Photoinduced Electron Transfer Process Research Articles

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.

Imidazole appended rotatable hydroxy quinoline scaffold as dual signaling fluorescent chemosensor: Detection of silver ions with hypsochromic shift and hydroxide ions with bathochromic shift and their LFP’s, anticounterfeiting, soil analysis and bio-imaging

An imidazole conjugated hydroxy quinoline based chemosensor (QBI) was developed for the specific dual detection of silver (Ag+) and hydroxide (OH−) ions by fluorimetric technique. QBI had weak fluorescent emission, upon binding with Ag+ and OH−, fluorescence intensity enhanced with a large hypsochromic shift for Ag+ ion and notable bathochromic shift for OH− ions respectively. Three modes of possible mechanistic pathways accounts for the detection of the Ag+ ions, restriction of the C–C free rotation between the quinoline and imidazole scaffolds, blocking of photoinduced electron transfer (PET) process assisted by the Intramolecular charge transfer (ICT) process. On other hand, the –OH moiety of QBI gets deprotonated during the process of detecting OH− ions. The binding stoichiometry of complexations was confirmed by Jobs plot, Benesi-hildebrand, 1H NMR titration, DFT analysis and ESI-TOF. The limit of detection (LOD) of QBI with Ag+ and OH− was found to be 3.53 × 10−8 M for Ag+ and 1.5 × 10−7 M respectively. Latent fingerprintvisualization (LFP), anti-counterfeiting applications, and soil analysis are merely a few instances of where QBI has been effectively put to use in the real world for the specific detection of Ag+ and OH− ions. Furthermore, receptor QBI was utilized in bacterial imaging against E.coli and pseudomonas pathogens for the detection of both ions.

A coumarin hydrazone appended rotatable phenolic scaffold as fluorescent chemosensor for Ag+ ions and its bio imaging applications

A coumarin hydrazone-phenol conjugate, COH4 was designed, synthesized and utilized for the cation sensing studies by fluorimetry studies. The synthesized chemosensor was completely characterized by the usual spectroscopic and analytical studies. The COH4 receptor was examined for the detection of metal ions, in which it had a noticeable blue shifted fluorescence enhancement for Ag+ ions. Upon binding towards Ag+ ions, the photoinduced electron transfer (PET) process is inhibited via intramolecular charge transfer (ICT) process assisted by the arrest of the carbon–carbon single bond rotation. The binding stoichiometry of COH4 + Ag+ complexation ratio is noted to be 1:2, which was further confirmed by jobs plot method. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.41 µM and 0.13 µM respectively. Moreover, COH4 was successfully utilized for the practical applications of Ag+ ion detection in bacterial cell lines.

Experimental and Theoretical Studies of Fluorescent "Turn Off" Sensor Functionalized With Carboxylic Acid and Naphthalene Group for Selective Detection of 2,4,6-Trinitrophenol.

A fluorescent sensor, 5-((2-hydroxynaphthalen-1-yl)methyleneamino)benzene-1,3-dicarboxylic acid (coded as SB), containing both π-π interacting sites (such as π-electron-rich moieties) and hydrogen bonding (H-bonding) interacting sites (such as highly acidic protons) has been developed via high yield reflux method. It was characterized by the various analytical techniques such as Fourier transform-infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (1H-NMR), thermogravimetric analysis (TGA), field emission scanning electron microscope (Fe-SEM), elemental mapping, and UV - visible spectroscopy etc. The spectral response of the as-synthesized SB sensor has been investigated for various nitro explosives (NEs). It has been found that the SB sensor selectively and sensitive sense highly toxic 2,4,6-trinitrophenol (TNP) via the "turn-off" quenching response. Its limit of detection for TNP was calculated to be 30 ppb. Spectral overlap, detailed mechanistic studies for their mode of action, and density functional theory (DFT) calculations reveals that photo-induced electron transfer process (PET), fluorescence energy transfers process (FRET), and electrostatic interactions (i.e. H-bonding) are the key factors for the turn-off response of SB towards TNP. Notably, the synthesis of the sensor is cost-effective, energy efficient, and economic.

