heterodimer with a smaller dihedral angle and low structural rigidity showed better triplet generation due to (a) the stronger inter-chromophoric interaction in the heterodimer, which promoted the formation of a solvent-stabilized charge-transfer (CT) state, (b) the more favorable energy level alignment with sizeable spin-orbit coupling strength, and (c) the balance between the stabilized singlet CT state and limited direct charge recombination to the ground state in a weakly polar solvent. The complete spectral characterization of the triplet formation dynamics clarified the SOCT-ISC mechanism and important factors affecting the triplet generation in BODIPY heterodimers.

Correlation analysis of lung mucosa-colonizing bacteria with clinical features reveals metastasis-associated bacterial community structure in non-small cell lung cancer patients.

BACKGROUND: Microbes colonizing lower airways can regulate the host immune profile and consequently participate in lung disease. Increasing evidence indicate that individual microbes promote lung cancer progression and are involved in metastasis incidence. To date, however, no study has revealed the community structure of lung bacteria in metastatic non-small cell lung cancer (NSCLC) patients. METHODS: We prospectively enrolled 50 healthy subjects and 57 NSCLC patients. All healthy subjects and NSCLC patients underwent bronchoscope procedures for brush specimen collection. The 16 S ribosomal RNA gene was sequenced to characterize the community structure of lung mucosa-colonizing bacteria. The peripheral blood of NSCLC patients was also measured for leukocytes and cancer markers. RESULTS: The lung bacteria of healthy subjects and NSCLC patients were divided into four communities. All community 2 members showed increased abundance in NSCLC patients compared with healthy subjects, and most community 2 members showed increased abundance in the metastatic NSCLC patients compared with the non-metastatic group. These bacteria were significantly and positively correlated with eosinophils, neutrophils and monocytes in the metastatic NSCLC group. In addition, the correlation between lung bacteria and cancer markers differed between the metastatic and non-metastatic NSCLC patients. Furthermore, bronchoalveolar lavage fluid from lung adenocarcinoma patients directly promoted NSCLC cell migration. CONCLUSIONS: The community structure of lung mucosa-colonizing bacteria was relatively stable, but changed from the healthy population to NSCLC patients, especially the metastatic group. This distinct community structure and specific correlation with immune cells and cancer markers could help to distinguish NSCLC patients with or without metastasis.

Ultrafast Charge Separation Driven by Torsional Motion in Orthogonal Boron Dipyrromethene Dimer.

In this work, the photoinduced charge separation (CS) via symmetry breaking in an orthogonal meso-ß-linked boron dipyrromethene (BODIPY) dimer was investigated by polarized transient absorption spectroscopy. The time constant about 0.76 ps of the CS reaction determined in dimethyl sulfoxide is much faster than the solvation dynamics. The observed transient anisotropy of the BODIPY anion band implies that both hole and electron transfers occur with similar probabilities. The bidirectional charge transfer processes suggest that the locally excited state is weakly coupled to the polar solvent, and the solvation coupled excited-state structural relaxation within the BODIPY monomeric unit is rather limited. In combination with the electronic excitation analysis based on time-dependent density-functional theory calculations, we deduced that the CS in the orthogonal BODIPY dimer is enabled via the torsional motion associated with covalently connected BODIPY units, promoting the electronic coupling, and irrelevant to the dynamic solvent relaxation.

Symmetry-breaking charge separation in a nitrogen-bridged naphthalene monoimide dimer.

The photophysical properties of 4-aminonaphthalene-1,8-imide-based derivatives, bis-ANI, consisting of two naphthalimide (NI) units linked by a butylamine bridge and its monomer ANI have been intensively investigated by steady-state and transient spectroscopy combined with quantum chemical calculations. The excited state relaxation dynamics of the two molecules are studied in three solvents of varying polarity - from hexane to tetrahydrofuran to acetone. A strong reduction in the fluorescence quantum yields and larger red shifts of the emission spectra are observed when going from the monomer ANI to dimer bis-ANI with increasing solvent polarity. It is found that the presence of the central amino linker in bis-ANI facilitates the formation of an asymmetric CS state between the ANI and NI moieties in bis-ANI, where NI˙- is the dominant radical anion unit after CS, evidenced by the femtosecond transient absorption measurements and spectroelectrochemistry in polar solvents. Femtosecond transient absorption spectra and quantum chemical calculations reveal the conformational change after the formation of the symmetry-breaking charge separation (SBCS) state upon photoexcitation, while a near-orthogonal structure in the excited state of bis-ANI retards charge recombination. In addition, it is evidenced that the rate of SBCS can be tuned by changing the different polar solvents.

