Pure Reactants Research Articles

Application of MIL-101(Cr) for biofuel dehydration and process optimization using the central composite design method.

Nowadays, researchers from various fields are aiming to replace petro-based and other fossil fuels with green and renewable alternatives. One of the potential candidates, requiring a highly pure reactant, is biofuel. The use of alcohol-containing water as a reactant can lead to different types of problems including the generation of side reactions, hydrolysis, equilibrium shifts, catalyst deactivation and process complexity. A metal-organic framework, MIL-101(Cr), was successfully synthesized using the hydrothermal method and subsequently employed for the dehydration of a standard biofuel. With this goal in mind, we aimed to optimize the effects of operational parameters-specifically, initial water concentration, adsorbent dosage, and temperature-using the central composite design (CCD) method, while also analyzing their behaviors by applying variance analysis. To predict the process behavior, we propose a refined quadratic equation under various conditions, achieving an R 2 value of 95.26. The results showed that the process was more influenced by temperature variations than the other two parameters. The optimal conditions were predicted with an initial concentration of 1.41, catalyst dosage of 0.14, and a temperature of 302.5 K, resulting in a capacity of 1349.72 and a desirability value of 0.95. Additionally, the synthesized MIL-101(Cr) was characterized using XRD, SEM, DSC/TGA, and N2 physisorption techniques. The results indicated that the particles possessed microporous windows and mesoporous cages, exhibiting a uniform octahedral shape with an average size ranging between 200 and 500 nm.

A Physical Basis for Kinetic Compensation.

Kinetic compensation is a strong, positive correlation between the Arrhenius activation energy E and the frequency factor A for a reaction between the same reactants under similar experimental conditions or similar reactants under the same conditions, even though these parameters are supposed to be independent. The kinetic compensation effect (KCE) is demonstrated by a linear relationship between ln[A] and E/R in the eponymous Constable plot and has been the subject of more than 50 000 publications over the past 100 years, with no consensus opinion about the cause of this effect. In this paper, it is suggested that the linear relationship between ln[A] and E is the result of a real or spurious path dependence of the reaction history between the initial state of the pure reactant(s) and the final state of the pure product(s) having standard enthalpy and entropy differences, ΔH° and ΔS°, respectively. The single-step rate law approximation of a reversible reaction leads to T0 = H°/ΔS° as the dynamic thermal (thermodynamic) equilibrium temperature and 1/T0 = (ln[A̅/k0])/(E̅/R) as the slope of a Constable/KCE plot or the crossover temperature of Arrhenius lines in an isokinetic relationship (IKR), where A̅ and E̅ are mean values for the ensemble of compensating {Ei, Ai} pairs and k0 is a constant that accounts for the path dependence of the reaction history and reconciles the KCE with the IKR. This proposed physical basis for the KCE and IKR is supported by qualitative agreement between ΔH° and ΔS° calculated from the statistics of compensating {Ei, Ai} pairs in the literature, and the difference in the standard enthalpies and entropies of formation of the products and reactants for thermal decomposition of organic peroxides, calcium carbonate, and poly(methyl methacrylate).

Hydration behavior of an experimental tricalcium silicate/tetracalcium phosphate bio-cement in Streptococcus thermophiles bacterial solution in comparison with distilled water used as a root canal furcation perforation repair material

BackgroundThe aim of this study is to evaluate an experimental tricalcium silicate phase (C3S) and tetracalcium phosphate (TTCP) material to be used as a root canal furcation perforation repair. C3S and TTCP phases were synthesized in nano-size particles by firing the required molar ratios of chemically pure reactants by solid-state reactions at elevated temperatures. The influence of Streptococcus thermophilus bacterial medium on the hydration reaction characteristics and morphology of 1:1 composite material of C3S and TTCP in comparison with distilled water was studied. Setting time, micro-hardness, pH of immersion solution, calcium ion concentration, phosphorous ion concentration, XRD, FTIR, scanning electron microscopy and cytotoxicity of the synthesized composite were investigated, and also, its sealing ability in bacterial media and in distilled water was evaluated.ResultsThe results showed that curing of pastes in the bacterial medium did not inhibit the hydration process of the synthesized composite but surface softening due to the great acceleration and encapsulation effects of the highly ionized curing medium resulting in lower micro-hardness values. The dissolution of TTCP phase was also increased in the bacterial medium resulting in precipitation of more hydroxyapatite inside the more porous system of pastes cured in the bacterial solution which was also evident by a non-significant decrease in the sealing ability in bacterial medium.ConclusionsMixing of tricalcium silicate (C3S) and tetracalcium phosphate (TTCP) resulted in a mix that was stable in bacterial medium and could be used for root canal perforation repair.