A Quenched Fluorescence‐based Assay for Selective Detection of Nitroaromatic Compounds using Pyrene‐Appended Oxacalix[4]arene Host

AbstractA novel pyrene appended supramolecular assembly (PAOC) has been fabricated by reacting intermediate‐pyren‐1‐ylmethyl 2‐chloroacetate (PMCA) with oxacalix[4]arene and characterized by 1H NMR, 13 C NMR and ESI‐Mass. PAOC works as fluorescent chemosensor for the selective detection of nitroaromatic compounds such as 4‐nitrophenol (4NP) and 2,4,6‐trinitrophenol (TNP). The binding mechanism between PAOC and the analytes were investigated through various spectroscopic techniques, and the results indicate a strong interaction between the two. The fluorescence intensity of PAOC is quenched upon interaction with nitroaromatic compounds due to a photoinduced electron transfer process, which was validated by DFT calculations. The sensor exhibits excellent selectivity and sensitivity towards TNP over other nitroaromatic compounds. The detection limits for TNP and 4NP were found to be 1.6 μM and 1.9 μM, respectively. PAOC's detection results in real water samples are remarkable. This study provides a new approach to develop highly selective and sensitive chemosensor for the detection of nitroaromatic compounds, which have significant environmental and health hazards.

Investigating Design Rules for Photoinduced Electron Transfer Quenching in Triangulenium Probes.

Fluorescent probes based on photoinduced electron transfer (PET) quenching of long lifetime triangulenium fluorophores have found multiple applications. For such probes a successful design relies on the right balance between the rates of PET quenching and fluorescence. In a series of ADOTA (A) and DAOTA (D) triangulenium fluorophores appended with aniline-like quencher moieties, we have investigated the rates of quenching and its relation to thermodynamic driving force, distance, and conjugation within the quencher moiety. Three different quenchers, a short (1), a long (2), and a long twisted (3), 4-aminophenyl, 4'-aminobiphenyl, and 2,2'-dimethyl-4'-aminobiphenyl, respectively were investigated. Time-resolved fluorescence measurement was used to measure PET rate constantkPETranging from >4x1011s-1to 2x109s-1. Interestingly, PET quenching is equally efficient/fast from1and2, even with increase in distance between the donor and the acceptor. However, when twisting the biphenyl in3, a 20-fold decrease in quenching is found. Even with the decrease inkPETthe quenching in3A/Dis still highly efficient, with nearly 99% quenching. The study show that long lifetime fluorophores can be efficiently switched even by relative slow PET processes and that PET quencher moieties can be removed far from the fluorophore if conjugated linkers are applied.

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.

Induction of chirality in the charge transfer complex photochemistry

Electron donor and acceptor undergo association in solution to form a weak molecular complex, namely a charge transfer complex. The formation of the complex is apparent by its new low-energy absorption band. Upon photoexcitation of this charge transfer band, an intracomplex electron transfer is facilitated to form a contact ion radical pair. The theoretical basis for the complex formation and the subsequent photoinduced electron transfer process has been well established already half a century ago. Nevertheless, the charge transfer complex photochemistry is now in a renaissance, due to its synthetic utility of its radical ion pair. By intentionally sidestepped unproductive back electron transfer process, a desired product is effectively obtained with or without external reagent and/or catalyst. In addition, the photoexcitation of the complex does not require any additional photocatalyst and often conceivable with the visible light. Accordingly, various donor/acceptor pairs and synthetic applications have been emerged as novel photoreaction systems in the last two decades. Some have also addressed the stereoselective transformations. This mini review highlights the recent progress of the asymmetric photoreaction, in particular in synthetic applications, based on the photoexcitation of the charge transfer complex, in comparison with photoredox catalysis.

