Long-lived Charge-separated State Research Articles

Observation of Long-Lived Charge-Separated States in Anthraquinone-Phenothiazine Electron Donor-Acceptor Dyads: Transient Optical and Electron Paramagnetic Resonance Spectroscopic Studies.

We prepared a series of phenothiazine (PTZ)-anthraquinone (AQ) electron donor-acceptor dyads to study the relationship between molecular structures and the possibility of charge transfer (CT) and intersystem crossing (ISC). As compared to the previously reported PTZ-AQ dyad with a direct connection of two units via a C-N single bond, the PTZ and AQ units are connected via a p-phenylene or p-biphenylene linker. Conformation restriction is imposed by attaching ortho-methyl groups on the phenylene linker. UV-vis absorption spectra indicate electronic coupling between the PTZ and AQ units in the dyads without conformation restriction. Different from the previously reported PTZ-AQ, thermally activated delayed fluorescence (TADF) is observed for the dyads containing one phenylene linker (PTZ-Ph-AQ and PTZ-PhMe-AQ). The prompt fluorescence lifetime in cyclohexane is exceptionally long (τPF = 62.0 ns, population ratio: 99.2%) and 245.0 ns (93.5%) for PTZ-Ph-AQ and PTZ-PhMe-AQ, respectively (normally τPF <20 ns); the delayed fluorescence lifetimes for these two dyads were determined as τDF = 2.4 μs (6.5%) and 7.6 μs (0.8%), respectively. For the dyad containing a biphenylene linker (PTZ-Ph2Me-AQ), no TADF was observed. Charge-separated (CS) states were observed for PTZ-Ph-AQ and PTZ-PhMe-AQ, and the lifetimes were determined as 7.0 and 1.3 μs, respectively, indicating the triplet spin multiplicity of the CS state. The 3CS state lifetimes are shortened to 100 ns and 440 ns for the two dyads, respectively, in the polar solvent acetonitrile. For dyads with a longer linker, i.e., PTZ-Ph2Me-AQ, the CS state lifetime is not sensitive to solvent polarity (τCS = 1.8 and 1.3 μs in cyclohexane and acetonitrile, respectively). In reference dyads, where the PTZ unit is oxidized to sulfoxide, no CT absorption band and TADF were observed, which is attributed to the increased CS state energy (>3 eV) becoming higher than that of the AQ triplet (3AQ*) state (ca. 2.7 eV). These experimental evidence show that the presence of 1CS, 3CS, and 3LE (LE: locally excited) states sharing similar energy is essential for the occurrence of TADF. Population of the long-lived 3CS state (with a lifetime of a few μs) does not produce by itself TADF, because the ISC process of 1CS→3CS is nonsufficient. Femtosecond transient absorption spectra show that charge separation (CS) occurs readily (<5 ps) for most dyads, even in nonpolar solvents. Nanosecond pulsed laser-excited time-resolved electron paramagnetic resonance (TREPR) spectra show that either a spin correlated radical pair (SCRP) is formed, with the electron exchange energy 2J = +2.14 mT, or radical pairs with stronger interaction, |2J| > 6.57 mT. These studies are useful for in-depth understanding of the CS and ISC in compact electron donor-acceptor dyads and for design of efficient TADF emitters.

Ultrafast Photoinduced Dynamics of Quaterthiophene-Squaraine Hybrid Aggregates

Photoinduced energy transfer, charge transfer, and generation of sufficiently long-lived charge-separated (CS) states in the aggregated oligothiophenes are always challenging. Herein, we have coupled quaterthiophene (QTH) with a squaraine (SQR) dye in hybrid aggregates. A detailed time-resolved investigation using transient absorption spectroscopy and global target analyses revealed ultrafast photoinduced energy and electron transfer from QTH aggregates to SQR aggregates and the formation of a long-lived CS state in these hybrids. The pulse width limited energy transfer (<120 fs) occurred from the S1(Agg.)Ex. state, and the electron transfer occurred from both the S1(Agg.)Ex. state and the S1(Agg.)Rlx. state of QTH aggregates to the SQR aggregates at the timescales 131.5 ps and 3.3 ns, respectively. The resulting CS state lived for more than 8 ns. Moreover, the electrons of the QTH aggregates were prohibited to relax via the dark state and were extracted to the SQR aggregates which would lead to their successful utilization toward light-harvesting applications.