Hydration behavior and formation of strätlingite compound (C2ASH8) in a bio-cement based on tri-calcium silicate and mono-calcium aluminate for dental applications: influence of curing medium

BackgroundThe aim of this work was to study the influence of simulated body fluid (SBF) and Pseudomonas aeruginosa (in Mueller Hinton Broth, MHB media) on the hydration reactions, formation of strätlingite (C2ASH8) and morphology of a composite material based on nano-size tri-calcium silicate (C3S) and tri-calcium aluminate (CA) phases. The two experimental phases were prepared in laboratory by firing the required molar ratios of chemically pure reactants by solid-state reactions at elevated temperatures. Investigation of setting time, micro-hardness, pH of immersion solution, X-ray diffraction analysis, infrared spectroscopy, scanning electron microscopy and cytotoxicity were also carried out.ResultsThe results emphasized that the hydrated compounds of C3S phase can partly solve the problem of conversion process through the formation of the more stable and highly mechanical stratlingite hydrate (C2ASH8) plates that results in an increase in hardness values for samples cured in distilled water (DW) at 37 °C. The SBF solution showed more strength loss than those cured in Pseudomonas aeruginosa microbe (MHB) medium bacterial solution. SEM and EDAX analyses emphasized the formation of hydroxyapatite at 37 °C.ConclusionsThe prepared cements are promising for dental application.

Reduced Combustion Mechanism for Fire with Light Alcohols

The need for sustainable energy has incentivized the use of alternative fuels such as light alcohols. In this work, reduced chemistry mechanisms for the prediction of fires (pool fire, tank fire, and flash fire) for two primary alcohols—methanol and ethanol—were developed, aiming to integrate the detailed kinetic model into the computational fluid dynamics (CFD) model. The model accommodates either the pure reactants and products or other intermediates, including soot precursors (C2H2, C2H4, and C3H3), which were identified via sensitivity and reaction path analyses. The developed reduced mechanism was adopted to predict the burning behavior in a 3D domain and for the estimation of the product distribution. The agreement between the experimental data from the literature and estimations resulting from the analysis performed in this work demonstrates the successful application of this method for the integration of kinetic mechanisms and CFD models, opening to an accurate evaluation of safety scenarios and allowing for the proper design of storage and transportation systems involving light alcohols.

Process modelling for the production of hydrogen-rich gas from gasification of coal using oxygen, CO2 and steam reactants

This process modelling studied the effect of different reactants on syngas composition and gasifier heat duty (heat energy required to carry out the operation) and the downstream treatment of CO rich syngas to maximise hydrogen yield. The process modelling was validated against experimental data obtained from a large bench-scale entrained flow gasifier. Results show that considering the H2/CO ratio, the steam-O2 reactant favours the most compared to those of the pure oxygen and oxygen-CO2 reactants. Under comparable operating conditions, the highest H2/CO ratio of 0.74 was determined using steam-O2 reactant compared to that of 0.31 and 0.33 using steam-CO2 and pure oxygen reactant. The catalytic water-gas shift reaction (WGSR) favours the yield of H2 with complete CO conversion at a temperature of 400 °C using the steam/coal ratio of 1.2. Supplying steam in the gasifier requires more heat energy to be supplied to drive endothermic gasification reaction and maintain the gasifier temperature. Under complete carbon conversion, steam-CO2 and steam-oxygen reactants require 5–65 kW more energy than pure oxygen.

Chitosan/Xanthan Gum Based Hydrogels as Potential Carrier for an Antiviral Drug: Fabrication, Characterization, and Safety Evaluation.

