Photoinduced Electron Transfer Systems Research Articles

Custom-printed microfluidic chips using simultaneous ratiometric fluorescence with "Green" carbon dots for detection of multiple antibiotic residues in pork and water samples.

In the evolving field of food safety, rapid and precise detection of antibiotic residues is crucial. This study aimed to tackle this challenge by integrating advanced inkjet printing technology with sophisticated microfluidic paper-based analytical devices (µPADs). The µPAD design utilized "green" quantum dots synthesized via an eco-friendly hydrothermal method using green white mulberry leaves as the carbon source, serving as the key fluorescent detection material. The action mechanism involved a photoinduced electron transfer system using red carbon dots (CDs) as electron donors and blue CDs combined with two-dimensional layered molybdenum disulfide (MoS2) nanosheets as electron acceptors. This system could quickly detect antibiotics within 10min in pork and water samples, demonstrating high sensitivity and recovery rates: 6.5pmol/L at 99.75%-110% for sulfadimethoxine, 3.3pmol/L at 99%-105% for sulfamethoxazole, and 8.5pmol/L at 98.5%-105% for tetracycline. It achieved a relative standard deviation under 5%, ensuring reliability and reproducibility. The fabricated sensor offered a promising application for the rapid and efficient on-site detection of antibiotic residues in food.

Controlled photoinduced electron transfer via triplet in polymer matrix using electrostatic interactions

Drawing inspiration from highly efficient natural photosynthetic systems, we developed an artificial photoinduced electron transfer (PET) system within a poly(N-methyl-4-vinylpyridinium) (P4VPMe) polymer matrix. This system features 5,10,15,20-tetrakis-(4-sulfonatophenyl) porphyrin (TPPS) and its zinc complex (ZnTPPS) as electron donors and methylviologen (MV2+) as the electron acceptor. In the presence of an excess of P4VPMe, ZnTPPS exists as individual molecules rather than self-aggregating, favoring PET. Under these conditions, P4VPMe inhibits the formation of ground-state charge-transfer complex between ZnTPPS and MV2+. This shifts the main PET process from singlet to triplet states. ZnTPPS in an excess of P4VPMe demonstrates over a tenfold increase in catalytic activity for the photoinduced oxidation of MV2+ compared to ZnTPPS alone.

(Invited) Corannulene-Based Molecular Nanographenes: Synthesis, Reduction, Supramolecular Complexation and Photophysical Properties

The outstanding electronic properties of graphene-based materials make them one of the most promising assets for application in the electronics industry of the XXI century. Encouraged by these properties, a great number of materials scientists are currently engaged in the development of the emergent field of 2D materials. In the last decade, the reduction of the dimensionality to 1D (nanoribbons) and 0D (nanographenes NGs, or graphene quantum dots, GQDs) have become an important research topic by their singular properties. In this regard, the quantum confinement of the electrons and the edge effects of these graphene derived structures makes possible the bandgap opening and, therefore, the appearance of a semiconductor behavior.The bottom-up preparation of these new structures, specifically employing stepwise organic synthesis, lead to monodisperse molecular nanographenes with atomically controlled morphology and, therefore, to the control of photophysical properties at will. An example of this synthetic management is the insertion of non-hexagonal rings in the honeycomb pattern of NGs, endowing Gaussian curvature to these structures and making molecules with bowl or saddle shapes.Our research group has described the wet synthesis of curved corannulene-based nanographenes by a stepwise Sonogashira–[4+2]–Scholl strategy.[1] Using bromocorannulene 1 as starting material, and depending on the temperature and the oxidant agent used in the Scholl reaction, a [6]helicene corannulene-based nanographene 2 or a positively-negatively curved nanographene 3 were prepared. These molecular curved NGs present interesting photophysical properties such as thermal activated delayed fluorescence (TADF) or dual emission.[2] Additionally, the multi-electron acceptor nature of molecular NGs allows the reduction with alkali metals that normally remains hosted in the pockets of curved nanographenes leading to potential energy storage systems. Within a collaborative work, the reduction of nanographene 2 with Na metal has recently been performed.[3] The formation of a “naked” dianion C76H64 2– (2 2–) solvent separated from the two cationic moieties was observed affording unprecedented selectively reduced species. DFT calculations revealed significant changes in the electron density and the inversion of the ring current aromaticity.Finally, concave–convex interactions between curved nanographenes and fullerenes are known to lead to supramolecular complexes with special interest as photoinduced electron transfer systems, mimicking the photosynthetic process. In a collaborative work,[4] the supramolecular complexation of nanographene 3 with C60 was experimentally monitored by H NMR spectroscopy and studied by DFT calculations.The formation of complexes with stoichiometries 2:1, 1:1 and 1:2 is possible. Furthermore, when the complex was irradiated at 460nm, the formation of the C60 radical anion is observed in an amazing photoinduced electron transfer process. References 1 J. M Fernández-García, P. Evans, S. Medina Ribero, I. Fernández, D. García-Fresnadillo, J. Perles, J. Casado, N. Martín, J. Am. Chem. Soc. 2018, 140, 17188.2 Manuscript in preparation.3 Z. Zhou, Y, Zhu, J. M. Fernández-García, Z. Wei, I. Fernández, M. Petrukhina, N. Martín et al., Chem. Commun. 2022, 58, 5574.4 S. Zank, J. M. Fernández-García, A. J. Stasyuk, A. A. Voityuk, M. Krug, M. Solà, D. Guldi and N. Martín, Angew. Chem. Int. Ed. 2022, 61, e202112834 Figure 1