Correlation between Excited-State Intramolecular Proton Transfer and Electron Population on Proton Donor/Acceptor in 2-(2'-Hydroxyphenyl)oxazole Derivatives.

Modulating the excited-state intramolecular proton transfer (ESIPT) reaction to achieve anticipant performance is always fascinating for chemists. However, feasible methods and a definite mechanism for tuning the ESIPT reaction remain insufficient. In this work, we reported the feasibility of continuously modulating the ESIPT dynamics in 2-(2'-hydroxyphenyl)oxazole (HPO) derivatives with different substitutions on the positions 5 and 5' of the core HPO through steady-state/transient spectroscopy and theoretical calculations. We found that the main factor affecting the tendency of the ESIPT reaction is the variation of electron population on proton donor and acceptor. An index Δpdif was proposed to evaluate the overall promotion effect on proton transfer caused by the variation of electron population on proton donor and acceptor, which shows high reliability in interpreting the ESIPT tendency. This method, for its capacity to quickly estimate the tendency of ESIPT, shows great potential in ESIPT molecular design with chemical substitution of electron-donating/withdrawing moieties.

Conformation-related excited-state charge transfer/separation of donor-π-acceptor chromophores.

Understanding the excited-state charge transfer/separation (CT/CS) of donor-π-acceptor chromophores can provide guidance for designing and synthesizing advanced dyes to improve the performance of dye-sensitized solar cells (DSSCs) in practical applications. Herein, two newly synthesized electronic push-pull molecules, CS-14 and CS-15, that consist of carbazole donor and benzothiadiazole acceptor segments are chosen to explore the ultrafast dynamics of intramolecular CT/CS processes. The theoretical calculation results depict an excited-state intramolecular CT character for both dyes, while the dihedral angle between donor and acceptor of CS-14 is larger than that of CS-15, suggesting a more significant CT character of CS-14. Furthermore, compared to CS-14, the bond rotation of CS-15 between donor and π-bridge is restricted by employing the hexatomic ring, indicating the stronger molecular planarization of CS-15. Ultrafast spectroscopy clearly shows a solvent polarity-dependent excited-state species evolution from CT to CS-the CT character is observed in low-polar toluene solvent, while the feature of the CS state in polar tetrahydrofuran and acetone solvents is captured, which successfully proved a solvent polarity modulated excited-state CT/CS characters. We also found that though the generation of the CS state within CS-14 is slightly faster than that of CS-15, the charge recombination process of CS-15 with excellent planar conformation is much slower, providing enough time for a higher charge migration efficiency in DSSCs.

Rational Design of Dot-on-Rod Nano-Heterostructure for Photocatalytic CO2 Reduction: Pivotal Role of Hole Transfer and Utilization.

Inspired by green plants, artificial photosynthesis has become one of the most attractive approaches toward carbon dioxide (CO2 ) valorization. Semiconductor quantum dots (QDs) or dot-in-rod (DIR) nano-heterostructures have gained substantial research interest in multielectron photoredox reactions. However, fast electron-hole recombination or sluggish hole transfer and utilization remains unsatisfactory for their potential applications. Here, the first application of a well-designed ZnSe/CdS dot-on-rods (DORs) nano-heterostructure for efficient and selective CO2 photoreduction with H2 O as an electron donor is presented. In-depth spectroscopic studies reveal that surface-anchored ZnSe QDs not only assist ultrafast (≈2 ps) electron and hole separation, but also promote interfacial hole transfer participating in oxidative half-reactions. Surface photovoltage (SPV) spectroscopy provides a direct image of spatially separated electrons in CdS and holes in ZnSe. Therefore, ZnSe/CdS DORs photocatalyze CO2 to CO with a rate of ≈11.3 µmol g-1 h-1 and ≥85% selectivity, much higher than that of ZnSe/CdS DIRs or pristine CdS nanorods under identical conditions. Obviously, favored energy-level alignment and unique morphology balance the utilization of electrons and holes in this nano-heterostructure, thus enhancing the performance of artificial photosynthetic solar-to-chemical conversion.

Bridge-Length- and Solvent-Dependent Charge Separation and Recombination Processes in Donor-Bridge-Acceptor Molecules.

