Determination Of Quantum Yield Research Articles

A fiber-optic spectroscopic setup for isomerization quantum yield determination.

A spectroscopic setup for isomerization quantum yield determination is reported. The setup combines fiber-coupled LEDs, a commercially calibrated thermopile detector for measurement of the photon flux, and a fiber-coupled UV-vis spectrometer. By solving the rate equations numerically, isomerization quantum yields can be obtained from the UV-vis absorption spectra. We show that our results for the prototypical photoswitch azobenzene are in excellent agreement with the literature. The analysis of the errors showed that the quantum yields determined using this method are in the same order of magnitude as when using actinometry, thus demonstrating the reliability of our setup.

Photodecarboxylative Ring Annulation of α‐ and β‐Functionalized Phthaloyl‐GABA Derivatives: Bioactive Pyrroloisoindolinones with High Quantum Efficiency

AbstractThe triplet‐sensitized (by the solvent acetone) as well as the direct (λex=300–320 nm) photochemical decarboxylation of N‐phthaloylated γ‐aminobutyric acid (GABA) derivatives are versatile and high‐yielding routes to benzopyrrolizidines via intramolecular electron transfer initiated decarboxylation followed by radical coupling. The ß‐mono‐ and ß,ß'‐disubstituted N‐phthaloyl GABA derivatives 7 a–7 g, respectively, were applied as substrates. Decarboxylative photocyclization yielded hydroxy benzopyrrolizidines 8 a–8 g in high chemical yields and with moderate diastereoselectivities from the ß‐monosubstituted substrates. The analogous α‐substituted GABA derivatives 11 a–11 c were also applied as potential substrates for memory of chirality effects. The reaction quantum yields of the photodecarboxylation reactions for the parent GABA derivative 13 and for the new substrates 7 h and 11 a were determined by the quantum yield determination system (QYDS) and showed a remarkable concentration dependency indicating aggregation at higher substrate concentrations. Inhibition studies on the atherogenic human serine hydrolase cholesterol esterase showed derivatives 8 a and 8 d to exhibit a hyperbolic mode of inhibition with moderate IC50 values of about 60–80 μM.

Novel sunlight-induced monochloramine activation system for efficient microcontaminant abatement

As an eco-friendly and sustainable energy, solar energy has great application potential in water treatment. Herein, simulated sunlight was for the first time utilized to activate monochloramine for the degradation of environmental organic microcontaminants. Various microcontaminants could be efficiently degraded in the simulated sunlight/monochloramine system. The average innate quantum yield of monochloramine over the wavelength range of simulated sunlight was determined to be 0.068 mol/Einstein. With the determined quantum yield, a kinetic model was established. Based on the good agreement between the simulated and measured photolysis and radical contributions to the degradation of ibuprofen and carbamazepine, the major mechanism of monochloramine activation by simulated sunlight was proposed. Chlorine radical (Cl∙) and hydroxyl radical (HO∙) were major radicals responsible for microcontaminant degradation in the system. Moreover, the model facilitated a deep investigation into the effects of different reaction conditions (pH, monochloramine concentration, and water matrix components) on the degradation of ibuprofen and carbamazepine, as well as the roles of the involved radicals. The differences between simulated and measured degradation data of each microcontaminant under all conditions were less than 10 %, indicating the strong reliability of the model. The model could also make good prediction for microcontaminant degradation in the natural sunlight/monochloramine system. Furthermore, the formation of disinfection byproducts (DBPs) was evaluated at different oxidation time in simulated sunlight/monochloramine with and without post-chloramination treatment. In real waters, organic components showed more pronounced suppression on microcontaminant degradation efficiency than inorganic ions. This study provided a systematic investigation into the novel sunlight-induced monochloramine activation system for efficient microcontaminant degradation, and demonstrated the potential of the system in practical applications.

References for Small Fluorescence Quantum Yields.

Three compounds with fluorescence quantum yields in the range of 10- 5 to 10- 4 and emission spectra covering the UV/Vis spectral range are suggested as new references for the determination of small fluorescence quantum yields. The compounds are thymidine (dT) in water, dibenzoylmethane (DBM) in ethanol, and malachite green chloride (MG) in water, representing the blue, green, and red regions of the spectrum, respectively. All compounds are easily handled, photostable, and commercially available. Furthermore, these compounds exhibit a mirror-image symmetry between their absorption and fluorescence spectra. This symmetry, along with closely aligned fluorescence excitation and absorption spectra, confirms that the observed emissions originate from the compounds themselves. The fluorescence quantum yields were determined via a relative approach as well as Strickler-Berg analysis in conjunction with time resolved fluorescence spectroscopy. Within the respective error margins, the two approaches yielded identical results.