Less is better: Insight into the concentration dependency of the photoreduction of Eu3+ in Ba2SiO4

Photoinduced electron transfer processes in luminescent materials drive numerous applications like medical imaging, ionizing radiation dosimetry and safety signage. However, the concentration dependency of the photoreduction of the dopants during this process is still poorly understood. Here, optical spectroscopy and electron paramagnetic resonance (EPR) experiments are systematically performed to reveal the doping concentration-dependent photoreduction behavior in Ba2-xEuxSiO4 where a fraction of the Eu3+ dopants can be reduced to Eu2+ upon irradiation with X-rays. EPR measurements show that the conversion ratio of Eu3+→Eu2+ decreases with increasing concentration at the same irradiation dose, resulting in the concentration dependency of the photoreduction behavior in Ba2-xEuxSiO4. Optical spectroscopy measurements show that although the incorporated Eu3+ ions occupy at least three crystallographic sites, Eu3+ can only be photoreduced on one of these sites. Meanwhile, the relative occupancy of this photoreducible site decreases as the doping concentration increases. The combination of these two factors might be responsible for the decreased conversion ratio of Eu3+→Eu2+ as the doping concentration increases. These findings provide insights into the photoreduction of dopants in luminescent materials and can facilitate the exploration of this functional behavior for advanced devices.

Construction of porous ZnS/TiO2 S-scheme heterostructure derived from MOF-on-MOF with boosting photocatalytic H2-generation activity

The development of photocatalysts with synergistic effects is a crucial step in improving the utilization of clean energy for hydrogen generation. In this study, a novel porous ZnS/TiO2 heterostructure was successfully fabricated through the sulfuration of ZIF-8/NH2-MIL-125(Ti) using a one-pot hydrothermal method. Under simulated solar light, the as-prepared ZnS/TiO2 (5:1) heterostructure exhibited enhanced photocatalytic hydrogen production with a rate of 1718 μmol h−1 g−1, which is 4.8 times of ZnS and 38.8 times of TiO2, respectively. The construction of a S-scheme heterojunction between ZnS and TiO2 can enhance electron transfer and suppress electron-hole recombination, which is crucial for efficient photocatalysis. The photoelectrochemical test results were analyzed in detail to understand the photoinduced electron transfer process and the proposed photocatalytic mechanism. This work has significant potential for enhancing the solar hydrogen production performance of MOFs-derived heterojunction photocatalysts, providing a promising approach for clean energy generation.

Superassembly of 4-Aminothiophenol-Modified Mesoporous Titania-Alumina Oxide Heterochannels for Smart Ion Transport Based on the Photo-Induced Electron-Transfer Process.

Light-responsive nanochannels have attracted extensive attention due to their noninvasive external field control and intelligent ion regulation. However, the limited photoresponsive current and the low photoelectric conversion efficiency still restrict their development. Here, a light-controlled nanochannel composed of 4-aminothiophenol and gold nanoparticles-modified mesoporous titania nanopillar arrays and alumina oxide (4-ATP-Au-MTI/AAO) is fabricated by the interfacial super-assembly strategy. Inspired by the process of electron transfer between photosystem I and photosystem II, the efficient electron transfer between TiO2, AuNPs, and 4-ATP under light is achieved by coupling the photoresponsive materials and functional molecules. Under illumination, 4-ATP is oxidized to p-nitrothiophenol (PNTP), which brings about changes in the wettability of the nanochannel, resulting in significant improvement (252.8%) of photoresponsive current. In addition, under the action of the reductant, the nanochannels can be restored to the initial dark state, enabling multiple reversible cycles. This work opens a new route for the fabrication of high-performance light-controlled nanochannels by coupling light-responsive materials and light-responsive molecules, which may guide the development of photoelectric conversion nanochannel systems.

Photo-induced Electron Transfer-triggered Structure Deformation Promoting Near-Infrared Photothermal Conversion for tumor therapy.