The photoinduced intramolecular charge separation (CS) and charge recombination (CR) phenomena in a series of donor-bridge-acceptor (D-B-A) molecules are intensively investigated as a means of understanding electron transport through the π-B. Pyrene (Pyr) and triarylamine (TAA) moieties connected via phenylene Bs of various lengths are studied because their CS and CR behaviors can be readily monitored in real time by femtosecond transient absorption (fs-TA) spectroscopy. By combining the steady-state and fs-TA spectroscopic measurements in a variety of solvents together with chemical calculations, the parameters that govern the CS behaviors of these dyads were obtained, such as the solvent effects on free energy and the B-length-dependent electronic coupling (VDA) between D and A. We observed the sharp switch of the CS behavior with the increase of the solvent polarity and B-linker lengths. Furthermore, in the case of the shortest distance between D and A when the electron coupling is sufficiently large, we observed that the CS phenomenon occurs even in low-polar solvents. Upon increasing the length of B, CS occurs only in strong polar solvents. The distance-dependent decay constant of the CS rate is determined as ∼0.53 Å-1, indicating that CS is governed by superexchange tunneling interactions. The CS rate constants are also approximately estimated using Marcus electron transfer theory, and the results imply that the VDA value is the key factor dominating the CS rate, while the facile rotation of the phenylene B is important for modulating the lifetime of the charge-separated state in these D-B-A dyads. These results shed light on the practical strategy for obtaining a high CS efficiency with a long-lived CS state in TAA-B-Pyr derivatives.

Solvent Effect on Excited-State Intramolecular Proton-Coupled Charge Transfer Reaction in Two Seven-Membered Ring Pyrrole-Indole Hydrogen Bond Systems.

In the past decades, tremendous efforts have been invested into organic molecules involved in the excited-state intramolecular proton transfer (ESIPT) reaction due to their enormously Stokes-shifted fluorescence and distinctive photophysical properties. The alterations of the environmental medium can effectively adjust the luminous performance of ESIPT molecules, which inspires us to unravel the solvent effect on the ESIPT mechanism. Here, we report the solvent-dependent excited-state properties of two new seven-membered ring pyrrole-indole ESIPT molecules, g-PPDBI and e-PPDBI, by steady-state spectra, picosecond transient fluorescence spectra, femtosecond transient absorption spectra, and theoretical calculations. The bathochromic-shifted normal fluorescence and the negligibly shifted tautomer fluorescence suggest the occurrence of an excited-state intramolecular proton-coupled charge transfer reaction. Thus, the solvent effect plays a vital role in stabilizing the intramolecular charge transferred state, resulting in a higher ESIPT reaction barrier in more polar solvents. Additionally, the observation of the slight dynamic difference between PPDBIs with different π-conjugation positions provides a new strategy to adjust the performance of ESIPT molecules.

Delocalized Excitation or Intramolecular Energy Transfer in Pyrene Core Dendrimers.

Light-harvesting and then intramolecular energy transfer are the crucial steps in natural photosynthesis. Dendrimers are one of the most promising artificial light-harvesting antennas. Insight into the relationship between molecular structure and energy transfer (or delocalized excitation) in dendrimers would help in understanding and mimicking photosynthesis. Here, a series of dendrimers T1-T4 based on pyrene as a core and fluorene/carbazole as the dendrons have been studied with time-resolved fluorescence and femtosecond transient absorption spectroscopies, revealing that the large planar structure of T1 and T2 has led to strong coupling of pyrene and fluorene units, enabling delocalized excitation over the entire molecules. But for T3 and T4, the carbazole units linking the first- and second-generation branches have broken the planar structure and suppressed the π-electron delocalization, enabling the Förster resonance energy transfer. The efficient intramolecular energy transfer from peripheral branches to the core occurs within 2 ps.

Direct Tracking Excited-State Intramolecular Charge Redistribution of Acceptor-Donor-Acceptor Molecule by Means of Femtosecond Stimulated Raman Spectroscopy.

Symmetric quadrupolar molecules generally exhibit apolar ground states and dipolar excited states in a polar environment, which is explained by the excited state evolution from initial charge delocalization over all molecules to localization on one branch of the molecules after a femtosecond pulse excitation. However, direct observation of excited-state charge redistribution (delocalization/localization) is hardly accessible. Here, the intramolecular charge delocalization/localization character of a newly synthesized acceptor-donor-acceptor molecule (ADA) has been intensively investigated by femtosecond stimulated Raman scattering (FSRS) together with femtosecond transient absorption (fs-TA) spectroscopy. By tracking the excited state Raman spectra of the specific alkynyl (-C≡C-) bonds at each branch of ADA, we found that the nature of the relaxed S1 state is strongly governed by solvent polarity: symmetric delocalized intramolecular charge transfer (ICT) characters occurred in apolar solvent, whereas the asymmetric localized ICT characters appeared in polar solvent because of solvation. The solvation dynamics of ADA extracted from fs-TA is consistent with the time constants obtained by FSRS, but the FSRS clearly tracks the excited state intramolecular charge transfer delocalization/localization.