(Invited) Synthesis and Photophysical Properties of Cyclometalated Iridium(III) Complexes Having Arylborane Units Toward the Photoreaction

Cyclometalated iridium(III) complexes are known to show intense absorption and bright phosphorescence at room temperature and have been applied to photosensitizer and light-emitting materials. For such applications of the complexes, the study of synthetic tuning of the HOMO/LUMO energies of the complexes through introduction of electron-withdrawing substituent(s) on the ligand and/or that of heteroaromatic ring(s). By introducing another interaction site into Ir complexes, it is considered that a more sensitive HOMO/LUMO energies change occurs. Therefore, we focused on the arylborane compounds. When boron has a tri-substituted structure, it has an vacant p-orbital and has a planar structure. Since this vacant p-orbital shows Lewis acidity, it is considered that it acts as an acceptor site. Furthermore, the excited-states of arylborane derivatives are expected to be utilized to photoinduced electron transfer systems. Therefore, in this study, we synthesized a novel iridium(III) complexes having various boron substituents, which is thought to cause intramolecular charge transfer, and investigated its spectroscopic properties. Figure 1

Modulating Photoinduced Electron Transfer between Photosensitive MOF and Co(II) Proton Reduction Sites forBoosting Photocatalytic Hydrogen Production.

Photocatalytic hydrogen production viawater splitting is the subject of intense research. Photoinduced electron transfer (PET) between a photosensitizer (PS) and a proton reduction catalyst is a prerequisite step and crucial to affecting hydrogen production efficiency. Herein, three photoactive metal-organic framework (MOF) systems having two different PET processes where PS and Co(II) centers are either covalently bonded or coexisting to drive photocatalytic H2 production arebuilt. Compared to these two intramolecular PET systems including CoII -Zn-PDTP prepared from the post-synthetic metalation toward uncoordinated pyridine N sites of Zn-PDTP and sole cobalt-based MOF Co-PDTP, the CoII (bpy)3 @Zn-PDTP system impregnated by molecular cocatalyst possessing intermolecular PET process achieves the highest H2 evolution rate of 116.8mmol g-1 h-1 over a period of 10h, about 7.5 and 9.3 times compared to CoII -Zn-PDTP and Co-PDTP in visible-light-driven H2 evolution, respectively. Further studies reveal that the enhanced photoactivity in CoII (bpy)3 @Zn-PDTP canbe ascribed to the high charge-separation efficiency of Zn-PDTP and the synergistic intermolecular interaction between Zn-PDTP and cobalt complexes. The present work demonstrates that the rational design of PET process between MOFs and catalytic metal sites can be a viable strategy for the development of highly efficient photocatalysts with enhanced photocatalytic activities.