This study investigated the use of pure polymer chitosan (CS), xanthan gum (XG), monomer 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and initiator potassium persulfate (KPS) as drug carrier system crosslinked through N′ N′-methylene bis-acrylamide (MBA) for controlled drug delivery of acyclovir (ACV). ACV is highly effective and selective antiviral drugs used for prophylaxis and treatment against herpes simplex viruses (HSV) infections. Present oral marketed formulations are associated with number of side effects and shortcomings which hampered its clinical effectiveness. Hydrogels (FCX1-FCX9) composed of CS, XG, AMPS, MBA, and KPS were prepared by free radical polymerization technique and characterized through FTIR, PXRD, thermal analysis and SEM. Swelling dynamics and drug release behavior was also investigated. FTIR studies confirmed that ACV was successfully encapsulated into hydrogel polymeric network. SEM revealed porous structure whereas thermal analysis showed enhanced thermal stability of polymeric network. PXRD indicated amorphous dispersion of ACV during preparation process. Swelling dynamics and ACV release behavior from developed hydrogels was dependent on pH of the medium and concentration of pure reactants used. Korsmeyer-Peppas model was best fit to regression coefficient. The present work demonstrated a potential for developing a pH sensitive hydrogel for an antiviral drug ACV by using pure polymers CS, XG, and monomer AMPS.

Simulation and Optimization of Isopropyl Lactate Manufacturing Process

The new chemical processes are investigated in laboratory, usually in batch, with pure reactants, and specific laboratory methods applied for the purification of the products. Scaling-up processes means passing from batch to continuous process, using feed with impurificators, industrial equipment for separation and recirculation or purge for an economic operation with special care for safety and environment. This is why, following a study in laboratory for isopropyl lactate obtaining by transesterification in reactive distillation system, a flowsheet of the industrial process was proposed in this paper. Simulations of the transesterification process were performed. The purpose of these simulations has been to find the optimum solution from energy consumption point of view. Optimum parameters of the reactive distillation were found: the molar ratio isopropanol/methyl lactate R= 1.06, the number of theoretical stages in the distillation zone NTS=2.4 and the reflux ratio RR=2, in a process that produces 1.3 t/h IPL of 96% wt purity.

Electrochemical Ammonia Synthesis Using a BZCYYb4411 Proton Conductor

The Haber Bosch process is the dominant route to synthesizing ammonia. Ammonia is an important component in fertilizers, which are widely used across the agriculture community. Dependence on the Haber Bosch process is detrimental because: (1) this process operates at high temperatures (~450°C)1 and pressures (150-300 bar) and accounts for 2% of the worlds energy supply2, (2) contributes 1% of all CO2 emissions, and (3) is typically centralized which limits access in developing worlds. Electrochemical ammonia production has the potential to greatly reduce society’s carbon footprint and energy consumption, as well as increase ammonia production in developing worlds and rural communities. This type of ammonia synthesis method has been shown to operate with air and water sources as opposed to highly pure nitrogen and hydrogen reactants used in commercial plants. Solid state electrochemical systems are able to operate at elevated temperatures (300-600 °C) unlike ambient processes (low temperature fuel cells) and thus have the potential for higher yields. Solid state ceramic proton conductors show high ionic conductivities (1E-2 Scm-1 at 600°C)3 and are stable in this intermediate temperature range. Currently, the investigation of intermediate temperature ion conductors in solid state ammonia synthesis is nascent but growing in interest. Herein, we describe the synthesis and processing of a highly conductive proton conductor BaZr0.4Ce0.4Y0.1Yb0.1O3- δ (BZCYYb4411) (Fig. 1a,b) is characterized and implemented in a solid state fuel cell arrangement. BZCYYb4411 is synthesized using a solid-state reaction route and Ag-Pd catalyst is used to make a symmetric cell. In this one chamber reactor employing 3% H2/N2, the faradaic efficiency and ammonia production rate is explored at different temperatures and operating voltages to elucidate the optimal conditions for ammonia synthesis. (1) Kyriakou, V.; Skodra, A.; Stoukides, M.; Vasileiou, E.; Garagounis, I. Electrochemical Synthesis of Ammonia in Solid Electrolyte Cells. Front. Energy Res. 2014, 2 (January), 1–10. (2) Martín, A. J.; Shinagawa, T.; Pérez-Ramírez, J. Electrocatalytic Reduction of Nitrogen: From Haber-Bosch to Ammonia Artificial Leaf. Chem 2019, 5 (2), 263–283. (3) Choi, S.; Kucharczyk, C. J.; Liang, Y.; Zhang, X.; Takeuchi, I.; Ji, H. Il; Haile, S. M. Exceptional Power Density and Stability at Intermediate Temperatures in Protonic Ceramic Fuel Cells. Nat. Energy 2018, 3 (3), 202–210. Figure 1

Controlling luminescence and quenching mechanisms in subnanometer multilayer structure of europium titanium oxide thin films

