Academic literature on the topic 'Stern-Volmer'

The fluorescence quenching of coumarin derivative, 6-methoxy-4-p-tolyloxymethyl-chromen-2-one by aniline is carried out in different solvent mixtures of benzene and acetonitrile at room temperature. The quenching is found to be appreciable and a positive deviation from linearity is observed in the Stern–Volmer plot in all the solvent mixtures. Various rate constants for fluorescence quenching processes have been estimated using a sphere of action static quenching model and a finite sink approximation model. From the positive deviation of linear Stern–Volmer plots and dependence of rate constants on the polarity of the solvents, it has been inferred that the quenching process is diffusion-limited, and static as well as dynamic quenching processes are responsible for the observed positive deviation in the Stern–Volmer plot. Further, both models have been found to agree well with transient state also in pure acetonitrile and benzene solvents.

The fluorescence quenching of the dye Safranine T by various inorganic anions such as [Fe(CN6)]–3, [Fe(CN6)]–4, I–, Br–, NO2–, and N3– in aqueous solution and in nonionic micellar solutions of Tweens (Tween 20, Tween 40, and Tween 80) was studied. The Stern–Volmer quenching constants and quenching rate constants were evaluated. Compared to the quenching efficiency in aqueous media, that of the micellar media was found to be lower, except when iodide ion was used as a quencher. With the exception of the iodide ion, it has been established that collisional quenching plays a major role in the photophysical process. In the case of the iodide ion, both static and collisional quenching processes play a major role, owing to the complexation of iodide ion with Tween micelles. The Stern–Volmer quenching constants were found to be dependent on the ionic strength of the medium.Key words: fluorescence, static quenching, Tweens, Stern–Volmer constant, micellar media.

Stern-Volmer plots are simulated for the case of static quenching due to 1:1 ground-state complexation of quencher and fluorophore in solution, and compared with previously obtained experimental data. For cases where the association constant KC > 105 dm3 mol-1, upward curvatures of Stern- Volmer plots are expected. When KC is between 103 and 105 dm3 mol-1 linearity is obtained, while for KC < 103 dm3 mol-1 upward curvatures are again predicted. The significance of these results to fluorescence quenching experiments in general is discussed.

Fluorescence quenching of 2-(4'-t-Butylphenyl)-5-(4"-biphenylyl)-1,3,4-oxadiazole (BPBD) by aniline in toluene has been carried out at room temperature by steady state and time resolved fluorescence spectroscopy. The Stern-Volmer plot by steady state method has been found to be non-linear showing a positive deviation, whereas by time-resolved method it is linear. In order to interpret these results we have used the ground state complex and sphere of action static quenching models. Using these models various rate parameters have been determined. Based on these models, with finite sink approximation model, we conclude that positive deviation Stern-Volmer plot is due to the simultaneous presence of dynamic and static quenching processes.

The photophysical and photochemical properties and quenching (by 1,4-benzoquinone) of metallophthalocyanine sulfonates of aluminium ( AlPcSmix), zinc ( ZnPcSmix), silicon ( SiPcSmix), germanium ( GePcSmix) and tin ( SnPcSmix) are presented. The quantum yield values of fluorescence (ΦF), triplet state (ΦT), singlet oxygen (ΦΔ) and photodegradation (Φd) were determined and the observed trends in their variation among the complexes discussed in terms of aggregation and the heavy atom effect. 1,4-benzoquinone effectively quenched the fluorescence of the complexes. Quenching analyses gave positive deviations from Stern-Volmer behavior, suggesting the existence of static quenching in addition to dynamic quenching. The static and dynamic components of the quenching were separated using a modified Stern-Volmer equation and the “sphere of action quenching model”. The quenching constant was found to be a function of the radius of the central metal ion.