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.

Photosensitized Radical-Anion-Driven Metal-Free Selective Reduction of Aldehydes Using Graphene Oxide as an Electron Relay Mediator under Visible Light.

Despite the modern boost, developing a new photocatalytic system for the reduction of aldehydes is still challenging due to their high negative reduction potential. Herein, we have used a metal-free photoinduced electron-transfer system based on a cheap and readily available organic dye eosin Y (EY), graphene oxide (GO), and ammonium oxalate (AO) for photocatalytic reduction of structurally diverse aldehydes under sustainable conditions. The protocol shows remarkable selectivity for the photocatalytic reduction of aldehydes over ketones. The decisive interaction of GO and AO with the various states of EY (ground, singlet, triplet, and radical anions), which are responsible for the commencement of the reaction, was examined by various theoretical, optical, electrochemical, and photo-electrochemical studies. The synergetic system of GO, EY, and AO is appropriate for enhancing the separation efficiency of visible-light-induced charge carriers. GO nanosheets act as an electron reservoir to accept and transport photogenerated electrons from the photocatalytic system to the reactant. The reduction of the GO during the process ruled out the back transfer of photoexcited charges. Control experiments explained that the reaction involves two stages: electron transfer and protonation. This process eliminates the necessity of precious-metal-based photocatalysts or detrimental sacrificial agents and overcomes the redox potential limitations for the photoreduction of aldehydes.

Room temperature photochromism and photoinduced slow magnetic relaxation of cyanometallic supramolecular hybrid salts

A supramolecular photoinduced electron transfer system is constructed from terpyridinium hexacyanometalate(iii) hybrid salts along with an unprecedented room-temperature light-induced off→on magnetizing and slow magnetization relaxation behaviour.

Ultrafast Electron Transfer in a Self-Assembling Sulfonated Aluminum Corrole-Methylviologen Complex.

Photoinduced electron transfer systems can mimic certain features of natural photosynthetic reaction centers, which are crucial for solar energy production. Among other tetra-pyrroles, the versatile chemical and photophysical properties of corroles make them very promising donors applicable in donor-acceptor complexes. Here, we present a first comprehensive study of ultrafast photoinduced electron transfer in a self-assembling sulfonated aluminum corrole-methylviologen complex combining visible and mid-IR transient absorption spectroscopy. The noncovalent D-A association of the corrole-methylviologen complex has the great advantage that photoinduced charge separation becomes possible even though the back electron transfer (BET) rate is large. Initial forward electron transfer from corrole to methylviologen is observed on an ∼130 fs time scale. Subsequent back electron transfer takes place with τBET = (1.8 ± 0.5) ps, revealing very complex relaxation dynamics. Direct probing in the mid-IR allows us to unravel the back electron transfer and cooling dynamics/electronic reorganization. Upon tracing the dynamics of the methylviologen-radical marker band at 1640 cm-1 and the C═C stretching of corrole at around 1500 cm-1, we observe that large amounts of excess energy survive the back transfer, leading to the formation of hot ground state absorption. A closer examination of the signal after 300 ps, surviving the back transfer, exhibits a charge-separation yield of 10-15%.

The donor–acceptor dyad based on high substituted fullero[70]pyrrolidine-coordinated manganese (III) phthalocyanine for photoinduced electron transfer