Direct Determination of Absolute Radical Quantum Yields in Hydroxyl and Sulfate Radical-Based Treatment Processes.

The absolute radical quantum yield () is a critical parameter to evaluate the efficiency of radical-based processes in engineered water treatment. However, measuring is fraught with challenges, as current quantification methods lack selectivity, specificity, and anti-interference capabilities, resulting in significant error propagation. Herein, we report a direct and reliable time-resolved technique to determine at pH 7.0 for commonly used radical precursors in advanced oxidation processes. For H2O2 and peroxydisulfate (PDS), the values of •OH and at 266 nm were measured to be 1.10 ± 0.01 and 1.46 ± 0.05, respectively. For peroxymonosulfate (PMS), we developed a new approach to determine with terephthalic acid as a trap-and-trigger probe in the nonsteady state system. For the first time, the value was measured to be 0.56 by the direct method, which is stoichiometrically equal to (0.57 ± 0.02). Additionally, radical formation mechanisms were elucidated by density functional theory (DFT) calculations. The theoretical results showed that the highest occupied molecular orbitals of the radical precursors are O-O antibonding orbitals, facilitating the destabilization of the peroxy bond for radical formation. Electronic structures of these precursors were compared, aiming to rationalize the tendency of the values we observed. Overall, this time-resolved technique with specific probes can be used as a reliable tool to determine , serving as a scientific basis for the accurate performance evaluation of diverse radical-based treatment processes.

Green synthesis of yeast cell wall-derived carbon quantum dots with multiple biological activities

HypothesisYeast cell walls are a sustainable biomass source containing carbon and other elements like phosphorus. Converting cell walls into valuable nanomaterials like carbon quantum dots (CQDs) is of interest. ExperimentsCell walls from Saccharomyces cerevisiae were hydrothermally treated in 0.5 M H2SO4 to produce CQDs. Multiple analytical techniques were utilized to confirm phosphorus-doping (P-CQDs), characterize the fluorescence properties, determine quantum yield, and evaluate the sensing, antimicrobial, photocatalytic, and antioxidant capacities. FindingsA successful synthesis of P-CQDs was achieved with strong blue fluorescence under UV excitation, 19 % quantum yield, and excellent stability. The P-CQDs showed sensitive fluorescence quenching in response to ferric ions with a 201 nM detection limit. Antibacterial effects against Escherichia coli and Staphylococcus aureus were demonstrated. P-CQDs also exhibited dye degradation under sunlight and antioxidant activity. So, the prepared P-CQDs displayed promising multifunctional capabilities for metal ion detection, disinfection, and environmental remediation. Further research is required to fully realize and implement the multifunctional potential of P-CQDs in real-world applications.

Mechanistic Investigation, Wavelength-Dependent Reactivity, and Expanded Reactivity of N-Aryl Azacycle Photomediated Ring Contractions.

Under mild blue-light irradiation, α-acylated saturated heterocycles undergo a photomediated one-atom ring contraction that extrudes a heteroatom from the cyclic core. However, for nitrogenous heterocycles, this powerful skeletal edit has been limited to substrates bearing electron-withdrawing substituents on nitrogen. Moreover, the mechanism and wavelength-dependent efficiency of this transformation have remained unclear. In this work, we increased the electron richness of nitrogen in saturated azacycles to improve light absorption and strengthen critical intramolecular hydrogen bonding while enabling the direct installation of the photoreactive handle. As a result, a broadly expanded substrate scope, including underexplored electron-rich substrates and previously unsuccessful heterocycles, has now been achieved. The significantly improved yields and diastereoselectivities have facilitated reaction rate, kinetic isotope effect (KIE), and quenching studies, in addition to the determination of quantum yields. Guided by these studies, we propose a revised ET/PT mechanism for the ring contraction, which is additionally corroborated by computational characterization of the lowest-energy excited states of α-acylated substrates through time-dependent DFT. The efficiency of the ring contraction at wavelengths longer than those strongly absorbed by the substrates was investigated through wavelength-dependent rate measurements, which revealed a red shift of the photochemical action plot relative to substrate absorbance. The elucidated mechanistic and photophysical details effectively rationalize empirical observations, including additive effects, that were previously poorly understood. Our findings not only demonstrate enhanced synthetic utility of the photomediated ring contraction and shed light on mechanistic details but may also offer valuable guidance for understanding wavelength-dependent reactivity for related photochemical systems.