We have investigated how layered structures of TiO2 and Eu2O3 on the subnanometer scale control the optical absorption, energy transfer, emission and quenching mechanisms in sensitized lanthanide luminescence systems. By using atomic layer deposition (ALD) as a tool for designing materials with sub nanometer precision, we have been able to make structures ranging from separate (TiO6)8- clusters to bulk TiO2, and series of samples showing transitions from 3D to 2D energy migration. Photoluminescence, excitation and decay measurements have been used alongside transmission electron microscopy (TEM) to investigate how the different structures affect the luminescence. We show that it is possible to drastically suppress concentration quenching compared to solid solutions by designing materials as multilayered structures that confines energy migration in 2D planes. This allows for application of higher concentrations of lanthanides and more defected structures, also enabling use of less pure reactants during synthesis.

Approximating Catalyst Effectiveness Factors with Reaction Rate Profiles

A novel approximate solution for catalyst effectiveness factors is presented. It is based on carefully selected approximate reaction rate profiles, instead of typical assumption of composition profiles inside the catalyst. This formulation allows analytical solution of the approximate model, leading to a very simple iterative solution for effectiveness factor for general nonlinear reaction stoichiometry and arbitrary catalyst particle shape. The same model can be used with all practical Thiele modulus values, including multicomponent systems with inert compounds. Furthermore, the correct formulation of the underlying physical model equation is discussed. It is shown that an incorrect but often-used model formulation where convective mass transfer has been neglected may lead to much higher errors than the present approximation. Even with a correctly formulated physical model, rigorous discretization of the catalyst particle volume may have unexpectedly high numerical errors, even exceeding those with the present approximate solution. The proposed approximate solution was tested with a number of examples. The first was an equimolar reaction with first order kinetics, for which analytical solutions are available for the standard catalyst particle geometries (slab, long cylinder, and sphere). Then, the method was tested with a second order reaction in three cases: 1) with one pure reactant, 2) with inert present, and 3) with two reactants and non-stoichiometric surface concentrations. Finally, the method was tested with an industrially relevant catalytic toluene hydrogenation including Maxwell-Stefan formulation for the diffusion fluxes. In all the tested systems, the results were practically identical when compared to the analytical solutions or rigorous finite volume solution of the same problem.

Catalytic microreactor with electrodeposited hierarchically nanostructured nickel coatings for gas-phase fluorination reactions

The fabrication of a catalytic microreactor for the reaction of undiluted carbonyl difluoride and elemental fluorine to synthesize trifluoromethyl hypofluorite, CF3OF, on CsF catalyst supported on F2-passivated nanosctructured Ni coating was studied. The nanosctructured Ni support for catalyst immobilization was electrodeposited by a two-step procedure, consisting of a low current density step followed by a brief high current density one, for a hierarchical differentiation of structural features. An aqueous solution of NiCl2 with diethanolamine, as crystal modifier, and sodium lauryl sulphate, as anti-pitting agent, was used as electrolyte. Constant-pH Ni electrocrystallization was performed on H2SO4-etched Cu substrates in a range of pH from 1 to 4 via a HCl/H3BO3 based buffer. Passivation was carried out under up to 300mbar of undiluted F2. XRD, XPS, SEM, AFM, and static contact angle measurements were performed. Ni coatings obtained from pH 3 electrolytes were selected for microreactor fabrication on the basis of characterization data, due to the reproducibility and homogeneity of the structured Ni layers. The catalytic microreactor allowed the quantitative production of CF3OF from pure reactants, on demand, and removing any criticality relative to thermal and safety control of the synthesis. The CF3O-group selective transfer ability of the synthetized hypofluorite has raised interest in pharmaceutical and agrochemical industries in recent years.

Modified-screen printed electrode in flow system for measuring the electroactivity of nanoparticles towards alcohol electrooxidation

New multimetallic catalysts immobilized on different carbon supports have been developed to be used as anodes in direct alcohol fuel cells (DAFC). The performance of a new catalyst is evaluated by classic electrochemical measurements, which are performed in extremely clean systems, in an inert atmosphere, using pure reactants and usually in a stationary configuration. However, real DAFCs might operate in the presence of impurities, in O2-containing fuel and under hydrodynamic conditions, where the fuel continuously feeds the anode. Here, we propose a new flow system for measuring the electroactivity of nanoparticles (FSMEN). We take advantage of a flow injection system integrated with a screen-printed electrode cell to develop our method. In FSMEN, the fuel solution is continuously carried directly to the screen-printed electrode modified with candidate nanoparticles (NPs) to be used as anode of DAFC. During the injection, anodic current is generated when the fuel reaches the surface of the catalysts under a potential suitable for the electrooxidation reaction. We used FSMEN to investigate the activity of Pt NPs immobilized on carbon, multi-walled carbon nanotubes and graphene nanoribbons towards methanol electrooxidation, in comparison to classic measurements. Our method is robust, reproducible and provides new information due to the hydrodynamic current output and the use of an opened system, which is closer to a real fuel cell scenario.

