Absorption and Fluorescence Properties of 3,6-bis(5-bromothiophen-2-yl)-2,5-bis(2-ethylhexyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione. A Covalent Fluorescence in Solution and in the Solid State

تم في هذا البحث دراسه الصفات الفيزياويه الضوئيه لمركب 3,6 – بس (5- برومو ثايوفينا-2-يل) – 2, 5- بس ( 2-ايثايل هكسايل) -2,5- داي هايدرو بايرولو (3,4-سي ) بايرول-1,4- دايون eh433f1. تظهر حزم الامتصاصيه في المنطقه المرئيه عند 527,558, و 362 نانوميتر في مذيب كاربونات البروبلين وأيضا يظهر المركب تفلور في المحلول وفي فلم البلاستيك بمدى 550-750 نانوميتر. ان قيم الستوك شفت  للمركب تساوي  734, 836, 668, 601, 601, 719, 804, سم-1 في مذيبات كاربونات البروبلين, الاسيتونايترايل, داي اثيل ايثر, تي اج اف , سايكوهكسان, داي بيوتايل ايثر, دي سي ام على التوالي. يظهر الفلم ازاحه حمراء حوالي 9 و 6 نانوميتر مقارنه مع الصبغه في مذيب الاستيونايترايل والذي يوصف نتيجه التداخلات الالكترونيه داخل الجزيئه. ان قيم الستوك شفت تكون قليله في مذيبات التي اج اف والسايكلوهكسان مقارنه مع باقي المذيبات والسبب يعود الى قله فقدان الطاقه في حالات التفلور والاثاره. شخصت الصفات الفيزياويه الضوئيه للمركب في المذيبات المختلفه اذ يظهر ازاحه حمراء قدرها 12 نانوميتر في مذيب التولوين مقارنه مع مذيب كاربونات البروبلين حيث ان قمه الطول الموجي 558 نانوميتر في مذيب كاربونات البروبلين. يظهر المركب ازاحه حمراء في قمه الامتصاصيه قدرها 5و 10 نانوميتر في مذيبات الداي اثيل ايثر والداي بيوتايل ايثر على التوالي. ان حزمه الامتصاص تكون غير حساسه الى قطبيه المذيب أي تظهر ازاحه حمراء في 563 نانوميتر في داي اثيل ايثر الى 569 نانوميتر في السايكلو هكسان أي  = 6 نانوميتر وايضا ازاحه حمراء في 558 نانوميتر في الاسيتونايترايل الى 570 نانوميتر في التلولوين  = 12 نانوميتر, حيث تعتمد الازاحه الحمراء على قطبيه المذيب. ان قمه حزمه الانبعاث للصبغه تظهر ازاحه حمراء في الدي سي ام والتولوين مقارنه مع المذيبات الاخرى. تظهر الصبغه ازاحه حمراء قدرها 5 نانوميتر بالانتقال من مذيب الاسيتونايترايل الى مذيب اقل قطبيه مثل داي كلورو ميثان الدي سي ام.In the cuurent article, the photophysical properties of 3,6-bis(5-bromothiophen-2-yl)-2,5-bis(2-ethylhexyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione were investigated. The visible absorption bands at 527, 558 and 362 nm in propylene carbonate and the compound was found to be fluorescent in solution and in the plastic film with emission wavelengths between 550- 750 nm. The Stokes Shift of P.C., acetonitrile, diethyl ether, Tetrahydrofuran THF, cyclohexane, dibutyl ether, and dichloromethane DCM  are 734, 836, 668, 601, 601, 719, and 804 cm-1 in respectively. The Stokes Shift Δ was less in THF and cyclohexane, than the solvents, which indicates that the energy loss is less between the excitation and fluorescence states. The photophysical characterizations were carried out on the compound in different solvents, the compound displays 12 nm red-shift in the absorption maximum in toluene compared with in propylene carbonate P.C, which the λmax was 558 nm in P.C. The compound displays 5 and 10 red-shifts in the absorption maximum in diethyl ether and dibutyl ether respectively. The absorption band is almost insensitive to the polarity of the solvent, showing only a slight red shift from 563 nm in diethyl ether to 569 nm in cyclohexane  and also red shift from 558 nm in acetonitrile to 570 nm in toluene , which appreciably red-shifted depending on the polarity of the solvent. The emission maxima of the dye slightly shift more red region, such as DCM and toluene when compared this compound in other solvents. The dye showed a slight red shift ca. 5 nm on moving from the acetonitrile to the less polar solvent, such as dichloromethane DCM