Phenylbenzothiazole-Based Platinum(II) and Diplatinum(II) and (III) Complexes with Pyrazolate Groups: Optical Properties and Photocatalysis.

Based on 2-phenylbenzothiazole (pbt) and 2-(4-dimethylaminophenyl)benzothiazole (Me2N-pbt), mononuclear [Pt(pbt)(R'2-pzH)2]PF6 (R'2-pzH = pzH 1a, 3,5-Me2pzH 1b, 3,5-iPr2pzH 1c) and diplatinum (PtII-PtII) [Pt(pbt)(μ-R'2pz)]2 (R'2-pz = pz 2a, 3,5-Me2pz 2b, 3,5-iPr2pz 2c) and [Pt(Me2N-pbt)(μ-pz)]2 (3a) complexes have been prepared. In the presence of sunlight, 2a and 3a evolve, in CHCl3 solution, to form the PtIII-PtIII complexes [Pt(R-pbt)(μ-pz)Cl]2 (R = H 4a, NMe2 5a). Experimental and computational studies reveal the negligible influence of the pyrazole or pyrazolate ligands on the optical properties of 1a-c and 2a,b, which exhibit a typical 3IL/3MLCT emission, whereas in 2c the emission has some 3MMLCT contribution. 3a displays unusual dual, fluorescence (1ILCT or 1MLCT/1LC), and phosphorescence (3ILCT) emissions depending on the excitation wavelength. The phosphorescence is lost in aerated solutions due to sensitization of 3O2 and formation of 1O2, whose determined quantum yield is also wavelength dependent. The phosphorescence can be reversibly photoinduced (365 nm, ∼ 15 min) in oxygenated THF and DMSO solutions. In 4a and 5a, the lowest electronic transitions (S1-S3) have mixed characters (LMMCT/LXCT/L'XCT 4a and LMMCT/LXCT/ILCT 5a) and they are weakly emissive in rigid media. The 1O2 generation property of complex 3a is successfully used for the photooxidation of p-bromothioanisol showing its potential application toward photocatalysis.

Determining wavelength-dependent quantum yields of photodegradation: importance of experimental setup and reference values for actinometers.

Accurate quantum yields are crucial for modeling photochemical reactions in natural and engineered treatment systems. Quantum yields are usually determined using a single representative light source such as xenon lamps to mimic sunlight or UVC light for water treatment. However, photodegradation modeling can be improved by understanding the wavelength dependence of quantum yields and the potential errors introduced by the experimental setup. In this study, we investigated the effects of experimental setup on measured quantum yields using four photoreactor systems and up to 11 different light sources. When using a calibrated spectroradiometer to measure incident irradiance on an open solution surface, apparent quantum yields were up to two times higher if light reflection and light screening were not accounted for in the experimental setup. When the experimental setup was optimized to allow for accurate irradiance measurements, quantum yields were reproducible across photoreactors. The optimized experimental setup was then used to determine quantum yields of uridine, atrazine, p-nitroanisole (PNA), sulfamethoxazole, and diclofenac across the UV spectrum. No significant wavelength dependence of quantum yields was observed for sulfamethoxazole and diclofenac, in contrast to wavelength-dependent quantum yields for uridine, atrazine, and PNA. These reference values can be used for determining wavelength-dependent quantum yields of other compounds of interest. Additionally, more accurate results can be obtained when using (1) an actinometer with similar light absorption and photoreactivity compared to that of the target chemical, (2) optically transparent actinometer solutions that can account for light reflection within reaction vessels, and (3) a quantum yield that corresponds to the spectrum of the selected light source.