Monitoring Photochemical Reactions in Single Crystals by X-ray Diffraction: Practical Aspects

The influence of external stimuli on the decrease of crystal diffracting power and hence the quality of diffraction patterns and determined structures was studied in the case of the Norrish-Yang photochemical reaction of methyl 2-{[4-(2,4,6-triisopropylbenzoyl)benzoyl]amino}-3-phenylpropanoate, compound 1. The reaction was conducted in a single-crystal-to-single-crystal homogeneous manner. The calculated rate constant at 75 °C was 1.6 × 10−3 s−1. In a quantitative way we illustrated a relationship between the reduction of the crystal diffracting power and the content of reactant molecules in the crystal and quantitatively showed that reactant molecules are responsible for this reduction. We observed that there is no correlation between the energy of UV–vis radiation applied to induce the photochemical reaction and the degree of the decrease of crystal diffracting power. We also showed in the case of the studied crystals that some change in temperature does not influence the degree of the decrease of the crystal diffracting power under the influence of UV–vis radiation. The unknown structures of the crystals containing pure reactant and product for compound 1 were also presented. The influence of different external stimuli on the reduction of diffracting power of crystals was monitored quantitatively during and after the Norrish-Yang photochemical reaction.

Influence of Structural Effects on Platinum Electrodes in the Preferential Adsorption of CO and Methanol in Acid Media

The complete methanol electro-oxidation on platinum single crystal electrodes produces CO2, H2O and 6 e- in acidic medium. However methanol adsorption is sensitive to the platinum surface orientation, showing different reactivity for different platinum crystallographic planes. In this work, it was studied the preferential adsorption and oxidation of carbon monoxide (CO) and methanol in acid media on polycrystalline and low index planes of platinum single crystals. In the experimental procedure carbon monoxide was bubbled in methanol solution with the platinum electrode polarized at 0.1 V vs. RHE. Then, the potential was scanned from 0.1 to 0.8 or 1.0 V vs ERH depending on platinum single crystal electrode. From Figure 1a the carbon monoxide oxidation occurs at potential above 0.6 V vs. RHE for all platinum surfaces. Besides data from Figure 1b methanol oxidation on Pt(111), Pt(100) and polycrystalline platinum electrodes exhibited high potential, above 0.8 V (RHE). After adsorption of carbon monoxide on platinum electrodes, on polycrystalline platinum and Pt(100) the peak maximum occurred at more positive potential compared with methanol reaction. In this case methanol oxidation only was promoted after carbon monoxide oxidation reaction. On Pt(100) and Pt(111) the adsorption of CO contributed to reduce the potential for methanol oxidation. Thus, these experiments suggest that carbon monoxide competes with methanol for adsorption on platinum electrode. For polycrystalline Pt and Pt(110) single crystals, the mixture CO+CH3OH showed potential of oxidation larger than with pure reactants. On the other hand, on Pt (111) and Pt(100) the oxidation of methanol happens at potential above that for the mixture of methanol and carbon monoxide, so that, it is possible that the electrochemical reaction follows different pathways on these surfaces. Figure 1. (a) first potential scan at platinum electrodes in 0.2 M CH3OH + 0.1M H2SO4, obtained at 10 mV s-1. Insert show CO peak between 0.2 – 0.4 V (RHE). (b) Potential peak maximum dependence for CO, CH3OH and CO + CH3OH oxidation. Acknowledgedment:CNPq for financial support (process 150885/2012-1).

