Efficient Photoinduced Electron Transfer Research Articles

Photoexcitation-Assisted Molecular Doping for High-Performance Polymeric Thermoelectric Materials.

Molecular doping plays a crucial role in modulating the performance of polymeric semiconductor (PSC) materials and devices. Despite the development of numerous molecular dopants and doping methods over the past few decades, achieving highly efficient doping of PSCs remains challenging, primarily because of the inadequate matching of frontier energy levels between the host polymers and the dopants, which is critical for facilitating charge transfer. In this work, we introduce a novel doping method termed photoexcitation-assisted molecular doping (PE-MD), capable of transcending limitations imposed by energy level disparities through the mediation of efficient photoinduced electron transfer between polymers and dopants. This approach significantly amplifies the electrical conductivity of the PDPP4T polymer, increasing it by more than 4 orders of magnitude to a maximum value of 349.67 S cm-1. Given that only the irradiated region experiences a substantial increase in doping level, the PE-MD process facilitates the photoresist-free and precise patterning of doped polymers at a resolution down to 1 μm. Furthermore, the enhanced electrical conductivity of the photoexcitation-assisted molecularly doped PDPP4T film promotes efficient thermoelectric conversion, yielding an impressive initial power factor of 226.1 μW m-1 K-2 and a figure-of-merit (ZT) of 0.18, accompanied by improved thermal and ambient stability. The PE-MD strategy not only remarkably elevates the doping level of PSCs toward efficient thermoelectric conversion but also preserves the easy processability of flexible and integrated devices.

Type II photoinitiators with collagen-based cyanine for cell encapsulation under green-red LED

3D bioprinting with cell-laden materials is an emerging technique for fabricating functional tissue constructs. However, current cell-laden bioinks often lack sufficient cytocompatibility with commonly used UV-light sources. In this study, green to red photoinduced hydrogel crosslinking was obtained by introducing synthesized biosafety photoinitiators and used in light-based direct ink writing (DIW) 3D printing for enabling cell encapsulation successfully. The novel type II photointiators contain iodonium (ONI) and synthesized cyanine dyes CZBIN, TDPABIN, Col-SH-CZ, and Col-SH-TD with strong absorption in the range of 400–600 nm. Collagen-based macromolecule dyes Col-SH-CZ and Col-SH-TD showed excellent cytocompatibility. The photochemistry of these photoinitiators revealed an efficient photoinduced electron transfer (PET) process from the singlet excited states of the dyes to iodonium (ONI), facilitating the crosslinking of the biogels. L929 cells were encapsulated in Gel-MA hydrogels containing various photoinitiating systems and exposed to near-ultraviolet, green, or red LED irradiation. DIW-type 3D printing of Gel-MA bioink with L929 cells was also evaluated. The cell viability achieved with green light encapsulation reached 90 %. This novel approach offers promising prospects for bioprinting functional tissues with enhanced cytocompatibility under visible light conditions.

Surface-Grafted Single-Atomic Pt-Nx Complex with a Precisely Regulating Coordination Sphere for Efficient Electron Acceptor-Inducing Interfacial Electron Transfer.

Based on the electron-withdrawing effect of the Pt(bpy)Cl2 molecule, a simple post-modification amide reaction was firstly used to graft it onto the surface of NH2-MIL-125, which performed as a highly efficient electron acceptor that induced the conversion of the photoinduced charge migration pathway from internal BDC→TiOx migration to external BDC→PtNx migration, significantly improving the efficiency of photoinduced electron transfer and separation. Furthermore, precisely regulating over the first coordination sphere of Pt single atoms was achieved using further post-modification with additional bipyridine to investigate the effect of Pt-Nx coordination numbers on reaction activity. The as-synthesized NML-PtN2 exhibited superior photocatalytic hydrogen evolution activity of 7.608 mmol g-1 h-1, a remarkable improvement of 225 and 2.26 times compared to pristine NH2-MIL-125 and NML-PtN4, respectively. In addition, the superior apparent quantum yield of 4.01 % (390 nm) and turnover frequency of 190.3 h-1 (0.78 wt % Pt SA; 129 times compared to Pt nanoparticles/NML) revealed the high solar utilization efficiency and hydrogen evolution activity of the material. And macroscopic color changes caused by the transition of carrier migration paths was first observed. It holds profound significance for the design of MOF-Molecule catalysts with efficient charge carrier separation and precise regulation of single-atom coordination sphere.