Methyl lactate synthesis using batch reactive distillation: Operational challenges and strategy for enhanced performance

YesBatch reactive distillation is well known for improved conversion and separation of desired reaction products. However, for a number of reactions, the distillation can separate the reactants depending on their boiling points of them and thus not only reduces the benefit of the reactive distillation but also offers operational challenges for keeping the reactants together. Methyl lactate (ML) synthesis via the esterification of lactic acid (LA) with methanol in a reactive distillation falls into this category and perhaps that is why this process has not been explored in the past. The boiling points of the reactants (LA, methanol) are about 490 K and 337 K while those of the products (ML, water) are 417 K and 373 K respectively. Clearly in a conventional reactive distillation (batch or continuous) methanol will be separated from the LA and will reduce the conversion of LA to ML significantly. Here, first the limitations of the use of conventional batch distillation column (CBD) for the synthesis of ML is investigated in detail and a semi-batch reactive distillation (SBD) configuration is studied in detail where LA is the limiting reactant and methanol is continuously fed in excess in the reboiler allowing the reactants to be together for a longer period. However, this poses an operational challenge that the column has to be carefully controlled to avoid overflow of the reboiler at any time of the operation. In this work, the performance of SBD for the synthesis of ML is evaluated using model based optimization in which operational constraints are embedded. The results clearly demonstrate the viability of the system for the synthesis of ML

Modelling and Optimization of Conventional and Unconventional Batch Reactive Distillation Processes. Investigation of Different Types Batch Reactive Distillation Columns for the Production of a Number of Esters such as Methyl Lactate, Methyl Decanoate, Ethyl Benzoate, and Benzyl Acetate using gPROMS

The synthesis of a number of alkyl esters such as methyl lactate, methyl decanoate, and ethyl benzoate via esterification in a reactive distillation is quite challenging. It is due to the complexity in the thermodynamic behaviour of the chemical species in the reaction mixture in addition to the difficulty of keeping the reactants together in the reaction section. One of the reactants (in these esterification reactions) having the lowest boiling point can separate from the other reactant as the distillation continues. This can result in a significant drop in the reaction conversion in a conventional reactive distillation whether it is a batch or a continuous column. To overcome this challenge, new different types of batch reactive distillation column configurations: (1) integrated conventional (2) semi-batch (3) integrated semi-batch (4) integrated dividing-wall batch distillation columns have been proposed here. Four esterification reaction schemes such as (a) esterification of lactic acid (b) esterification of decanoic acid (c) esterification of benzoic acid (d) esterification of acetic acid are investigated here. A detailed dynamic model based on mass, energy balances, chemical reaction, and rigorous thermodynamic (chemical and physical) properties is considered and incorporated in the optimisation framework within gPROMS (general PROcess Modelling System) software. It is found that for the methyl lactate system, the i-SBD operation outperforms the classical batch operations (CBD or SBD columns) to satisfy the product constraints. While, for the methyl decanoate system, the i-DWCBD operation outperforms all CBD, DWBD and sr-DWBD configurations by achieving the higher reaction conversion and the maximum product purity. For the ethyl benzoate system, the performance of i-CBD column is superior to the CBD process in terms of product quality, and conversion rate of acid. The CBD process is found to be a more attractive in terms of operating time saving, and annual profit improvement compared to the IBD, and MVD processes for the benzyl acetate system.The Higher Committee for Education Development in Iraq (HCED

A novel split-reflux policy in batch reactive distillation for the optimum synthesis of a number of methyl esters