This paper presents a study of the fluorescence quenching of 1-hydroxypyrene-3,6,8-trisulfonic acid (HPTS) in the presence of single-walled carbon nanotubes (SWCNT) using a fluorescence method. To investigate the quenching mechanism (dynamic or static) of HPTS, Stern-Volmer plots of single walled carbon nanotubes at different temperatures were used. The positive deviation from linearity in Stern-Volmer plots suggests that single walled carbon nanotubes follow a static quenching mechanism evidenced by the formation of a stable ground state complex. The results presented here help us to clarify the quenching mechanism in the interaction of a pyrene derived dye and carbon nanotubes. This study will open new possibilities in the use of the conjugate formed by SWCNTs and HPTS in the fabrication of a<br />biosensor based on intracellular fluorescent probes.

Abstract An indirect spectrofluorometric probe method is developed for calculating equilibrium constants for formation of heterogeneous solvent-solvent molecular complexes from measured fluorescence emission intensities in select systems that exhibit parabolic-shaped Stern-Volmer quenching plots.

Selective spectrofluorometric sensing is introduced for the analysis of non-steroidal anti-androgens, darolutamide, and thalidomide in pharmaceutical preparations and biofluids. An organic fluorophore, 2,4,8,10-tetramethylpyrido[2′,3′:3,4]pyrazolo[1,5-a]pyrimidine 2 was synthesized in our laboratories by new simple methods to act as a fluorescent reagent for the analysis of the studied drugs. Elemental and spectral analyses were performed to approve the fluorophore structure. The fluorophore possesses a fluorescence at λem 422 nm when excited at 328 nm. The interaction between the studied drugs and the fluorophore was found to be quenching. The quenching mechanisms were studied and interpreted through the Stern–Volmer relationship. Moreover, the Stern–Volmer constants were calculated for the quenching interactions of both drugs. The introduced method was validated for the estimation of darolutamide and thalidomide in dosage forms, plasma, and urine, offering good percentage recoveries.

Este trabalho tem como objetivo sintetizar e caracterizar um novo complexo mononuclear de rutênio (III) e enrofloxacina (enro, fármaco antibacteriano da família das fluoroquinolonas), [Ru(enro)3].nH2O. Foram testadas várias rotas sintéticas e apenas a partir de uma delas obteve-se o composto desejado. O produto foi caracterizado pelas técnicas espectroscópicas de absorção na região do UV-visível e do infra-vermelho. Através desta última técnica foi possível determinar o modo pelo qual a enrofloxacina se coordena ao íon rutênio: a coordenação ocorre de modo bidentado através do oxigênio da piridona e do oxigênio do grupamento carboxilato. Outro objetivo deste trabalho foi investigar a interação do complexo mononuclear de rutênio (III) e norfloxacina, [Ru(nor)3].nH2O, com a albumina de soro humano (HSA), através da técnica de luminescência. Mais especificamente pelo estudo da supressão da luminescência dos resíduos de triptofano, aplicando-se o modelo de tratamento da supressão bimolecular de Stern-Volmer. O estudo de supressão de fluorescência mostrou, por meio de espectros de emissão da HSA, que com o aumento da concentração do complexo [Ru(nor)3].nH2O na solução de HSA, ocorre uma redução gradual da luminescência da HSA, devido a alterações da conformação da proteína, que sugerem alteração do microambiente próximos aos resíduos de triptofano. A partir do tratamento dos dados pode-se determinar tanto K_sv quanto a constante cinética do processo de supressão, que mostraram uma dependência com a temperatura sugerindo como mecanismo predominante de supressão o mecanismo dinâmico. Porém essa conclusão foi revista a partir da determinação dos tempos de vida do estado excitado da HSA, e pode-se concluir que o mecanismo predominante à temperatura ambiente é o mecanismo estático, porém com o aumento da temperatura ocorre a predominância do mecanismo do tipo dinâmico. Através da determinação dos parâmetros termodinâmicos, concluiu-se que as interações entre a HSA e o complexo são espontâneas, e forças de van der Waals e ligações de hidrogênio estão envolvidas na ligação entre a HSA e o supressor.
This work aims to synthesize and characterize a new mononuclear ruthenium (III) complex and enrofloxacin (enro, antibacterial drug of the fluoroquinolone family), [Ru(enro)3].nH2O. Several synthetic routes were tested, but only from one of them it was obtained the desired compound. The product was characterized by spectroscopic techniques of absorption in UV-visible and infra-red regions. Through this last technique, it was possible to determine the coordination mode of enrofloxacin to the ruthenium ion: the coordination occurs in a bidentate way through the pyridone oxygen and the oxygen of the carboxylate group. Another aim of this study was to investigate the interaction of mononuclear ruthenium (III) complex and the norfloxacin, [Ru(nor)3].nH2O, with the human serum albumin (HSA), through the technique of luminescence. More specifically, by the study of the quenching of luminescence of tryptophan residues, by applying the Stern-Volmers model of treatment of bimolecular suppression. The fluorescence quenching study showed, through the emission spectra of HSA, that increasing the complex concentration in HSA solution, there is a gradual reduction of the luminescence of HSA, due to the conformational changes of the protein that suggests the change of microenvironment near tryptophan residues. From the data processing it is possible to determine both K_sv and the kinetic constant of the suppression process, which showed temperature dependence, suggesting as the predominant mechanism of quenching the dynamic mechanism. However, this conclusion has been revised from the determination of the lifetimes of the excited state of HSA, and it can be concluded that the predominant mechanism at room temperature is the static mechanism, but with the temperatures increase, it occurs the predominance of the dynamic type mechanism. By determining the thermodynamic parameters, it was concluded that the interactions between HSA and the complex are spontaneous, and Van der Waals forces and hydrogen bonds are involved in the binding between HSA and suppressor.