Surface‐Grafted Single‐Atomic Pt−Nx Complex with a Precisely Regulating Coordination Sphere for Efficient Electron Acceptor‐Inducing Interfacial Electron Transfer

AbstractBased on the electron‐withdrawing effect of the Pt(bpy)Cl2 molecule, a simple post‐modification amide reaction was firstly used to graft it onto the surface of NH2‐MIL‐125, which performed as a highly efficient electron acceptor that induced the conversion of the photoinduced charge migration pathway from internal BDC→TiOx migration to external BDC→PtNx migration, significantly improving the efficiency of photoinduced electron transfer and separation. Furthermore, precisely regulating over the first coordination sphere of Pt single atoms was achieved using further post‐modification with additional bipyridine to investigate the effect of Pt−Nx coordination numbers on reaction activity. The as‐synthesized NML‐PtN2 exhibited superior photocatalytic hydrogen evolution activity of 7.608 mmol g−1 h−1, a remarkable improvement of 225 and 2.26 times compared to pristine NH2‐MIL‐125 and NML‐PtN4, respectively. In addition, the superior apparent quantum yield of 4.01 % (390 nm) and turnover frequency of 190.3 h−1 (0.78 wt % Pt SA; 129 times compared to Pt nanoparticles/NML) revealed the high solar utilization efficiency and hydrogen evolution activity of the material. And macroscopic color changes caused by the transition of carrier migration paths was first observed. It holds profound significance for the design of MOF‐Molecule catalysts with efficient charge carrier separation and precise regulation of single‐atom coordination sphere.

Ultrasensitive Fluorescence Detection of Ascorbic Acid Using Silver Ion-Modulated High-Quality CdSe/CdS/ZnS Quantum Dots.

Improving the sensitivity of the fluorescence method for the detection of bioactive molecules is crucial in biochemical analysis. In this work, an ultrasensitive sensing strategy was constructed for the detection of ascorbic acid (AA) using high-quality 3-mercaptopropionic acid-capped CdSe/CdS/ZnS quantum dots (MPA-CdSe/CdS/ZnS QDs) as the fluorescent probe. The prepared water-soluble QDs exhibited a high photoluminescence quantum yield (PL QY) of up to 96%. Further, the fluorescence intensity of the QDs was intensively quenched through the dynamic quenching of Ag+ ions due to an efficient photoinduced electron transfer progress. While the existence of AA before adding Ag+ ions, Ag+ ions were reduced. Thus, the interaction of the QDs and Ag+ ions was destroyed, which led to the fluorescence distinct recovery. The detection limit of AA could be as low as 0.2 nM using this sensing system. Additionally, most relevant small molecules and physiological ions had no influence on the analysis of AA. Satisfactory results were obtained in orange beverages, showing its great potential as a meaningful platform for highly sensitive and selective AA sensing for clinical analysis.

Highly effective recognition of Fe3+ and lysine based on hydrosoluble N-doped carbon dots

In this study, dual-color nitrogen-doped carbon dots (NCDs) were synthesized using a simple solvothermal method. These fluorescent NCDs displayed excitation-independent emission in red (598 nm in ethanol) and orange (553 nm in water) due to their effect of two different solvents. Both types of NCDs exhibited high stability under UV irradiation for 80 min. The water-soluble NCDs showed excellent sensitivity to Fe3+ ions by the quenching of their photoluminescent (PL) intensity. Quantitative analysis revealed a gradual decline in PL intensity, with a low detection limit of approximately 0.97 µM. Interestingly, the quenched fluorescence of NCDs caused by Fe3+ could be restored by the addition of lysine to the (NCDs + Fe3+) solution, with an estimated detection limit of about 0.37 µM. This phenomenon could be explained in the terms of non-radiative electron/hole recombination, leading to aggregation through efficient photo-induced electron transfer (PET). Utilizing their high selectivity and sensitivity, these NCDs served as “On-Off-On” switches and were successfully employed for the detection of Fe3+ in real water samples, contributing to environmental safety and control efforts.