InP quantum dots: Stoichiometry regulates carrier dynamics.

The optical properties of non-toxic indium phosphide (InP) quantum dots (QDs) are impinged by the existence of characteristic deep trap states. Several surface engineering strategies have been adopted to improve their optical quality, which has promoted the use of InP QDs for various technological applications. An antithetical approach involves the effective utilization of the deep trap states in InP QDs to modulate back electron transfer rates. Here, we explore the influence of the core-size of InP on their In-to-P stoichiometry and charge transfer dynamics when bound to an acceptor molecule, decyl viologen (DV2+). The mechanism of interaction of InP and DV2+ based on the quenching sphere model established the presence of (i) a 1:1 complex of DV2+ bound on InP and (ii) immobile quenchers in the quenching sphere, depending on the concentration of DV2+. While the forward electron transfer rates from photoexcited InP to bound DV2+ does not substantially vary with an increase in core size, the back electron transfer rates are found to be retarded. Findings from inductively coupled plasma-optical emission spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS) reveal that the In to P ratio is higher for QDs with larger core size, which further brings about increased carrier trapping and a decreased rate of charge recombination. Furthermore, long-lived charge-separated states in DV2+ bound to InP, extending to hundreds of milliseconds, are obtained by varying the number of DV2+ in the quenching sphere of the QDs.

Confinement of Pyridine Derivatives into a Metal-Organic Framework Host as Electron Acceptors to Achieve Photoinduced Electron-Transfer.

The photoinduced electron-transfer (ET) process plays an irreplaceable role in chemical and biological fields exemplified by enzymatic catalysis, artificial photosystems, solar energy conversion, and so forth. Searching for a new photoinduced ET system is of great importance for the development of functional materials. Herein, a series of host-guest compounds based on a magnesium metal-organic framework (Mg-MOF) as a host and pyridine derivatives as guests have been presented. Notably, strong O-H···N hydrogen bond between the oxygen atom of μ2-H2O and the nitrogen atom of pyridine enables proton delocalization between water molecule and pyridine guest. Despite the absence of photochromic modules in these host-guest compounds, long-lived charge-separated states with distinct color changes can be formed after UV-light irradiation. The substituents in pyridines and the proton delocalization ability between the host and guests have a great influence on their photoinduced ET process to endow the MOF materials with tunable photoinduced charge-separated states.

The Green Box: Selenoviologen-Based Tetracationic Cyclophane for Electrochromism, Host–Guest Interactions, and Visible-Light Photocatalysis

The novel selenoviologen-based tetracationic cyclophanes (green boxes 3 and 5) with rigid electron-deficient cavities are synthesized via SN2 reactions in two steps. The green boxes exhibit good redox properties, narrow energy gaps, and strong absorption in the visible range (370-470 nm), especially for the green box 5 containing two selenoviologen (SeV2+) units. Meanwhile, the femtosecond transient absorption (fs-TA) reveals that the green boxes have a stabilized dicationic biradical, high efficiency of intramolecular charge transfer (ICT), and long-lived charge separation state due to the formation of cyclophane structure. Based on the excellent photophysical and redox properties, the green boxes are applied to electrochromic devices (ECDs) and visible-light-driven hydrogen production with a high H2 generation rate (34 μmol/h), turnover number (203), and apparent quantum yield (5.33 × 10-2). In addition, the host-guest recognitions are demonstrated between the green boxes and electron-rich guests (e.g., G1:1-naphthol and G2:platinum(II)-tethered naphthalene) in MeCN through C-H···π and π···π interactions. As a one-component system, the host-guest complexes of green box⊃G2 are successfully applied to visible-light photocatalytic hydrogen production due to the intramolecular electron transfer (IET) between platinum(II) of G2 and SeV2+ of the green box, which provides a simplified system for solar energy conversion.