YesThe production of a number of methyl esters such as methyl decanoate (MeDC), methyl salicylate (MeSC), and methyl benzoate (MeBZ) by esterification reactions of several carboxylic acids such as decanoic acid (DeC), salicylic acid (ScA), and benzoic acid (BeZ) with methanol, respectively, through a reactive distillation system (batch or continuous) is cost-intensive and operationally challenging operation. It is difficult to keep the reaction species together in the reaction section due to wide boiling point differences between the reactants. Methanol (in those esterification processes) having the lowest boiling temperature in the reaction mixture can separate easily from carboxylic acid as the distillation progresses, resulting in a severe drop in the reaction conversion ratio of the acid employing batch/continuous distillation system. In order to overcome this type of challenge and to increase the overall reaction conversion, a novel split-reflux conventional batch reactive distillation configuration (sr-BRD) is proposed/studied in detail in this investigation. The optimal performance of BRD/ sr-BRD column is determined in terms of maximum achievable conversion of acids, and highest concentration of the esters produced for each chemical reaction scheme. The results for given separation tasks are compared with those obtained using conventional batch distillation (BRD) process. The optimization results clearly show that the sr-BRD process significantly improves the process efficiency, the conversion ratio of acid, and the product purity of methyl esters compared to that obtained via the BRD process

Synthesis of methyl decanoate using different types of batch reactive distillation systems

YesMethyl Decanoate (MeDC) is a Fatty Acid Methyl Ester (FAME) and is an important chemical compound with global production of 31 million tons per year. However, synthesis of methyl decanoate (MeDC) via esterification of Decanoic Acid (DeC) with methanol by reactive distillation is operationally challenging due to difficulty of keeping the reactants together in the reaction zone as methanol being the lightest component in the mixture can separate itself easily form the other reactant deteriorating significantly the conversion of DeC using either conventional batch or continuous distillation column. This is probably the main reason for not applying the conventional route for MeDC synthesis. Whether Semi-batch Distillation column (SBD) and the recently developed Integrated Conventional Batch Distillation column (i-CBD) offer the possibility of revisiting such chemical reactions for the synthesis of MeDC is the focus of this paper. The minimum energy consumption (Qtot) as the performance measure is used to evaluate the performances of each of these reactive column configurations for different range of methyl decanoate purity and the amount of product. It is observed that the use of i-CBD column provides much better performance than SBD column in terms of the production time and the maximum energy savings when excess methanol is used in the feed. However, the SBD column is found to perform better than the i-CBD column when both reactants in the feed are in equal amount. Also, the optimization results for a given separation task show that the performance of two-reflux intervals strategy is superior to the single-reflux interval in terms of operating batch time, and energy usage rate in the SBD process at equimolar ratio

Environmental effects on the photophysics and photochemistry of some aromatic molecules