Investigation of Interface Characteristics and Physisorption Mechanism in Quantum Dots/TiO2 Composite for Efficient and Sustainable Photoinduced Interfacial Electron Transfer.

Owing to their superior stability compared to those of conventional molecular dyes, as well as their high UV-visible absorption capacity, which can be tuned to cover the majority of the solar spectrum through size adjustment, quantum dot (QD)/TiO2 composites are being actively investigated as photosensitizing components for diverse solar energy conversion systems. However, the conversion efficiencies and durabilities of QD/TiO2-based solar cells and photocatalytic systems are still inferior to those of conventional systems that employ organic/inorganic components as photosensitizers. This is because of the poor adsorption of QDs onto the TiO2 surface, resulting in insufficient interfacial interactions between the two. The mechanism underlying QD adsorption on the TiO2 surface and its relationship to the photosensitization process remain unclear. In this study, we established that the surface characteristics of the TiO2 semiconductor and the QDs (i.e., surface defects of the metal oxide and the surface structure of the QD core) directly affect the QD adsorption capacity by TiO2 and the interfacial interactions between the QDs and TiO2, which relates to the photosensitization process from the photoexcited QDs to TiO2 (QD* → TiO2). The interfacial interaction between the QDs and TiO2 is maximized when the shape/thickness-modulated triangular QDs are composited with defect-rich anatase TiO2. Comprehensive investigations through photodynamic analyses and surface evaluation using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and photocatalysis experiments collectively validate that tuning the surface properties of QDs and modulating the TiO2 defect concentration can synergistically amplify the interfacial interaction between the QDs and TiO2. This augmentation markedly improved the efficiency of photoinduced electron transfer from the photoexcited QDs to TiO2, resulting in significantly increased photocatalytic activity of the QD/TiO2 composite. This study provides the first in-depth characterization of the physical adhesion of QDs dispersed on a heterogeneous metal-oxide surface. Furthermore, the prepared QD/TiO2 composite exhibits exceptional adsorption stability, resisting QD detachment from the TiO2 surface over a wide pH range (pH = 2-12) in aqueous media as well as in nonaqueous solvents during two months of immersion. These findings can aid the development of practical QD-sensitized solar energy conversion systems that require the long-term stability of the photosensitizing unit.

Interface engineering in a nitrogen-rich COF/BiOBr S-scheme heterojunction triggering efficient photocatalytic degradation of tetracycline antibiotics

Tetracycline (TC) antibiotics, extensively utilized in livestock farming and aquaculture, pose significant environmental challenges. Photocatalysis, leveraging renewable sunlight and reusable photocatalysts, offers a promising avenue for mitigating TC pollution. However, identifying robust photocatalysts remains a formidable challenge. This study introduces a novel hollow-flower-ball-like nanoheterojunction composed of a nitrogen-rich covalent organic framework (N-COF) coupled with BiOBr (BOB), a semiconductor with a higher Fermi level. The synthesized N-COF/BOB S-scheme nanoheterojunction features an expanded contact interface, strengthened chemical bonding, and unique band topologies. The N-COF/BOB composites showcased exceptional TC degradation performance, achieving an 81.2% removal of 60 mg/L TC within 2 h, markedly surpassing the individual efficiencies of N-COF and BOB by factors of 3.80 and 5.96, respectively. Furthermore, the total organic carbon (TOC) removal efficiency highlights a superior mineralization capacity in the N-COF/BOB composite compared to the individual components, N-COF and BOB. The toxicity assessment revealed that the degradation intermediates possess diminished environmental toxicity. This enhanced performance is ascribed to the robust S-scheme nanoheterojunction structure, which promotes efficient photoinduced electron transfer from BOB to N-COF. This process also augments the separation of photogenerated charge carriers, resulting in an increased yield of superoxide radicals (∙O2−) and hydroxyl radicals (∙OH). These reactive species significantly contribute to the degradation and mineralization of TC. Consequently, this study introduces a sustainable approach for addressing emerging antibiotic contaminants, employing COF-based photocatalysts.