Donor-acceptor dyads based on manganese porphyrins/phthalocyanines and fullerene derivatives with N-basicity centers have proved as promising photoinduced electron-transfer systems for photovoltaic devices, biologically active compounds, and molecular magnetic materials. The macroheterocyclic chromophore characterized by rich UV–visible-near IR absorption is the basis for the applications above. The problem of the synthesis and the characterization of new effective dyads was solved in this work on the example of the self-organizing system consisting of (octakis-3,5-di-tert-butylphenoxy)phthalocyaninato)manganese(III) acetate, (AcO)MnPc(3,5-di-tBuPhO)8, 2′,5-di(pyridin-2′-yl)-3,4-fullero[70]pyrrolidine, Py2C70, and toluene. The phthalocyanine-fullerene dyads in the molecular and cationic form (respectively (AcO)(Py2C70)MnPc(3,5-di-tBuPhO)8 and [(Py2C70)MnPc(3,5-di-tBuPhO)8]+(AcO)-) were observed and described using the chemical kinetics/thermodynamics, UV–vis, IR, 1H NMR spectroscopy and mass spectrometry methods. The 1: 1 stoichiometry of both dyads was confirmed; the equilibrium and rate constant value, K= (4.86 ± 0.56) × 104 L mol−1 and k = (4.455 ± 3.37) × 10-5 s−1 was observed for the formation of molecular and cationic dyad, respectively. The study of (AcO)MnPc(3,5-di-tBuPhO)8 and [(Py2C70)MnPc(3,5-di-tBuPhO)8]+AcO- femtosecond transient absorption spectra points to the photoinduced electron transfer in the dyad, for which the lifetimes and the rate constants of charge separation (τCS, kCS) and charge recombination (τCR, kCR) were defined. The analysis of the relationship of the dyad physicochemical parameters with the molecular structure is represented using previously published data.

Enzyme- and label-free fluorescence microRNA biosensor based on the distance-dependent photoinduced electron transfer of DNA/Cu nanoparticles

Herein, we report a convenient enzyme- and label-free fluorescent biosensor for the quantitative detection of microRNA (miRNA). It is the first time that the distance-dependent property of photoinduced electron transfer (PET) has been observed between G-quadruplex/hemin (G/hemin) complexes and fluorescent DNA/Cu nanoparticles (NPs), accompanied by the change of the fluorescence intensity from DNA/Cu NPs. This innovative PET system could achieve the sensitive and specific determination of nucleic acids such as DNA and RNA based on the design of versatile detection sequences. With the existence of the target miRNA, the original flexible single-strand DNA detection probe becomes rigid DNA/RNA heteroduplexes. Therefore the PET could be hindered because of the prolonged distance from the electron donor-Cu NPs to electron acceptor-G/hemin complexes. Hence, a fluorescence light-up miRNA biosensor was established via the monitoring of the fluorescence signal of the formed DNA/Cu NPs. Compared to other reported PET-based miRNA determination methods, the distance-dependent PET of Cu NPs-based biosensor only needs to adjust the detection probe sequences for various miRNAs assays. This strategy is effective for the determination of the miRNA let-7a over a linear range of 0.5 to 100 nM, with a relatively low limit of detection of 0.2 nM. Besides, this novel assay has been successfully employed for the enzyme- and label-free fluorescence detection of miRNA from real samples.

Functionalization of Bipyrenol: Potential Precursors for Advanced Chiral Molecules

Considering the widespread interest in the chiroptical properties of materials, especially circularly polarized luminescence (CPL), the functionalization of bipyrenol (BPy) was carried out aiming at future advanced chiral materials (ACMs) in which BPy shows a high quantum yield and clear CPL spectra. To create ACMs using BPy units that contain nucleophilic substituents, amine and thiol were selected as the functional group and attached to BPy by means of alkyl linkages. The obtained thiol and amine derivatives are stable under ambient conditions. To demonstrate the potential of these molecules, photoinduced electron-transfer systems were synthesized.

Metal-organic supramolecular nanoarchitectures by Ru(II) bis-(terpyridine)-bridged pillar[5]arene dimers with triphenylamine

A metal-organic photoinduced electron transfer (PET) supramolecular nanoarchitecture comprised of Ru(II) bis(terpyridine)-modified pillar[5]arene (electron acceptor) and triazole triphenylamine amyl cyanide (electron donor) has been designed and constructed. Through the comparison of diverse solvents and acceptors, the two conditions, i.e., modification of pillar[5]arene to donor and weak polar solvent are benefit for the occurrence of “efficient PET” because of shorter D-A distance in the presence of pillar[5]arene. Crucially, the fluorescence and PET process of the supramolecular assembly could be further modulated by solvent conversion and another competitive guest. The study provides a supramolecular method to design and construct tunable PET systems and PET-based smart materials.