PhD ThesisAromatic molecules, especially polycyclic hydrocarbons, form a key cornerstone of molecular photophysics and have led to the identification of most of the main concepts, including excimer and exciplex formation. Derivatives of these compounds, most notably those including heteroatoms in the molecular framework, have expanded the field and provided many important applications. As such, the subject remains vibrant and progressive and there remains considerable interest in understanding the fundamental photophysical properties of aromatic molecules in solution and solid phases. In this thesis, we report the photophysical and photochemical properties of selected aromatic molecules with the intention of exposing the underlying environmental effects. The compounds have either been synthesized by specialist research groups or obtained from commercial sources. Chapter 1 presents a summary of the photophysical properties of aryl hydrocarbons and considers some of the better known examples of how selective substitution affects these properties. The chapter draws heavily on literature citations and seeks to introduce some of the subtleties of the field, focussing on fundamental aspects. The key objective is to enquire into how small structural changes influence the photophysics of these molecules and to consider the further effects caused by a change in environment. Basic theoretical considerations, such as the energy-gap law and the Strickler-Berg expression, are covered and the importance of spin-orbital coupling is highlighted. Chapter 2 is the first discussion chapter and deals with the structural dynamics and barrier crossing observed for a fluorescent O-doped polycyclic aromatic hydrocarbon. These materials are finding increasing applications in the emerging field of molecular-based organic electronics. It is shown that the oxygen atoms incorporated into the molecular backbone introduce unexpected flexibility such that the molecule functions as a fluorescent rotor. Temperature- and viscosity-dependence studies are used to calculate torsional barriers for the target molecule. Chapter 3 continues the discussion by way of considering the quest for highly fluorescent chromophores and introduces 1H,3H-isochromeno[6,5,4-mna]xanthene-1,3-dione. This compound, synthesized in-house, shows classical photophysical behaviour and has been studied in a range of organic solvents and at different temperatures. As a small molecule, with a relatively high dipole moment, this highly planar, rigid dye absorbs at around 420 nm, which is ideal for excitation with a blue laser diode, and is extremely stable towards prolonged illumination. Under near-UV excitation, the dye readily sensitises free-radical polymerisation, forming a plastic film with excellent optical v transparency. Weakly structured emission is observed with a small Stokes' shift and remains essentially insensitive to changes in solvent polarity. For example, in tetrahydrofuran the fluorescence quantum yield is 0.96 while the excited-singlet state lifetime is 7.4 ns. Quantum chemical calculations provide further insight into the electronic nature of the dye in solution. Chapter 4 represents a departure from the above approach and considers the fluorescence quantum yield of cresyl violet, a well-known emission standard for the red region. It is shown that this compound is highly susceptible to self-association in all solvents other than the smaller alcohols. The fluorescence quantum yield depends markedly on concentration, solvent polarity, temperature, etc. and we have attempted to quantify these various factors. The photophysical properties of cresyl violet are highly complicated and great caution should be exercised when using this compounds as a reference for fluorescence quantum yields. Chapter 5 describes exciton migration and surface trapping for a photonic crystal displaying charge-recombination fluorescence. The compound of interest is highly polar and the emission properties in solution depend markedly on the polarity of the surrounding solvent. Somewhat unusually, single crystals of this compound are reasonably fluorescent under near-UV illumination due to relatively slow charge recombination. The crystal can be doped with Rhodamine B, but the added dye adsorbs into a surface layer rather than interchelating into the bulk of the crystal. Excitation of the crystal leads to intense fluorescence from Rhodamine B even at astonishingly low dopant levels. Kinetic studies are used to formulate a mechanism for exciton migration and trapping. Chapter 6 describes the results collected for some water-soluble food dyes. The motivation for this work stems from a growing awareness of the need to avoid any kind of toxic compounds when developing practical applications. In fact, there are many dyes that have been used in the food industry for centuries and are believed to be essentially harmless. The cost and inconvenience inherent to testing new reagents for toxicity seems certain to cause renewed interest in these ancient dyes. Here, we explore the kinetics for photochemical bleaching of Phloxine B, Erythrosine, and Riboflavin in water. Some observations are raised regarding the relative stabilities and breakdown mechanisms. One of the systems studied here, namely the photolysis of Erythrosine, will form the basis of an undergraduate laboratory practical experiment. Chapter 7 summarises the experimental methods used throughout this work. Materials were obtained through other sources but all the spectroscopic studies were completed in-house. Fluorescence spectroscopy has been the main workhorse and we have amplified the work by examining the effects of the surrounding medium on the emission properties of the target compound. Temperature has been varied from 77K to over 200 0C using different experimental set-ups while special adapters have vi been designed for handling polymeric films or crystals. In all cases, the spectroscopic data were removed from the operating computer and analysed separately using homemade procedures. These are explained in the chapter.Higher Committee for Education Development in Iraq (HCED

Integrated Batch Reactive Distillation Column Configurations for Optimal Synthesis of Methyl Lactate