Photothermal therapy (PTT) is a promising approach to cancer treatment. Heptamethine cyanine (Cy7) is an attractive photothermal reagent because of its large molar absorption coefficient, good biocompatibility, and absorption of near-infrared irradiation. However, the photothermal conversion efficiency of Cy7 is limited without ingenious excitation-state regulation. In this study, the photothermal conversion ability of Cy7 is efficiently enhanced based on photo-induced electron transfer (PET)-triggered structural deformation. Three Cy7 derivatives, whose Cl is replaced by carbazole, phenoxazine, and phenothiazine at the meso-position (CZ-Cy7, PXZ-Cy7, and PTZ-Cy7), are presented as examples to demonstrate the regulation of the energy release of the excited states. Because the phenothiazine moiety exhibits an obvious PET-induced structural deformation in the excited state, which quenches the fluorescence and inhibits intersystem crossing of S1 →T1 , PTZ-Cy7 exhibits a photothermal conversion efficiency (PCE) as high as 77.5%. As a control, only PET occurs in PXZ-Cy7, with a PCE of 43.5%. Furthermore, the PCE of CZ-Cy7 is only 13.0% because there is no PET process. Interestingly, PTZ-Cy7 self-assembles into homogeneous nanoparticles exhibiting passive tumor-targeting properties. This study provides a new strategy for excited-state regulation for photoacoustic (PA) imaging-guided PTT with high efficiency. This article is protected by copyright. All rights reserved.

A Turn-On Fluorescence Sensor Based on Nitrogen-Doped Carbon Dots and Cu2+ for Sensitively and Selectively Sensing Glyphosate

Glyphosate has excellent herbicidal activity, and its extensive use may induce residue in the environment and enter into humans living through the food chain, causing negative impact. Here, water-soluble 1.55 nm size nitrogen-doped carbon quantum dots (NCDs) with strong blue fluorescence were synthesized using sodium citrate and adenine. The maximum excitation and emission wavelengths of NCDs were 380 nm and 440 nm, respectively. The above synthesized NCDs were first used for the construction of a fluorescence sensor for glyphosate detection. It was found that Cu2+ could quench the fluorescence of NCDs effectively through the photoinduced electron transfer (PET) process, which was confirmed using fluorescence lifetime measurements. Additionally, the fluorescence was restored with the addition of glyphosate. Hence, a sensitive turn-on fluorescence sensor based on NCDs/Cu2+ for glyphosate analysis was developed. The LODs of glyphosate for water and rice samples were recorded as 0.021 μg/mL and 0.049 μg/mL, respectively. The sensor was applied successfully for ultrasensitive and selective detection of glyphosate in environmental water and rice samples with satisfied recoveries from 82.1% to 113.0% using a simple sample pretreatment technique. The proposed strategy can provide a significant potential for monitoring glyphosate residue in water and agricultural product samples.

Ultrasensitive recognition performance of a folded π-based 1,8-naphthalimide-phthalocyanine fluorescence sensor

Designing ultrasensitive and smart molecules as molecular switches is highly valued in molecular recognition. In this work, a folded π-based molecular switch (NAPC) containing 1,8-naphthalimide and zinc(II) phthalocyanine functional modules was synthesized via cyclo tetramerization of four synthesized 1,8-naphthalimide sensors (NA). The photophysical properties of the folded molecular switch were investigated. This peripherally 1,8-naphthalimide substituted zinc(II) phthalocyanine possessed superior sensitivity in near-infrared “off-on” detection of Al3+, Fe3+, and Cr3+ compared with NA, and the detection limits were calculated to be 0.077 μmol/L for Al3+, 0.073 μmol/L for Fe3+ and 0.067 μmol/L for Cr3+, which were far less than that of NA. Due to the sensitive detection of Fe3+, NAPC was also applied in detecting NO2−. The ultrasensitive recognition mechanism of NAPC was determined to be the level-by-level linkage in the molecule in which the photo-induced electron transfer process in 1,8-naphthalimide sensor module was inhibited by complexing with metal ions first and then caused the inhibition of π-π stacking between two modules. This new folded molecule with a cascade linkage effect has the potential as an excellent fluorescence switch that could be applied in molecular recognition and environmental management.