In situ constructing atomic interface in ruthenium-based amorphous hybrid-structure towards solar hydrogen evolution

The rational steering and construction of efficient and stable atomic interfaces is highly desirable but rather challenging in solar energy conversion. Here, we report an in-situ oxygen impregnation strategy to build abundant atomic interfaces composed of homogeneous Ru and RuOx amorphous hybrid-mixture with ultrafast charge transfer, for solar hydrogen evolution with sacrificial agent free. Via in-situ synchrotron X-ray absorption and photoelectron spectroscopies, we can precisely track and identify the gradual formation of atomic interfaces towards homogeneous Ru-RuOx hybrid-structure at the atomic level. Benefiting from the abundant interfaces, the amorphous RuOx sites can intrinsically trap the photoexcited hole within an ultrafast process (<100 fs), and the amorphous Ru sites enable subsequent electron transfer (~1.73 ps). Hence, this hybrid-structure triggers long-lived charge-separated states, and results in a high hydrogen evolution rate of 60.8 μmol·h−1. This design integrating the two sites fulfilled each half-reaction in a single hybrid-structure suggests potential guidelines towards efficient artificial photosynthesis.

A Symmetry-Broken Charge-Separated State in the Marcus Inverted Region.

We report a long-lived charge-separated state in a chromophoric pair (DC-PDI2 ) that uniquely integrates the advantages of fundamental processes of photosynthetic reaction centers: i) Symmetry-breaking charge-separation (SB-CS) and ii) Marcus-inverted-region dependence. The near-orthogonal bichromophoric DC-PDI2 manifests an ultrafast evolution of the SB-CS state with a time constant of =0.35±0.02 ps and a slow charge recombination (CR) kinetics with =4.09±0.01 ns in ACN. The rate constant of CR of DC-PDI2 is 11 686 times slower than SB-CS in ACN, as the CR of the PDI radical ion-pair occurs in the deep inverted region of the Marcus parabola ( >λ). In contrast, an analogous benzyloxy (BnO)-substituted DC-BPDI2 showcases a ≈10-fold accelerated CR kinetics with lowering to ≈1536 in ACN, by virtue of a decreased CR driving force. The present investigation demonstrates a control of molecular engineering to tune the energetics and kinetics of the SB-CS material, which is essential for next-generation optoelectronic devices.

Thousand-Fold Enhancement of Charge-Separated State Lifetimes Caused by an Adamantane Bridge in Dimethylaniline-Anthracene and Dimethylaniline-Pyrene Dyads.

A long-standing challenge in photoinduced electron transfer research is the design of compact donor-acceptor dyads that can generate long-lived charge-separated (CS) states for use as sensitizers in solar energy harvesting. Reports of dyads exhibiting CS state lifetimes in the microsecond time domain are very rare. Herein, we report two compact donor-bridge-acceptor dyads exhibiting lifetimes in the microsecond domain. We employed an adamantane moiety as a bridge, and the lifetimes obtained are nearly 1000-fold larger when compared to those of the same donor-acceptor dyads bridged through C3-alkyl chains. In addition to long-lived CS state decays, slow formation of acceptor triplets was also observed via nanosecond flash photolysis. The long lifetime of the CS state is attributed to the extremely small value of the electronic coupling matrix element for the charge recombination compared to charge separation.

The effect of thionation of the carbonyl group on the photophysics of compact spiro rhodamine-naphthalimide electron donor-acceptor dyads: intersystem crossing, charge separation, and electron spin dynamics.