Construction of two-dimensional fluorescent covalent organic framework nanospheres for the detection and removal of tetracycline

The abuse of tetracycline (TCH) leads to a large number of residues in water and agricultural products, which poses a serious threat to the ecological environment and human health. Therefore, it is necessary to develop materials that can simultaneously detect and effectively remove tetracycline. In this paper, we designed and synthesized a two-dimensional fluorescent covalent organic framework nanosphere (ETTA-Nap-COF) for the detection and efficient removal of tetracycline. Due to the efficient photoinduced electron transfer (PET) between ETTA-Nap-COF and TCH, a significant fluorescence enhancement of the COF material could be observed in the presence of TCH under UV light illumination, thereby realizing a selective and sensitive fluorescence sensing of tetracycline. At the same time, the combination of π-π stacking and the porous network structure of ETTA-Nap-COF is conducive to the efficient adsorption and removal of tetracycline, and the maximum adsorption capacity can reach 457.72 mg/g. The ETTA-Nap-COF material has good recyclability and high structural stability. Our work provides a new research idea for fluorescence detection and efficient removal of tetracycline.

Meso-aryltellurium-BODIPY-based fluorescence turn-on probe for selective, sensitive and fast glutathione sensing in HepG2 cells

Glutathione (GSH) as one most abundant thiol, acts as important roles in regulating cellular redox activities, and various diseases are closely related with its abnormal levels. Thus, monitoring intracellular GSH levels is essential for understanding cellular metabolism of many related diseases. In this work, we firstly reported a new fluorescence turn-on sensor, which was capable of selectively, sensitively and rapid sensing GSH over other thiols, especially cysteine and homocysteine in solutions and living cells. A meso-aryltellurium boron dipyrromethene (BODIPY) was firstly designed and synthesized, which showed silenced emission due to an efficient photoinduced electron transfer (PET) process from electron-rich Te to BODIPY, and then upon exposure to GSH, the meso-Te-C bond could be rapidly cleaved by the thiol group of GSH, thus resulting in an obvious fluorescence “turn-on” phenomenon through inhibition of the PET effect. This probe exhibited excellent selectivity and sensitivity towards GSH with a short response time of 2 min, showing a remarkable fluorescence enhancement observed at 541 nm with a large fluorescence quantum yield increase from nearly 0 to 0.73 upon excitation at 500 nm in PBS/CH3CN (9/1, v/v). The detection limit towards GSH was further calculated to be 1.7 nM by the linear fluorescence change at 541 nm in the GSH-concentration ranging from 0 to 4 μM. Furthermore, its sensing mechanism was validated by using mass spectrometry, confirming the rapid cleavage of the Te–C bond by GSH. Finally, cell imaging experiments demonstrated that this probe could successfully detect GSH in living cells, highlighting its potential for rapid and sensitive detection of intracellular GSH level changes. Therefore, a new meso-aryltellurium-BODIPY fluorescence turn-on sensor was firstly developed, which could selectively, sensitively and fast detect cellular GSH over other thiols based on the rapid cleavage of the meso Te–C bond.

γ-graphynes with extended polyyne chains for efficient photoinduced electron transfer in complexes with fullerenes

In recent years, much attention has been paid to γ-graphynes due to their high potential in practical applications. The unique combination of sp2–sp carbon atoms, an extended π-conjugated structure and evenly distributed dehydrobenzo[n]annulene pores provide excellent performance of γ-graphynes in gas separation, water purification, sensors, and catalysis. In this work, we report the ground and excited state properties of γ-graphyne, γ-graphdiyne, and γ-graphtriyne and their non-covalent complexes with fullerenes. Our results demonstrate that the non-covalent complexes are stable and exhibit low mobility of C60 across the graphtriyne sheet. The electron-withdrawing ability of these materials is enhanced by passing from γ-graphyne to γ-graphtriyne, which assists in photoinduced electron transfer from endohedral fullerenes to graphyne. The process is found to occur on a sub-nanosecond time scale in the complexes of γ-graphdiyne and γ-graphtriyne with Sc3N@C80. These theoretical results provide useful insights for the development of carbon materials for photovoltaic applications.