YesAlthough batch reactive distillation process outperforms traditional reactor-distillation processes due to simultaneous reaction and separation of products for many reaction systems, synthesis of Methyl lactate (ML) through esterification of lactic acid (LA) with methanol in such process is very challenging due to difficulty of keeping the reactants together when one of the reactants (in this case methanol) has the lowest boiling point than the reaction products. To overcome this challenge, two novel reactive distillation column configurations are proposed in this work and are investigated in detail. These are: (1) integrated conventional batch distillation column (i-CBD) with recycled methanol and (2) integrated semi-batch and conventional batch distillation columns (i-SBD) with methanol recovery and recycle. Performances of each of these configurations are evaluated in terms of profitability for a defined separation task. In i-SBD column, an additional constraint is included to avoid overflow of the reboiler due to continuous feeding of methanol into the reboiler as the reboiler is initially charged to its maximum capacity. This study clearly indicates that both integrated column configurations outperform the traditional column configurations (batch or semi-batch) in terms of batch time, energy consumption, conversion of LA to ML, and the achievable profit

Investigation about profitability improvement for synthesis of benzyl acetate in different types of batch distillation columns

YesIn this work, for the first time, the synthesis of benzyl acetate via the esterification of acetic acid and benzyl alcohol is investigated in the reactive distillation system using a middle vessel (MVD), inverted (IBD), and conventional batch reactive distillation columns. The measurement of the performance of these column schemes is determined in terms of profitability through minimization of the batch time for a defined separation task. The control variables (reboil ratio for MVD, IBD columns) and (reflux ratio in case of CBD column) are considered as piecewise constants over batch time. The optimization results obviously indicate that the CBD system is a more attractive process in terms of batch time reduction, and maximum achievable yearly profit as compared to the MVD, and IBD operations

Feasibility of Integrated Batch Reactive Distillation Columns for the Optimal Synthesis of Ethyl Benzoate

YesThe synthesis of ethyl benzoate (EtBZ) via esterification of benzoic acid (BeZ) with ethanol in a reactive distillation is challenging due to complex thermodynamic behaviour of the chemical reaction and the difficulty of keeping the reactants together in the reaction zone (ethanol having the lowest boiling point can separate from the BeZ as the distillation proceeds) causing a significant decrease in the conversion of BeZ in a conventional reactive distillation column (batch or continuous). This might be the reason of not reporting the use of reactive distillation for EtBZ synthesis although the study of BeZ esterification reaction is available in the public literature. Our recently developed Integrated Conventional Batch Distillation (i-CBD) column offers the prospect of revisiting such reactions for the synthesis of EtBZ, which is the focus of this work. Clearly, i-CBD column outperforms the Conventional Batch Distillation (CBD) column in terms of product amount, purity and conversion of BeZ and eliminates the requirement of excess use of ethanol. For example, compared with CBD column, the i-CBD operation can yield EtBZ at a much higher purity (0.925 compared to 0.730) and can convert more benzoic acid (93.57% as opposed to only 74.38%)

Feasibility of novel integrated dividing-wall batch reactive distillation processes for the synthesis of methyl decanoate

YesThe production of methyl decanoate (MeDC) through esterification of decanoic acid (DeC) with methanol by reactive distillation is operationally challenging and energy-intensive due to the complicated behaviour of the reaction system and the difficulty of retaining the reactants together in the reaction region. Methanol being the lightest component in the mixture can separate itself from the reactant DeC as the distillation proceeds which will cause a massive reduction in the conversion of DeC utilizing either a batch or continuous distillation process. Aiming to overcome this type of the potential problem, novel integrated divided-wall batch reactive distillation configuration (i-DWBD) with recycling from the distillate tank is established in this study and is examined in detail. This study has clearly demonstrated that the integrated divided-wall batch reactive distillation column (i-DWBD) is superior to the traditional conventional batch distillation (CBD) and both the divided-wall (DWBD), and split reflux divided-wall (sr-DWBD) batch reactive distillation configurations in terms of maximum achievable purity of MeDC and higher conversion of DeC into MeDC. In addition, significant batch time and energy savings are possible when the i-DWBD is operated in multi-reflux mode