A thiophene built chalcone as fluorescent chemosensor for silver ions and their applications in strip-paper, ointments, and bio-imaging

A simple thiophene based chalcone as fluorescent receptor (ADC) was synthesized by Claisen Schmidt condensation method upon linking 2-acetyl thiophene (1) and N,N-dimethylamino benzaldehyde (2). The synthesized receptor is well characterized by NMR, IR, and mass spectroscopic techniques. The ADC receptor was examined for the detection of metal ions, in which it had a noticeable blue shifted fluorescence enhancement for Ag+ ions. Upon binding towards Ag+ ions, the photoinduced electron transfer (PET) process is inhibited via intramolecular charge transfer (ICT) process taking place. The binding stoichiometry of ADC + Ag+ complexation ratio is noted to be 2:1, which was further confirmed by jobs plot method, 1H NMR titration, IR spectral analysis, and DFT studies. The limit of detection (LOD) and limit of quantification (LOQ) was found to be 4.98 µm and 6.36 µm respectively. Additionally, ADC showed color changes upon binding with Ag+ ions in strip paper, cotton swab test through UV-365 nm illumination. Moreover, ADC was successfully utilized for the practical applications of Ag+ ion detection in water samples, ointment and bacterial cell lines.

Spectroscopic and TD-DFT studies on the chromo-fluorogenic detection of cyanide ions in organic and aquo-organic media

A new naked-eye chromogenic and fluorogenic probe KS5 has been developed for the detection of CN– ions in neat DMSO and H2O:DMSO (1:1 v/v) media. The probe KS5 exhibited selectivity towards CN– and F− ions in organic and high selectivity towards CN– ions in aquo-organic media resulting in a colour change from brown to colourless and a turn-on fluorescence response. The probe could able to detect CN– ions via a deprotonation process, which was conceived by consecutive addition of hydroxide and hydrogen ions and confirmed using 1H NMR studies. The limit of detection (LOD) of KS5 towards CN– ions were in the range of 0.07–0.62 µM in both these solvent systems. Suppression of intra-molecular charge transfer (ICT) transition and photoinduced electron transfer (PET) process of KS5 by the added CN– ions are responsible for the chromogenic and fluorogenic changes observed, respectively. Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) calculations strongly supported the proposed mechanism along with the optical properties of the probe before and after the addition of CN– ions. To prove the practical applicability, KS5 was successfully utilized to detect CN– ions in cassava powder and bitter almonds as well as to determine CN– ions in various real water samples.

Microwave assisted structural engineering on efficient eco-friendly natural dye alizarin for dye sensitized solar cells application

The novel eco-friendly natural dyes, (9E, 10E), − 9, 10-bis(2-(4-nitrobenzylidene) hydrazono) − 9,10 dihydroanthracene-1,2-diol (NHA) have been synthesised using the one-pot microwave-assisted solvent evaporation method, and physicochemical characterizations were carried out using 1H NMR, 13C NMR, GC-MS, and FT-IR data. The photophysical properties of NHA dye were determined using experimental and theoretical techniques. The Stoke’s shift shows a large bathochromic shift in polar solvents, which is due to the π→π * transition. The ground-state optimization of NHA dye was carried out using density functional theory (DFT) with the B3LYP/6–31 G level basis set. The HOMO-LUMO and energy band gap values computed from density functional theory and absorption threshold wavelengths are good agreement with each other. Further, the effect of TiO2 nanoparticles on NHA dye has been studied using spectroscopic and electrochemical techniques. It was observed that, NHA dye showed fluorescence quenching in the presence of TiO2 NPs, which is due to the photo induced electron transfer process. The apparent association constant of the interaction between NHA dye and TiO2 nanoparticles is also calculated using the Benesi-Hildebrand model. The Rehm-Weller relation infers that thermodynamically favourable electron transfer takes place between dyes and TiO2 NPs. Further, the solar cell was constructed using NHA dye as a sensitizer, and the photovoltaic conversion efficiency was found to be 1.16%.

A DFT approach for finding therapeutic potential of graphyne as a nanocarrier in the doxorubicin drug delivery to treat cancer