Fluorescence of p-hydroxyazobenzocrowns – Tautomeric equilibrium effect

The spectroscopic properties of a series of para-hydroxyazobenzocrowns, including three novel compounds, were investigated using UV–Vis absorption and emission spectroscopy. This study presents, for the first time, determined quantum yield (QY) values for macrocycles of this category, ranging between 0.122 and 0.195. The highest values were obtained for crowns bearing two phenyl substituents in benzene rings. The impact of aromatic ring substituents and macroring size on the spectral characterization (1H NMR and FTIR) of p-hydroxyazobenzocrowns was examined in consideration of the azophenol ⇄ quinone-hydrazone tautomeric equilibrium. Dipole moments of p-hydroxyazobenzocrowns in the ground and excited states have been determined. The alignment between experimental findings and theoretical studies was established.

Impact ionization in silicon at low charge-carrier energies

Photons absorbed in silicon produce electron–hole pairs, which can cause impact ionization and quantum yield larger than one. Reliable determination of quantum yield at low charge-carrier energies (<4 eV) has been challenging because photon losses due to reflectance and charge-carrier losses due to recombination affect the resulting photocurrent. Here, we present how the measurement of this fundamental characteristic of silicon crystals can be improved in the charge-carrier energy range of 1.6–4 eV by using a predictable quantum efficient detector based on induced junction photodiodes optimized for photon-to-electron conversion efficiency. The measured quantum yield values are compared with the results of theoretical calculations, revealing increased impact-ionization probabilities at 2.25 and 3.23 eV on the top of a smooth background curve calculated by a model based on free charge carriers in the silicon lattice. For the results at the lowest energies, both data and an asymptotic extrapolation model suggest that quantum yield exceeds unity by ∼10−4 at 1.6 eV corresponding to a photon wavelength of 450 nm.

Determination of excited triplet states of dissolved organic matter using chemical probes: A comparative and mechanistic study

Dissolved organic matter (DOM) plays an important role in the biogeochemical cycle in natural waters. The determination and characterization of the excited triplet state of DOM (3DOM*) have attracted much attention recently. However, the underlying differences of determined 3DOM* through different pathways are not yet fully understood. In this study, the differences and underlying mechanisms of the determined 3DOM* using 2,4-hexadien-1-ol (HDO) through an energy transfer pathway and 2,4,6-trimethylphenol (TMP) through an electron transfer pathway, were investigated. The results showed that the determined quantum yields of 3DOM* (Φ3DOM*) for four commercial and four isolated local DOMs are different using HDO ((0.04 ± 0.00) × 10−2 to (2.9 ± 0.17) × 10−2)) and TMP ((0.08 ± 0.01) × 10−2 to (1.2 ± 0.17) × 10−2), respectively. For 17 DOM-analogs, significant differences were also observed with the quantum yields of their 3DOM* determined using HDO (ΦHDO) and the triplet-state quantum yield coefficients determined using TMP (fTMP). It indicates the different reactivity of TMP and HDO with the excited triplet of the chromophores with different structures within the isolated DOM. Based on the experimental and predicted values of fTMP and ΦHDO for different DOM-analogs, the impact of substituents on differences in 3DOM* values were further revealed. These results demonstrated that the levels of 3DOM* depended on the chemical functionalities present in the DOM-analogs.

On the Quantum Yield Determination of UV Emitting Up-Converters.

This work deals with the determination of the external quantum yield of some selected inorganic up-conversion materials, which are able to convert blue light, as typically emitted using blue (In,Ga)N LEDs, into UV radiation. Recently, these materials have drawn tremendous attention due to their potential application in antimicrobial coatings of surfaces. To judge the viability of this approach to reduce the density of germs onto arbitrary surfaces upon indoor or outdoor illumination, the quantum efficiency for the conversion of blue light into UV is of large interest. We found that the quantum efficiency is between about 0.1% and 1%, which might be good enough if the illumination of the respective surface is performed for several hours. Then, a relevant reduction of the number of active microorganisms per area can be achieved.