Excited-State Symmetry-Breaking Charge Separation Dynamics in Multibranched Perylene Diimide Molecules.

As one of the most promising nonfullerene acceptors for organic photovoltaics, perylene diimide (PDI)-based multibranched molecules with twisted or three-dimensional (3D) geometric structures have been developed, which effectively increase the power conversion efficiency (PCE) of organic solar cells. Understanding the structure-property relationships in multichromophoric molecular architectures at molecular and ultrafast time levels is a crucial step in establishing new design principles in organic electronic materials. For this, photodriven excited-state symmetry-breaking charge separation (SB-CS) of PDI-based multichromophoric acceptors has been proposed to improve the PCE by reducing the self-aggregation of the planar PDI monomer. Herein, we investigated the intramolecular excited-state SB-CS and charge recombination (CR) dynamics of two symmetric phenyl-methane-based PDI derivatives, a twist dimer PM-PDI2 (phenyl-methane-based PDI dimer) and a 3D configuration tetramer PM-PDI4 (phenyl-methane-based PDI tetramer), in different solvents using ultrafast femtosecond transient absorption (fs-TA) spectroscopy and quantum chemical calculations. The quantum chemical calculations and steady-state spectra show that the two PDI derivatives undergo conformational changes upon excitation, leading to their emission states that have the characteristics of partial charge-transfer (CT) exciton in all solvents. Based on the evolution of the fs-TA data, it is observed that the evolution from the CT state to SB-CS state is disfavored in a weak polar solvent, whereas clear SB-CS spectroscopic signatures of cationic and anionic PDI are observed in polar solvents. Faster CS and slower CR processes of PM-PDI4 are observed in comparison to those of PM-PDI2. The crowded space in the 3D structure shortens the distance between the branches, leading to a stronger electronic coupling at the lowest excited state and a larger negative Gibbs free energy change of PM-PDI4 relative to that of PM-PDI2, which benefits the charge separation among PDI units in PM-PDI4. Besides, the 3D structure of PM-PDI4 also restricts rotation to a surface crossing region between the excited state and ground state, thus inhibiting nonradiative CR process and increasing the CS state lifetime. Our results suggest that the kinetics of CS and CR processes are strongly related to the molecular geometric structure, and the excited-state symmetry breaking in the 3D structure acceptor has superior photogenerated charge and photovoltaic properties from the perspective of ultrafast dynamics.

Electron-donating strength dependent symmetry breaking charge transfer dynamics of quadrupolar molecules.

The excited state symmetry breaking charge transfer (SBCT) dynamics of two diacetylide-triphenylamine (DATPA) derivatives with different electron-donating abilities are investigated by femtosecond transient absorption and fluorescence spectroscopy. By tracking the evolution of the excited states by transient absorption spectra and the kinetics of the instantaneous emission dipole moments obtained from transient fluorescence spectroscopy, it is found that, in nonpolar solvent, the relaxed S1 state is quadrupolar with little change of emission dipole moments for the two molecules within 30 ps, whereas in polar solvent, the quadrupolar state evolves to a symmetry broken S1 state, in which, the emission dipole moment exhibits a fast reduction in the first few picoseconds. The larger reduction in emission transition dipole moment for the molecule with stronger electron-donating methoxy groups indicates a larger extent of symmetry breaking compared with the one with weak electron-donating methyl groups. Consequently, we revealed that the magnitude of symmetry breaking can be tuned by changing the electron-donors in quadrupolar molecules.

Supramolecular Polymeric Radicals: Highly Promoted Formation and Stabilization of Naphthalenediimide Radical Anions.

The supramolecular polymeric radicals are developed to promote the generation efficiency and stability of naphthalenediimide (NDI) radical anions. To this end, a water-soluble bifunctional monomer bearing two naphthalene-viologen end groups and a NDI center is designed and synthesized. The supramolecular polymeric NDI radical anions are fabricated on the basis of host-guest complexation between the NDI-containing bifunctional monomer and cucurbit[8]uril (CB[8]) and followed by the photoinduced electron transfer process under UV light irradiation. The electrostatic effect of CB[8] and the bulky and rigid structure of supramolecular polymer are combined to stabilize the excited state of NDIs and NDI radical anions, contributing to the high enhancement of the formation of NDI radical anions with excellent stability. It is found that the highest occupied molecular orbital energy and lowest unoccupied molecular orbital energy of NDI are also lowered by the formation of supramolecular polymer. In addition, the supramolecular polymeric NDI radical anions could be utilized as a supramolecular photoreducing agent to reduce cytochrome C with a higher efficiency. It is anticipated that other radicals can also be stabilized through this strategy, and this line of research may lead to the development of novel polymeric radical materials.