Efficient persulfate activation by photo-excited organic dyes: Mechanism and application for actual dyeing wastewater self-purification

Sulfate Radical-Advanced Oxidation Processes are considered an efficient way for purifying dyeing wastewater, which commonly resists conventional treatment processes owing to the complex components, low biodegradability and high toxicity. However, this emerging technique is associated with issues of secondary pollution and great energy consumption during peroxymonosulfate (PMS) or persulfate (PS) activation processes. Herein, a dye pollutant/PS/visible light self-catalytic system was constructed, based on the photosensitive property of organic dyes for PS activation without catalyst and energy input. In this system, the degradation ratio of 100 mL 10 mg L−1 basic fuchsin, rhodamine B and eosin Y significantly increased by 60%, 76% and 50%, compared with the process without light irradiation. Such improvements were attributable to an efficient photo-induced electron transfer from photo-excited dyes to PS, which has the precondition that the lowest unoccupied molecular orbital (LUMO) energy level of the dye is higher than that of PS, thereby generating oxidizing species like ·SO4−, ·OH and 1O2 for pollutants degradation. Due to the high performance of pollutants simultaneous removal, wide pH adaptability and anti-interference, the complex self-catalytic system consisted of nine dyes and bis-phenol A exhibited the possibility for practical application. Expectedly, the actual dyeing wastewater self-purification system featured a decolorization efficiency of 54% accompanied by the removal of co-existing aromatic proteins and tryptophan-like substances; moreover, the acute bio-toxicity of the raw wastewater greatly decreased by 61.6%. Owing to its high efficiency, eco-friendliness and low consumption, the constructed “using waste to treat waste” system provides a promising way for wastewater treatment.

Non-Conjugated Bis-(Dithienylethene)-Naphthalenediimide as a Dynamic Anti-Counterfeiting Agent: Driving the Wheel of Photoswitching Enactment.

Photochromic fluorescent molecules dramatically extend their fields of applications ranging from optical memories, bioimaging, photoswitches, photonic devices, anti-counterfeiting technology and many more. Here, we have logically designed and synthesized a triazole appended bis-(dithienylethene)-naphthalenediimide based photo-responsive material, 5, which demonstrated fluorescence enhancement property upon photocyclization (ΦF =0.42), with high photocyclization (44 s, ksolution =0.0355 s-1 , ksolid =0.0135 s-1 ) and photocycloreversion (160 s, ksolution =0.0181 s-1 , ksolid =0.0085 s-1 ) rate and decent photoreaction quantum yield (Φo→c =0.93 and Φc→o =0.11). The open isomer almost converted to the closed isomer at photo-stationary state (PSS) with distinct color change from colorless to blue with 92.85 % conversion yield. A reversible noninvasive modulation of fluorescence through efficient photoinduced electron transfer (PET) process was observed both in solution as well as in solid state. The fluorescence modulation through PET process was further corroborated with thermodynamic calculations using the Rehm-Weller equation and quantum chemical studies (DFT). The thermally stable compound 5 exhibits high fatigue resistance property (up to 50 cycles) both in solution and solid state. Furthermore, the compound 5 was successfully applied as erasable ink and in deciphering secret codes (Quick Response/bar code) portending potential promising application in anti-counterfeiting.

Impact of Non-Covalent Interactions of Chiral Linked Systems in Solution on Photoinduced Electron Transfer Efficiency.

It is well-known that non-covalent interactions play an essential role in the functioning of biomolecules in living organisms. The significant attention of researchers is focused on the mechanisms of associates formation and the role of the chiral configuration of proteins, peptides, and amino acids in the association. We have recently demonstrated the unique sensitivity of chemically induced dynamic nuclear polarization (CIDNP) formed in photoinduced electron transfer (PET) in chiral donor-acceptor dyads to non-covalent interactions of its diastereomers in solutions. The present study further develops the approach for quantitatively analyzing the factors that determine the association by examples of dimerization of the diastereomers with the RS, SR, and SS optical configurations. It has been shown that, under the UV irradiation of dyads, CIDNP is formed in associates, namely, homodimers (SS-SS), (SR-SR), and heterodimers (SS-SR) of diastereomers. In particular, the efficiency of PET in homo-, heterodimers, and monomers of dyads completely determines the forms of dependences of the CIDNP enhancement coefficient ratio of SS and RS, SR configurations on the ratio of diastereomer concentrations. We expect that the use of such a correlation can be useful in identifying small-sized associates in peptides, which is still a problem.