Modeling Chemical Incompatibility: Ammonium Nitrate and Sodium Salt of Dichloroisocyanuric Acid as a Case Study

The dramatic accident involving ammonium nitrate (AN) that took place at Toulouse in September 2001 has once again focused attention on the hazards pertaining to chemical incompatibility in an industrial environment. To complete the experimental results, a detailed theoretical study was performed to better understand the involved mechanisms, considering the reaction between ammonium nitrate and the sodium salt of dichloroisocyanuric acid (SDIC). Starting from theoretical results obtained for the pure reactants, the gas-phase decomposition mechanism of the mixture was investigated and fully characterized by means of density functional theory (DFT) calculations. Beyond the complete characterization, in terms of intermediate structures and energies, of the decomposition pathways, the results evidenced the role of water in catalyzing the decomposition reaction, through a significant decrease of the activation energy of the rate-determining step. These results, in qualitative agreement with the calorimetric ex...

Structural changes induced in crystals by the photocyclization and high pressure

Photo-induced processes in crystals studied by means of X-ray structure analysis are the main subject of our interest. In particular, we monitor structural changes brought about by photochemical reactions. Nowadays, we have started to study influence of high pressure on them. In this poster, the results on monitoring structural changes in crystals of 2-tert-butylphenylphenylmethanone proceeding during the photocyclization reaction at ambient and high pressure will be presented. The studies demanded determination of structures of the pure reactant, pure product and many partly reacted crystals (Fig. 1) and were carried out at 0.1 MPa and 0.55, 1.27 and 1.50 GPa. Variations in the cell constants, geometry of the reaction centre and behavior of molecules during the phototransformation at various pressures will be presented. Several differences and similarities were observed. The studies provided knowledge on the path of the reaction in crystals and the influence of external factors, i.e. pressure, on it. Acknowledgments: The work was carried out within the grant 2011/01/D/ST5/02834 financed by the National Science Centre (Poland) and the fellowship co-financed by European Union within European Social Fund (Wroclaw University of Technology, Poland).

Energy and exergy analysis of the silicon production process

We used energy and exergy analysis to evaluate two industrial and one ideal (theoretical) production process for silicon. The industrial processes were considered in the absence and presence of power production from waste heat in the off-gas. The theoretical process, with pure reactants and no side-reactions, was used to provide a more realistic upper limit of performance for the others. The energy analysis documented the large thermal energy source in the off-gas system, while the exergy analysis documented the potential for efficiency improvement. We found an exergetic efficiency equal to 0.33 ± 0.02 for the process without power production. The value increased to 0.41 ± 0.03 when waste heat was utilized. For the ideal process, we found an exergetic efficiency of 0.51. Utilization of thermal exergy in an off-gas of 800 °C increased this exergetic efficiency to 0.71. Exergy destructed due to combustion of by-product gases and exergy lost with the furnace off-gas were the largest contributors to the thermodynamic inefficiency of all processes.

Grafting of styrene onto polyethylene in near critical media

AbstractIn this work, near critical n‐heptane is used as reaction medium for the copolymerization of polyethylene with styrene monomer, using alkylation reaction with different amounts of aluminum chloride (AlCl3) as catalyst. In this way, polyethylene chains will be more available to react with the catalyst. The reaction effect on pure reactants, as well as, the catalyst activity was previously investigated. The reaction occurrence was corroborated by analyzing the reaction products before and after careful polystyrene extraction with tetrahydrofuran. The reaction products were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy, transmission electron microscopy, differential scanning calorimetry, and size exclusion chromatography. The possible architecture for the copolymer molecule was proposed from the molecular characterization results. On the other hand, the polystyrene grafting modifies final properties of polyethylene, increasing the oxygen barrier properties without deteriorating significantly the mechanical properties of the films. In this sense this reaction seems to be a promising route to modify PE films to increase the barrier properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Kinetics of reversible photoisomerization: determination of the primary quantum yields for the E-Z photoisomerization of silylenephenylenevinylene derivatives

The kinetics scheme for directly excited, photoreversible reactions is solved exactly under the assumptions of no irreversible side reactions and constant excitation intensity for the duration of the reaction. The advantages of the methodology over the extrapolation-to-zero-time and the back-reaction correction methods are (i) that the quantum yields of both the forward and reverse photoreactions can be obtained starting from either pure reactant or pure product and (ii) the conversion percentage is not limited to a narrow domain in the neighborhood of small conversions. Examples of E-Z photoisomerizations are given to illustrate the fitting procedures required. The results from these examples are compared to the photoisomerization method of extrapolating the empirical quantum yields to zero time and the back-reaction correction. The exact equations are used to justify the extrapolation-to-zero-time method and to establish criteria on extrapolation ranges for the conversion percentage of starting material.