Separation and online optical characterization of fluorescent components of pyrogenic carbons for carbon dots identification

Optical features of fluorescent components of pyrogenic carbons as flame-formed carbon particulate matter (PM) were studied by setting up a facile and fast method (SEC-Abs/Fluo) based on size exclusion chromatography (SEC) coupled with UV–Visible absorption and fluorescence spectrometers as detectors. The SEC-Abs/Fluo method simultaneously allowed the molecular weight (MW) separation and identification of blue- and green-fluorescent PM components exhibiting size and spectroscopic features typical of carbon dots (CDs). The SEC-Abs/Fluo method allowed the online determination of quantum yield (QY) and optical band gap of fluorescent components also in strongly-scattering carbon suspensions so avoiding tedious pretreatment of carbon samples. From the detailed separation and analysis of blue- and green-fluorescent PM components along with two commercial pitches, aromatic species having MW > 1000 u and band gap <1–1.5 eV resulted to be scarcely or no fluorescent indicating these are the MW and band gap thresholds for fluorescence emission. Indeed, a sharp QY decrease was for the first time noticed in a narrower band gap (1–1.5 eV) range, where carriers can more easily tunnel to defects of the carbon network reducing fluorescence emission. The exponential increase of QY as the band gap rises was found with a more regular trend for the MW-segregated components in comparison to the bulk samples. The method can support and guide the choice of the optimal operating conditions to maximize CD formation and their purification from not-fluorescing components and can also be helpful in disentangling CD fluorescence attribution.

Fluorescence Quantum Yield Standards for the UV/Visible/NIR: Development, Traceable Characterization, and Certification

The rational design of next generation molecular and nanoscale reporters and the comparison of different emitter classes require the determination of the fluorometric key performance parameter fluorescence quantum yield (Φf), i.e., the number of emitted photons per number of absorbed photons. Main prerequisites for reliable Φf measurements, which are for transparent luminophore solutions commonly done relative to a reference, i.e., a fluorescence quantum yield standard of known Φf, are reliable and validated instrument calibration procedures to consider wavelength-, polarization-, and time-dependent instrument specific signal contributions, and sufficiently well characterized fluorescence quantum yield standards. As the standard's Φf value directly contributes to the calculation of the sample's Φf, its accuracy presents one of the main sources of uncertainty of relative Φf measurements. To close this gap, we developed a first set of 12 fluorescence quantum yield standards, which absorb and emit in the wavelength region of 330-1000 nm and absolutely determined their Φf values with two independently calibrated integrating sphere setups. Criteria for standard selection and the configuration of these novel fluorescence reference materials are given, and the certification procedure is presented including homogeneity and stability studies and the calculation of complete uncertainty budgets for the certified Φf values. The ultimate goal is to provide the community of fluorescence users with available reference materials as a basis for an improved comparability and reliability of quantum yield data since the measurement of this spectroscopic key property is an essential part of the characterization of any new emitter.

Intermolecular Organophotocatalytic Cyclopropanation of Unactivated Olefins.

Intermolecular cyclopropanation of mono-, di-, and trisubstituted olefins with α-bromo-β-ketoesters and α-bromomalonates under organophotocatalysis is reported. The reaction displays broad functional group tolerance, including substrates bearing acids, alcohols, halides, ethers, ketones, nitriles, esters, amides, carbamates, silanes, stannanes, boronic esters, as well as arenes, and furnishes highly substituted cyclopropanes. The transformation may be performed in the presence of air and moisture with 0.5 mol% of a benzothiazinoquinoxaline as organophotocatalyst. Mechanistic investigations, involving Stern-Volmer quenching, quantum yield determination, and deuteration experiments, are carried out, and a catalytic cycle for the transformation is discussed.

Ultra-precise photothermal measurements reveal near unity photoluminescence quantum yields of molecular emitters in solution.

Molecules with a photoluminescence quantum yield (PLQY) approaching unity enable new applications such as efficient luminescent solar concentrators and spectral redistributors. Moreover, they have the potential for thermally assisted photon upconversion and optical refrigeration, for which the slightest amount of non-radiative loss is detrimental. However, when the PLQY is within a few percent of 100%, it cannot be precisely determined using standard techniques. Here, we combine spectroscopic measurements with photothermal techniques to determine the photothermal threshold energy, i.e. the minimum photon energy at which the chromophores produce heat upon excitation. The PLQY is directly related to this energy and is determined for six fluorescent molecules in low concentration solutions with an unprecedented precision down to ±0.003 within 95% confidence intervals. Independent measurements based on photothermal-deflection spectroscopy and thermal lensing spectroscopy generally provide values within the margin of error, demonstrating the reliability of this measurement concept. Solutions of perylene red in carbon tetrachloride are found to have the highest PLQY of the measured series, being 0.994 ± 0.003. In addition, we observe phonon-assisted, optical upconversion when exciting perylene red within its optical gap at photon energies below its photothermal threshold. Similar measurements on perylene orange in chloroform reveal the presence of low energy sub-gap impurities, preventing upconversion when exciting at the photothermal threshold.