In the present work, the drug-loading efficacy of graphyne (GYN) for doxorubicin (DOX) drug is investigated for the first time by using density functional theory (DFT). Doxorubicin drug is effective in the cure of numerous types of cancer including bone cancer, gastric, thyroid, bladder, ovarian, breast, and soft tissue cancer. Doxorubicin drug prevents the cell division process by intercalating in the double-helix of DNA and stopping its replication. The optimized, geometrical, energetic, and excited-state characteristics of graphyne (GYN), doxorubicin drug (DOX), and doxorubicin-graphyne complex (DOX@GYN complex) are calculated to see how effective it is as a carrier. The DOX drug interacted with GYN with an adsorption-energy of −1.57 eV (gas-phase). The interaction of GYN with DOX drug is investigated using NCI (non-covalent interaction) analysis. The findings of this analysis showed that the DOX@GYN complex has weak forces of interaction. Charge transfer from doxorubicin drug to GYN during DOX@GYN complex formation is described by charge-decomposition analysis and HOMO-LUMO analysis. The increased dipole-moment (8.41 D) of the DOX@GYN in contrast with therapeutic agent DOX and GYN indicated that the drug will move easily in the biochemical system. Furthermore, the photo-induced electron-transfer process is explored for excited states, and it reveals that upon interaction, fluorescence-quenching will occur in the complex DOX@GYN. In addition, the influence of the positive and negative charge states on the GYN and DOX@GYN is also considered. Overall, the findings indicated that the GYN could be exploited as an effective drug-transporter for the delivery of doxorubicin drug. Investigators will be inspired to look at another 2D nanomaterials for drug transport applications as a result of this theoretical work.

Photochemical Synthesis of Atomically Precise Ag Nanoclusters.

Photochemical methods are effective for controllable synthesis of silver nanoparticles with specific sizes and shapes. Whether they are capable of fabricating Ag nanoclusters (NCs) with atomic precision is yet to be proved. In this work, we synthesize an atomically precise Ag NC, [Ag25(4-MePhC≡C)20(Dpppe)3](SbF6)3 (Ag25), via a process mediated by visible light. Its total structure is determined by X-ray crystallography. The investigation of the mechanism reveals that the formation of Ag25 is triggered by a photoinduced electron-transfer (PET) process. An electron of certain amines is excited by light with wavelength shorter than 455 nm and transferred to Ag+. The amine is oxidized to the corresponding amine N-oxide. Such a PET process is supported by experimental and density functional theory studies. To expand the application scope of the photochemical method, another three NCs, [Ag19(4-tBuPhC≡C)14(Dpppe)3](SbF6)3 (Ag19), [Ag32(4-tBuPhC≡C)22(Dppp)4](SbF6)3 (Ag32), and bimetallic [Ag22Au3(4-tBuPhC≡C)20(Dpppe)3](SbF6)3 (Ag22Au3), are produced by replacing certain ingredients. Furthermore, since the formation of Ag19 can be regarded as a photochromatic process, a facile amine visual detection method is also presented based on this mechanism.

Green Synthesis of Sulfur- and Nitrogen-Doped Carbon Quantum Dots for Determination of L-DOPA Using Fluorescence Spectroscopy and a Smartphone-Based Fluorimeter.

Sulfur- and nitrogen-doped carbon quantum dots (S,N-CQDs) were synthesized using feijoa leaves as a green precursor via a novel route. Spectroscopic and microscopic methods such as X-ray photoelectron spectroscopy, fluorescence spectroscopy, and high-resolution transmission electron microscopy were used to analyze the synthesized materials. The blue emissive S,N-CQDs were applied for qualitative and quantitative determination of levodopa (L-DOPA) in aqueous environmental and real samples. Human blood serum and urine were used as real samples with good recovery of 98.4-104.6 and 97.3-104.3%, respectively. A smartphone-based fluorimeter device was employed as a novel and user-friendly self-product device for pictorial determination of L-DOPA. Bacterial cellulose nanopaper (BC) was used as a substrate for S,N-CQDs to make an optical nanopaper-based sensor for L-DOPA determination. The S,N-CQDs demonstrated good selectivity and sensitivity. The interaction of L-DOPA with the functional groups of the S,N-CQDs via the photo-induced electron transfer (PET) mechanism quenched the fluorescence of S,N-CQDs. The PET process was studied using fluorescence lifetime decay, which confirmed the dynamic quenching of S,N-CQD fluorescence. The limit of detection (LOD) of S,N-CQDs in aqueous solution and the nanopaper-based sensor was 0.45 μM in the concentration range of 1-50 μM and 31.05 μM in the concentration range of 1-250 μM, respectively.