Dopamine-functionalized upconversion nanoparticles as fluorescent sensors for organophosphorus pesticide analysis

Organophosphorus pesticide (OP) residues in agricultural products, herbal medicines and environment have attracted increasing concerns because they cause high healthy risk. Herein, a tyrosinase-mediated photoinduced electron transfer system was constructed for OPs analysis by using dopamine-functionalized upconversion nanoparticles (UCNPs) as fluorescent (FL) sensors. Dopamine quinone was produced by tyrosinase-mediated oxidation of dopamine on the surface of UCNPs, which acted as electron accepter to quench the FL emission of UCNPs. The FL quenching was inhibited by OP since it inhibited the activity of tyrosinase. Chlorpyrifos was used as a model analyte to investigate the feasibility of the FL sensor for the analysis of OPs. Under the optimal conditions, chlorpyrifos can be analysed in a wide range of 1.0 ‒ 1000 ng mL−1, with a detection limit of 0.38 ng mL−1 (3σ). Some other groups pesticides, including organonitrogen pesticide, organochlorine pesticide and chloronicotinyl insecticide all showed negligible interference. The proposed sensor was successfully used to analyse chlorpyrifos spiked in Balloonflower and Angelica with acceptable recovery values of 95.4–120.0%, demonstrating its application potential for real samples. It exhibits some advantages like low cost, high sensitivity and free of autofluorescent interference and photobleaching.

Photoinduced electron transfer from polymer-templated Ag nanoclusters to G-quadruplex-hemin complexes for the construction of versatile biosensors and logic gate applications.

In this paper, fluorescent Ag nanoclusters (Ag NCs) templated by hyperbranched polyethyleneimine (PEI) are utilized as a versatile probe through the photoinduced electron transfer (PET) between PEI-Ag NCs and G-quadruplex-hemin complexes. In the presence of hemin and target molecule, the specific conjugation with its aptamer induces the conformational change of the DNA sequence, releasing the G-quadruplex sequence part. Once the G-quadruplex-hemin complexes are introduced, electron transfer from the PEI-Ag NCs to G-quadruplex-hemin complexes occurs, resulting in fluorescence quenching. Through changing the sensing DNA sequence, this novel PET system enables the specific detection of target DNA and adenosine triphosphate (ATP) with the wide linear range of 1-200nM and 5-500nM, respectively, and the corresponding limit of detection as low as 0.3nM for target DNA and 1.5nM for ATP. In addition, the proposed method is successfully applied to the determination of ATP in human serum samples with satisfactory recoveries, and a logic gate is fabricated using target molecules and hemin as inputs and the fluorescence signal of PEI-Ag NCs as an output.

Light-induced hydrogen production by photosystem I–Pt nanoparticle conjugates immobilized in porous glass plate nanopores

In recent years, a number of light-induced hydrogen production systems composed of photosystem I (PSI) and hydrogen production catalysts (e.g. hydrogenases and Pt nanoparticles) have been reported. However, the utility of these systems under aerobic conditions is limited due to their poor stability in the presence of oxygen. The development of light-induced hydrogen production systems that work under aerobic conditions is, therefore, of great importance to establish artificial photosynthetic devices. Ideally, these systems should utilise water as an electron source, via water splitting by photosystem II (PSII). We report the construction of a novel light-induced hydrogen production system composed of PSI-platinum nanoparticle conjugates and cytochrome c 6 (cyt c 6) immobilised in nanoporous glass plates (PGP50, 50-nm pore diameter). PSI trimer (PSIt) from Thermosynechococcus elongatus and Pt nanoparticles (PtNPs) were conjugated via electrostatic interactions (PSIt-PtNP). PSIt-PtNP and cyt c 6 were spontaneously absorbed in nanopores of PGP50 without denaturation. Upon irradiation in the presence of ascorbate as a sacrificial electron donor, catalytic H2 evolution was observed for PSIt-PtNP immobilised in the pores of PGP50 (PSIt-PtNP/PGP50) under both anaerobic and aerobic conditions, indicating that an effective photoinduced electron transfer system had been established. PSIt-PtNP/PGP50 was found to exhibit improved oxygen resistivity over the homogeneous solution system consisting of PSIt-PtNP, cyt c 6, and ascorbate, suggesting that the PSIt-PtNP/PGP50 system could be a potential candidate for artificial photosynthetic systems. The distribution of the components, PSIt-PtNP and cyt c 6, in PGP50 was characterised to discuss the efficiency of light-induced hydrogen production.