Herein, a spiro rhodamine (Rho)-thionated naphthalimide (NIS) electron donor-acceptor orthogonal dyad (Rho-NIS) was prepared to study the formation of a long-lived charge separation (CS) state via the electron spin control approach. The transient absorption (TA) spectra of Rho-NIS indicated that the intersystem crossing (ISC) occurs within 7-42 ps to produce the 3NIS state via the spin orbit coupling ISC (SOC-ISC). The energy order of 3CS (2.01 eV in n-hexane, HEX) and 3LE states (1.68 eV in HEX) depended on the solvent polarity. The 3NIS state having n-π* character and a lifetime of 0.38 μs was observed for Rho-NIS in toluene (TOL). Alternatively, in acetonitrile (ACN), the long-lived 3CS state (0.21 μs) with a high CS state quantum yield (ΦCS, 97%) was produced with the 3NIS state as the precursor and the CS took 134 ps. On the contrary, in the case of the reference Rho-naphthalimide (NI) Rho-NI dyad without thionation of its carbonyl group, a long-lived CS state (0.94 μs) with a high energy level (ECS = 2.12 eV) was generated even in HEX with a lower ΦCS (49%). In the presence of an acid, the Rho unit in the Rho-NIS adopted an open form (Rho-o) and the 3NIS state was produced within 24-47 ps with the 1Rho-o state as the precursor. Subsequently, slow intramolecular triplet-triplet energy transfer (TTET, 0.11-0.60 μs) produced the 3Rho-o state (9.4-13.6 μs). According to the time-resolved electron paramagnetic resonance (TREPR) spectra of NIS-NH2, the zero-field splitting (ZFS) parameter |D| and E of the triplet state were determined to be 6165 MHz and -1233 MHz, respectively, indicating that its triplet state has significant nπ* character, which was supported by its short triplet state lifetime (6.1 μs).

Harnessing Intermolecular Interactions to Promote Long-Lived Photoinduced Charge Separation from Copper Phenanthroline Chromophores

Facilitating photoinduced electron transfer (PET) while minimizing rapid charge-recombination processes to produce a long-lived charge-separated (CS) state represents a primary challenge associated with achieving efficient solar fuel production. Natural photosynthetic systems employ intermolecular interactions to arrange the electron-transfer relay in reaction centers and promote a directional flow of electrons. This work explores a similar tactic through the synthesis and ground- and excited-state characterization of two Cu(I)bis(phenanthroline) chromophores with homoleptic and heteroleptic coordination geometries and which are functionalized with negatively charged sulfonate groups. The addition of sulfonate groups enables solubility in pure water, and it also induces assembly with the dicationic electron acceptor methyl viologen (MV2+) via bimolecular, dynamic electrostatic interactions. The effect of the sulfonate groups on the ground- and excited-state properties was evaluated by comparison with the unsulfonated analogues in 1:1 acetonitrile/water. The excited-state lifetimes for all sulfonated complexes are similar to what we expect from previous literature, with the exception of the sulfonated heteroleptic complex whose metal-to-ligand charge-transfer (MLCT) lifetime in water has two components that are fit to 10 and 77 ns. For the sulfonated complexes, we detected reduced MV+• in both solvent environments following MLCT excitation, but control measurements in 1:1 acetonitrile/water with the unsulfonated analogues showed no PET to MV2+, indicating that electrostatically driven supramolecular assemblies of the sulfonated complexes with MV2+ facilitate the observed PET. Additionally, the strength of the intermolecular interactions driving the formation of these assemblies changes drastically with the solvent environment. In 1:1 acetonitrile/water, PET occurred from both sulfonated complexes with quantum yields (ΦET) of 2-3% but increased to a remarkable 98% for the sulfonated heteroleptic complex with a 3 μs CS-state lifetime in water.

Low-Toxicity ZnSe/ZnS Quantum Dots as Potent Photoreductants and Triplet Sensitizers for Organic Transformations.

Colloidal quantum dots (QDs) can photocatalyze diverse organic reactions. However, reported QD-photocatalysts often contain highly-toxic elements Cd or Pb, and have not surpassed prototypical transition-metal complexes in terms of their photoredox power or excited-state energy. Here we report low-toxicity ZnSe/ZnS core/shell QDs as potent visible photocatalysts to drive challenging organic transformations. To overcome the limitation of short excited-state lifetime of the QDs, we functionalize their surfaces with benzophenone ligands which can rapidly extract electrons from photoexcited QDs and sustain long-lived charge-separated states. The benzophenone anions function as potent electron relay to drive dehalogenation of aryl chlorides and additive-free polymerization of acrylates. Alternatively, the QDs are functionalized with biphenyl ligands to store energy in long-lived, energetic triplets, enabling [2+2] homo-cycloaddition of styrene and cycloaddition of carbonyls with alkenes.