POPTARTS: A New Method to Determine Quantum Yields in a Molecular Beam.

A new technique is reported to determine absolute photodissociation quantum yields, ϕdiss, in a molecular beam. The technique relies on a molecule having two available product channels, where a species in channel A can be converted photolytically to a species in channel B. The relative decrease in the species from channel A and the relative increase in species from B provide a direct measure of the relative product yield of each channel, with no external calibration required. In the event that only channels A and B exist, or at least dominate, then the sum rule ϕA + ϕB = 1 can be used to convert relative quantum yields into absolute yields. The technique is demonstrated using the well-understood and characterized photochemistry of HCHO. Formaldehyde photolysis at wavelengths near 310 nm produces either H + HCO (channel A) or H2 + CO (channel B). HCO can then be photolyzed with high efficiency into H + CO. The product state distributions for HCO from channel A, CO from channel B, and CO from the secondary HCO photolysis event are all well-known; this is not a requirement but is utilized here to demonstrate the veracity of the technique. The zero-pressure quantum yields of HCO from HCHO photolysis via the 2341 and 2151 states of HCHO are determined to be 0.66 and 0.74, respectively, which are in excellent agreement with the established quantum yields at atmospheric pressure and support the conclusion that HCHO quantum yields at these photolysis energies are not pressure dependent.

Air‐Stable Solid‐State Photoluminescence Standards for Quantitative Measurements Based on 4′‐Phenyl‐2,2′ : 6′,2′′‐Terpyridine Complexes with Trivalent Lanthanides

AbstractCorrect photoluminescence quantum yield (PLQY) determination in the solid state is vital for numerous application fields, such as photovoltaics, solid lighting or the development of phosphors. In order to increase the limited number of suitable standards for such determinations, two new Ln3+‐based complexes with 4′‐phenyl‐2,2′ : 6′,2“‐terpyridine γ‐[Ln4(OAc)12(ptpy)2] (1‐Eu with europium and 1‐Tb with terbium) are presented. The corresponding complexes show solid‐state QYs of 58(4) % and 46(3) %, respectively, exhibiting broadband absorption in the UV range from 380–200 nm. As Ln3+ ions in general exhibit narrow f‐f transitions, spectral regions with a broadness of 20–35 nm can be checked. Both complexes have suitable thermal stability, up to 270 °C, and are stable with respect to air and humidity, for 1‐Eu up to 75 % and for 1‐Tb up to 53 % relative humidity. These complexes are altogether suitable as standards to increase the reliability of PLQY determination and proposed to be used for a relative PLQY determination in the solid state.

Rhodamine-Tagged Polymethacrylate Dyes as Alternative Tools for Analysis of Plant Cells

A rhodamine B (RhB)-based initiator for atom transfer radical polymerization (ATRP) was synthesized and applied for preparation of poly(2-trimethylammoniumethyl methacrylate) (PChMA), poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(2-trimethylsilyloxyethyl methacrylate) (PHEMATMS). Polymer fluorescence was confirmed by determination of quantum yield by comparative method with piroxicam as the standard exhibiting dependency of emission intensity on the polymer chain hydrophilicity and the kind of solvent. The RhB functionalized polymers were used for biological tests in plant materials except for RhB-PHEMATMS because of weak fluorescence. These two polymers slightly differed in cellular localization. RhB-PChMA was mostly observed in cell walls of root tissues and cotyledon epidermis. It was also observed in cytoplasm and cell organelles of root cap cells and rhizodermis, in contrast with cytoplasm of cotyledon epidermis. RhB-PHEMA was also present in apoplast. A strong signal in protoxylem cell walls and a weak signal in cell walls of rhizodermis and cortex were visible. Moreover, it was also present in cell walls of cotyledon epidermis. However, RhB-PHEMA was mostly observed in cytoplasm and cell organelles of all root tissues and epidermis of cotyledons. Both RhB-polymers did not cause cell death which means that they can be used in living plant material.