In vivo retinal and choroidal hypoxia imaging using a novel activatable hypoxia-selective near-infrared fluorescent probe.

Retinal hypoxia plays a crucial role in ocular neovascular diseases, such as diabetic retinopathy, retinopathy of prematurity, and retinal vascular occlusion. Fluorescein angiography is useful for identifying the hypoxia extent by detecting non-perfusion areas or neovascularization, but its ability to detect early stages of hypoxia is limited. Recently, in vivo fluorescent probes for detecting hypoxia have been developed; however, these have not been extensively applied in ophthalmology. We evaluated whether a novel donor-excited photo-induced electron transfer (d-PeT) system based on an activatable hypoxia-selective near-infrared fluorescent (NIRF) probe (GPU-327) responds to both mild and severe hypoxia in various ocular ischemic diseases animal models. The ocular fundus examination offers unique opportunities for direct observation of the retina through the transparent cornea and lens. After injection of GPU-327 in various ocular hypoxic diseases of mouse and rabbit models, NIRF imaging in the ocular fundus can be performed noninvasively and easily by using commercially available fundus cameras. To investigate the safety of GPU-327, electroretinograms were also recorded after GPU-327 and PBS injection. Fluorescence of GPU-327 increased under mild hypoxic conditions in vitro. GPU-327 also yielded excellent signal-to-noise ratio without washing out in vivo experiments. By using near-infrared region, GPU-327 enables imaging of deeper ischemia, such as choroidal circulation. Additionally, from an electroretinogram, GPU-327 did not cause neurotoxicity. GPU-327 identified hypoxic area both in vivo and in vitro.

Novel PAMAM Dendron as a Bichromophoric Probe Based on Rhodamine 6G and 1,8-Naphthalimide.

A novel PAMAM dendron designed as a wavelength-shifting bichromophore with 1,8-naphthalimide energy "donor" capable of absorbing light and efficiently transferring the energy to a focal Rhodamine 6G "acceptor" was synthesized and investigated. Moreover, the system was configured on the "fluorophore-spacer-receptor" format. Thus, the distinguishing features of FRET systems were successfully combined with the properties of photoinduced electron transfer and classical ring-opening sensor systems. The synthesized compound shows excellent signaling properties towards protons, Hg(2+) and Fe(3+) ions, therefore, the system is able to act as an one-output combinatorial logic circuit with four chemical inputs.

Self and directed assembly: people and molecules.

Self-assembly and directed-assembly are two very important aspects of supramolecular chemistry. As a young postgraduate student working in Canada with Tom Fyles my introduction to Supramolecular Chemistry was through the self-assembly of phospholipid membranes to form vesicles for which we were developing unimolecular and self-assembling transporter molecules. The next stage of my development as a scientist was in Japan with Seiji Shinkai where in a “Eureka” moment, the boronic acid templating unit (directed-assembly) of Wulff was combined with photoinduced electron transfer systems pioneered by De Silva. The result was a turn-on fluorescence sensor for saccharides; this simple result has continued to fuel my research to the present day. Throughout my career as well as assembling molecules, I have enjoyed bringing together researchers in order to develop collaborative networks. This is where molecules meet people resulting in assemblies worth more than the individual “molecule” or “researcher”. My role in developing networks with Japan was rewarded by the award of a Daiwa-Adrian Prize in 2013 and I was recently rewarded for developing networks with China with an Inaugural CASE Prize in 2015.

ChemInform Abstract: Self and Directed Assembly: People and Molecules

AbstractReview: [124 refs.