Studies on crystal structures, optical, dyeing and biological properties of protoberberine alkaloids and their supramolecular salts

The novel Palmatine (PLT)-based supramolecular salt palmatine-sulfosalicylic acid (PLT-SSA) was designed and synthesized, and its structures was determined by the single crystal X-ray diffraction. It is found that PLT-SSA exhibited enhancing thermodynamic stability, fluorescence intensity and emission lifetime in crystal state, which indicated that these structures and aromatic rings may give more overlap between the host–guest units and give rise to a long-lived charge-separated state. In addition, the dyeing properties and toxicity of these protoberberine alkaloid (BBC and PLTCl) and their supramolecular salts will be developed in this work used as yellow dyes for development multifunctional fabrics.

Enhanced photocatalytic H2 evolution based on a polymer/TiO2 film heterojunction

Polymer heterojunctions have emerged as promising photocatalysts for the photocatalytic hydrogen evolution. However, they are usually used in the form of suspended powder due to the low solubility and lack of anchoring groups to hybridize with inorganic semiconductor oxides. Yet polymer film heterojunctions with convenient separation and recycling potential are more suitable for large-scale water splitting. Herein, a new solution-processable polymer PDBCOOH with biphenyl as the electron donor and diketopyrrolopyrrole (DPP) containing carboxyl group as the electron acceptor has been designed and synthesized. Surface anchoring of PDBCOOH to TiO2 films through covalent bonding formed polymer-TiO2 film heterojunctions that achieved a recorded photocatalytic H2 production rate of 11.9 mmol/m2/h without Pt co-catalyst and was 88.8 times higher than that of pristine TiO2 film. Transient absorption spectroscopy confirms ultrafast polymer excited state electron injection into TiO2, long-lived charge separated state, and unity yield of polymer hole regeneration. Photoelectrochemical experiments combined with density functional theory calculation further demonstrate that polymer PDBCOOH/TiO2 film heterojunctions not only accelerate the charge transfer but also significantly improve the hydrogen evolution rate and stability of the photocatalysts. This work offers a new strategy for obtaining stable and efficient photocatalysts by using the covalent anchoring strategy of polymer/TiO2 film heterojunction.

How does the metal doping in mixed metal MOFs influence their photodynamics? A direct evidence for improved photocatalysts

Mixed-metal organic frameworks (MMOFs) have arisen as one of the most promising photocatalysts for a wide number of reactions. In general, the introduction of a second or even a third metal atom in the MOFs metal cluster, having a better overlap with the π∗ orbital of the organic linker, enhances the photocatalytic activity of the MOFs. This can be a consequence of a more favorable ligand-to-cluster charge transfer (LCCT) process in the MMOFs, which in fact generates a higher population of long-lived charge-separated states (CSSs), the latter being the driving force of a photocatalytic reaction. However, proving a direct relation between these photo processes and the improved photocatalytic performance in MMOFs frequently remains elusive. Hence, herein we perform an exhaustive and systematic spectroscopic and photodynamical characterization of three UiO-66-NH2-type MOFs, where the metal cluster composition is varied from 100% Zr, a mixture of Zr/Ce (80/20%), and a mixture of Zr/Ce/Ti (70/7/23%). In comparison with the linker photodynamics, we observe the opening of new deactivation channels in the MOFs, associated with the LCCT phenomenon with time constants of 5–7 ps and 70–90 ps. Upon the successive incorporation of Ce and Ce/Ti in the MOFs, the LCCT becomes more efficient, which is reflected in the quenching of the photoluminescence quantum yield and in the generation of a higher population of CSSs, demonstrated by the flash photolysis experiments. These observations are in agreement with the photodegradation of a pollutant dye, Nile Blue, where the trimetallic MOF shows higher activity than the monometallic one. Hence, our results provide conclusive experimental evidence for the relationship between the photodynamics of the MMOFs and their photocatalytic activities.

Selenoviologen-Appendant Metallacycles with Highly Stable Radical Cations and Long-Lived Charge Separation States for Electrochromism and Photocatalysis.