Solid-State Luminescence Turn-On Sensing Using MOF-Confined Reporter-Spacer-Receptor Architectures Facilitated by Quencher Displacement.

The reporter-spacer-receptor (RSR) approach is prevalent to develop molecular turn-on sensors. However, the fluorescent RSR sensors barely operate in solid state, which hinders their fabrication into devices for practical applications. Herein, we present a novel strategy to achieve solid-state luminescence turn-on sensing by assembling RSR architectures within MOF frameworks. Unlike the regular RSR systems, the framework-confined fluorophore and receptor are well arranged and separated even in the solid state. This concept is illustrated by a multicomponent MOF (Fc@NU-1000), which contains organic linkers with a highly luminescent pyrene core as the reporter, Zr6 nodes with unsaturated sites as the receptor, and the incorporated Fc molecules as the quencher. The separate incorporation of pyrene core and Fc in the multicomponent MOF favors an efficient pseudointramolecular photoinduced electron transfer (PET) process, resulting in significant luminescence quenching. Interestingly, such PET process can be blocked via the quencher displacement initiated by the phosphate analyte, therefore recovering the solid-state luminescence of MOF microcrystals. We found that Fc@NU-1000 is shown as a sensitive solid-state luminescence turn-on probe for phosphate with the naked-eye response at a low content. What's more, this study is the first example of confining a quencher displacement-based RSR system in the MOF framework for solid-state luminescence turn-on sensing, thus also providing new opportunities for MOF materials to develop luminescence turn-on sensors.

Excellent Nonlinear Optical Limiting Behavior of Tetra (C60) Lanthanum Phthalocyanine in Solid Poly(methyl methacrylate) Films

This work reports on the exceptional optical limiting performance of a novel D–A-type compound, namely, LaPc-4(C60), wherein the lanthanide phthalocyanine is used as a donor and four C60 are used as acceptors. In addition, phenyl ether bonds were introduced into the molecule, making it semirigid and increasing its solubility. At the same time, the phenyl ether bond could act as a π-electron bridge, which increases the electron transfer pathway, expands the π-conjugated system, and reduces the spatial site resistance of the molecule. Furthermore, the uniform poly(methyl methacrylate) (PMMA) composite film (LaPc-4(C60)/PMMA) was prepared by a simple solution casting method. In comparison with individual C60 or LaPc(CHO)4, both LaPc-4(C60) in solution and in the solid PMMA composite film exhibited larger third-order nonlinear absorption coefficients and lower limiting thresholds at 532 nm. In particular, LaPc-4(C60)/PMMA exhibits huger nonlinear absorption coefficient (2900 cm/GW) and larger third-order susceptibility (4.91 × 10–9 esu), which can be attributed to the synergistic effect of the different non-linear absorption mechanisms and efficient photoinduced electron transfer process between C60 and LaPc.

Charge-Separated States Determined Photoinduced Electron Transfer Efficiency in a D-D-A System in an External Electric Field

Focusing on the photoinduced electron transfer properties of the D-D-A molecule ((TPA-TT)-BODIPY-C60) in an external electric field (Fext), the excited-state properties in which the double-donor molecule is excited to form three charge-separated states were simulated. The charge-transfer processes of these three charge-separated states were investigated by considering the two donors as a whole ((TPA-TT-BODIPY)·+-C60·–) as a comparison object. The electronic coupling (VDA), reorganization energy (λ), and free energy (ΔG) of the different charge-separated states in Fext were calculated and simulated. The calculated results show that the λ of (TPA-TT-BODIPY)·+-C60·– ranges from 0.576 to 0.51 eV, and the calculated ΔG of exciton dissociation ranges from −1.402 to −1.143 eV, indicating that exciton dissociation occurs in the Marcus inverted region. In the range of Fext = −10 × 10–5 to 10 × 10–5 au, the trend of the charge-transfer rate is gradually increasing, and the rate increase is mainly from the VDA and ΔG changes. Moreover, the rapid formation of the (TPA-TT)-BODIPY·+-C60·– charge-separated state and the formation of the long-lived (TPA-TT)·+ -BODIPY-C60·– are indicated by the exciton dissociation rate. By studying the charge-transfer parameters under different electric field directions, it is found that the regulation of electric field strength on the charge-transfer rate is consistent. These results provide a feasible method for the rational design of a new type of electron transfer process with high efficiency of the D-D-A system.