Two coordinated metallacycles (rhomboid for M1, hexagonal for M2) with selenoviologens (SeV2+ ) pendants were synthesized via coordination-driven hierarchical self-assembly. M1/M2 with rigid and discrete metallacyclic cores showed tunable optoelectronic properties due to strong π-π stacking and push-pull electron structures. Femtosecond transient absorption (fs-TA) revealed that the formation of macrocyclic structure can not only enhance the stability of radical cation, but also improve the efficiency of intramolecular charge transfer and produce a long-lived charge separation state. The electrochromic performances of M1/M2-based devices were exhibited to show decent radical stabilization. By using M1/M2 as the photocatalyst, the improved catalytic efficiency (>80 %) of visible-light-induced cross-dehydrogenative coupling (CDC) reactions was achieved due to the highly stable radical cations and long-lived charge separation states, which were also confirmed by fs-TA.

(Invited) Ultrafast Formation of Long-Lived Charge-Separated State at High Energy Level By Two-Photon Ionization

Photoinduced electron transfer reactions play an important role in various photo-energy conversion processes. A key transient species enabling these processes is the charge-separated (CS) state produced by electron transfer, and its large formation rate constant, high energy level and long lifetime are required for its efficient utilization to the subsequent energy conversion and photoredox reactions. However, the formation rate constant is mutually correlated with the energy gap of electron transfer reactions, and it is difficult to optimize these parameters simultaneously, as shown by the Marcus theory and experimental investigations accumulated to date. In the present study, to create the CS state with the large formation rate, high energy level and long lifetime, we experimentally demonstrated an electron transfer reaction driven by two-photon ionization using a model system of pyrene (Py) as an electron donor and biphenyl (BP) as an acceptor. Photoionization enables ultrafast electron ejection from the donor to the acceptor which is 3-4 nm away from the donor. This long interionic distance effectively inhibits the geminate recombination, and the high energy level of the produced CS state is realized thanks to total energy of two photonsWe first investigated two-photon ionization of pyrene in the absence of the electron acceptor. Photoinduced dynamics of pyrene in acetonitrile solution was investigated under various excitation intensities using transient absorption spectroscopy. Upon photoexcitation at 355 nm, the absorption band at 445 nm, which is ascribable to the radical cation of pyrene, was observed with the S1 state absorption under higher excitation power, while only the S1 absorption appears at low intensities. This result shows that pyrene is ionized by the multiphoton process. Furthermore, the excitation power dependence of this ionization was simulated by a numerical simulation to quantitatively analyze the ionization quantum yield in higher excited state. The absorption signal intensities of the S1 state and radical cation were reproduced by the simulation, and the ionization yield was estimated to be 0.20.The excitation wavelength effect on the ionization was also investigated for optimization of the condition to produce the radical cation. The ionization dynamics was systematically measured by photoexcitation at 340, 355 and 370 nm. The absorption peak due to the radical cation is scarcely seen under 340 nm excitation condition. Under the 370 nm excitation, on the other hand, the quantity of the produced radical cation was maximized among the three conditions. This difference can be interpreted by distinct resonance of the excitation wavelength with the S1-S0 absorption. That is, under 370 and 355 nm excitation where the molar absorption coefficients were respectively 180 and 340 M-1cm-1, the S1 state produced by the first photon absorption can further absorbs the second photon in the excitation pulse. However, under 340 nm excitation at which the absorption coefficient is 4600 M-1cm-1, the second photon absorption by the S1 state is inhibited by the large absorption of the major remaining ground state molecules, which behaves as an intrinsic filter to hide the Sn-S1 absorption. Thus, the stepwise two-photon excitation does not effectively proceed under this condition. Taken together, the photoexcitation at the wavelength region, where the ground state absorption is not prominent, is crucial for efficient ionization driven by stepwise two-photon excitation.We finally performed the proof-of-concept experiments on two-photon ionization-driven electron transfer of the pyrene-biphenyl system. Under the intense excitation condition optimized above, pyrene was excited in a two-photon manner, which can be confirmed by the instantaneous appearance of the radical cation. Other absorption bands show up around 400 and 640 nm in a few tens of picoseconds. These bands are attributable to the radical anion of biphenyl. A detailed global analysis revealed that the anion radical is produced with a time constant of 200 fs, which is followed by vibrational cooling of the resultant ion radicals and the S1 state with a time constant of 16 ps. This observation demonstrates that an electron ejected from pyrene is directly captured by biphenyl on an ultrafast timescale. The energy level of the CS state thus formed was estimated to be higher than that of the S1 state of pyrene by 0.53 eV, which is also confirmed by non-quenching behavior of pyrene fluorescence by biphenyl. In addition, the subsequent ionic dissociation without a remarkable geminate recombination in the sub-nanosecond to nanosecond time region effectively avoids the quantity loss of the CS state. The results in the present work show that two-photon excitation method enables ultrafast formation of the long-lived CS state at a high energy beyond the traditional framework of electron transfer reactions. Figure 1

(Invited) Untethering the Tether Towards Spontaneously Self-Assembled Donuts

Functional materials comprised of spontaneously self-assembled electron donor and acceptor entities capable of generating long-lived charge-separated states upon photo-illumination are in great demand as they are key in building the next generation of light energy harvesting devices. However, creating such well-defined architectures is challenging due to the intricate molecular design, multi-step synthesis, and issues associated in demonstrating long-lived electron transfer.Here, we have newly synthesized, by tether-directed functionalization, a [60]fullerene e-bisadduct carrying two Zn-porphyrins (Figure), and demonstrate supramolecular organization and photophysical events. Remarkably, the supramolecular assembly of the present bisporphyrin-C60 forms donut-shape aggregates, primarily via π-π type charge transfer interactions. Upon photoexcitation, the supramolecular assembly generates long-lived charge-separated states of »1−40 μs lifetime due to electron/hole delocalization within the supramolecular structureReference Caballero, M. Barrejón, J. Cerdá, J. Aragó, S. Seetharaman, P. de la Cruz, E. Ortí, F. D’Souza, F. Langa. J. Am. Chem. Soc. 2021, 143, 11199. Figure 1

Long-Lived Internal Charge-Separated State in Two-Dimensional Metal–Organic Frameworks Improving Photocatalytic Performance

Long-Lived Internal Charge-Separated State in Two-Dimensional Metal–Organic Frameworks Improving Photocatalytic Performance

Enhancing photocurrent of dye-sensitized solar cells through solvent modulating aggregation of dyes

Aggregation of organic molecules plays a key role in determining the photoelectronic properties of various devices. However, the formation of aggregates is an outcome of complex synergistic effects of various intermolecular forces, and changes with the molecular structure and environment. Here we exploit the aggregation of two dyes with (MTPABT-Pyc) or without (MTPAcc) the nanosecond long-lived charge separation state and their effect on photovoltaic performance of dye-sensitized solar cells (DSSCs). Different solvent systems were selected to modulate the interactions between solvents and dye molecules for the effects on photophysical processes. Combining the experimental results on the solvent effect on dye aggregation with theoretical calculations reveals that MTPAcc inclines to form H-aggregation on the TiO2 surface because of the decisive role of its molecular structure. The solvent regulation has a great impact on MTPABT-Pyc which can make aggregates transform between H-aggregation and J-aggregation. The effects of aggregation on the device performance of two dyes are completely opposite. High performance of MTPAcc depends on the co-adsorbent chenodeoxycholic acid, which could suppress the dye aggregation. In contrast, the aggregation of MTPABT-Pyc will not harm the charge separation and transportation processes in devices and shows a positive effect on the cell performance due to the aggregation exhibiting broader absorption bands. As the photocurrent contribution by the aggregation-induced long-wavelength absorption increases from 9% (H-aggregation) to 34% (J-aggregation), the short-circuit current (Jsc) and the power conversion efficiency (PCE) of MTPABT-Pyc increased by 13% and 14%, respectively. These results pave a new way for taking full advantage of the aggregation of molecules to realize high-performance light-to-current conversion.

Two halogen and hydrogen-bonding modulated photochromic Cd(Ⅱ) complexes with long-lived charge-separated state and acetonitrile erasable behavior

Two isostructural cadmium complexes [Cd4(2-abpt)2(H2O)2X8]·2H2O (X = Cl (1), Br (2)) based on multidentate chelating ligand 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole (2-abpt) with discrete tetranuclear structures have been synthesized and display halogen-modulated photochromic behaviors and switchable photoluminescence. Importantly, their colored photoproducts possess hydrogen-bonding interactions induced ultralong-lived charge-separated state and acetonitrile erasable behavior.