Fluorometric Detection of Al3+ Ion in Mixed Aqueous Solvent Based on Simple Schiff-Base Molecular Prob

A simple fluorometric detection for Al3+ ion in mixed aqueous medium using a simple Schiff-base molecule through PET mechanism is discussed. The di-phenolic Schiff-base molecule (EAMHM) was synthesized by the condensation reaction of multiple phenolic aldehyde molecules with a diamine containing multiple aldehyde-reacting primary amine moieties. The extremely low fluorescence quantum yield for EAMHM is highly useful for the off-mode of fluorescence sensing purposes. Contrary to various other cations Ni2+, Mg2+, Co2+, Cu2+, Zn2+, Cr3+, Cd2+, Fe3+, Ba2+, Hg2+, the selective Al3+ ion induced large fluorescence enhancement can be employed to detect Al3+ even in the presence other bi- or tri-valent cations. Moreover, linear change in fluorescence intensity with Al3+ concentration is highly beneficial for ratiometric detection of unknown Al3+ concentrations. As revealed from various spectroscopic and theoretical calculations, EAMHM forms a 1:1 complex with Al3+ showing a large increase in fluorescence intensity. It has also been identified that efficient photo-induced electron transfer (PET) in free EAMHM is mainly responsible for its low fluorescence intensity, whereas the removal of such PET process during its complexation with Al3+ produces large fluorescence enhancement. The structural and electronic parameters of the free EAMHM and EAMHM-Al3+ complex have been analyzed using DFT-based theoretical calculations.

A Novel Electron Donor‐Acceptor Carbazole‐Zn(II)Phthalocyanine – Perfluorinated Subphthalocyanine Conjugate: Synthesis, Characterization, and Photoinduced Electron‐Transfer

AbstractPorphyrinoids are considered perfect candidates for the preparation of model electron donor‐acceptor (D‐A) systems as they enable fast and efficient photoinduced electron transfer. Herein, we report on the synthesis and photophysical characterization of a ZnPc−SubPc conjugate covalently connected through a short‐range alkyne spacer. We designed and prepared the conjugate, which comprise, on the one hand, a perfluorinated SubPc with strong electron acceptor character and, on the other, a Pc peripherally functionalized with carbazoles with strong electron donor character. Photoinduced electron transfer events are in‐depth analyzed by several techniques, including steady‐state absorption, time‐resolved emission and transient absorption measurements on different time scales. Our studies confirm a full charge separation occurring from a photoexcited charge transfer state.

Thermal annealing-boosted photoinduced electron transfer efficiency of g-C3N4/Au NPs hybrids for promoting SERS detection of uric acids

As for the ultrasensitive diagnosis of biomolecules via surface-enhanced Raman scattering spectroscopy (SERS), the primary requirement is to effectively enhance the activity of nano-substrates. Herein, we report an interesting strategy for further boosting SERS activity by thermal annealing treatment of as-prepared hybrid substrates. Initially, highly dense and monodisperse plasmonic Au nanoparticles (NPs) were loaded on two-dimensional (2D) graphitic carbon nitride (g-C3N4) nanosheets. By adopting uric acids (UAs) as probe biomolecules, the g-C3N4/Au NPs with appropriate ~2.1% Au compositions exhibit much higher Raman signals than that of the hybrids with other Au contents. Besides the enhancement by routinely controlling hybrid components, the further maximizing SERS activity with a ~2.6-fold improvement than the original one can be obtained by thermal annealing of g-C3N4/Au NPs at 350 ℃ condition. It enables the thermal modified g-C3N4/Au NPs to be applied for highly sensitive monitoring of UAs in artificial urine. The corresponding detection limit is achieved at the ultralow level of 10−11 M, which is nearly two orders of magnitude better than that of the unannealed sample. It should be attributed to the stronger synergistic coupling effect by thermal annealing treatment that gives rise to the higher-efficiency photoinduced electron transfer (PIET) between g-C3N4 supports and plasmonic Au NPs. The present work provides a new opportunity for further promoting the SERS activity of prefabricating nano-substrates, holding great potential for practical monitoring of ultra-trace biomolecules in the near future.