Metallhalogenid-Perowskite (MHPs) sind Halbleiter, die einzigartige photophysikalische Eigenschaften aufweisen, die sie ideal für photovoltaische Anwendungen machen. Techniken werden kontinuierlich entwickelt, um die Leistungsgrenzen der Perowskite weiter zu verschieben. Dennoch weisen diese Materialien verschiedene Herausforderungen auf. Zu diesen gehören eine geringe Stabilität unter einer Vielzahl von äußeren Bedingungen, sowie eine große Diskrepanz zwischen den Wirkungsgraden von Geräten im Labormaßstab und großflächigen Geräten. Zunächst wurden mit Hilfe von Photolumineszenz-Spektroskopie Ladungsübertragungsmechanismen zwischen MHPs und atmosphärischen Gasen untersucht, um deren Einfluss auf die Materialstabilität zu bestimmen. Durch den Vergleich der Emission von verschiedene MHP wurde die Wirkung untersucht, die atmosphärische Gase auf Grenzdefekte im Material haben. Diese Löschungseffekte wurden nachfolgend mit dem Stern-Volmer-Modell analysiert. Es stellte sich heraus, dass ein Teil von der Gase bindet jedoch an die MHPs, wobei teilweise Kristalldefekte passiviert werden und für jedes der Gase Ladungstransfermechanismen vorgeschlagen wurden. Zweitens wurde die Skalierung von MHP-Bauelementen mittels Tintenstrahldruck untersucht. Dazu wurden drei Kristallisationstechniken ausgewertet. Eine davon verwendete eine sequenzielle Abscheidung von zwei Präkursortinten, während die beiden anderen kristallisierte Tinten verwendeten, die in einem Schritt abgeschieden wurden. Die letztgenannten Techniken verwendeten beide niedrige Drücke und bei einer wurde ein kontrollierter Stickstoffstrom auf die Probe angewendet. Solarzellen mit einer Effizienz von 16,8% auf einer Fläche von 0,16 cm² wurden demonstriert. Diese Ergebnisse zeigen ein neuartiges Verfahren zur Untersuchung von strahlungslosen Verlustwegen in MHPs auf. Zusätzlich demonstrieren diese Studien, dass der Tintenstrahldruck eine geeignete Technologie ist, um MHP-Bauelemente zu skalieren.
Metal halide perovskites (MHPs) are semiconductor materials that show unique photophysical properties, making them ideal for photovoltaic applications. Having shown power conversion efficiencies of up to 25.5%, techniques are continuously being developed to push perovskites to unprecedent limits. Yet, these materials present challenges like a low stability under a variety of conditions as well as a large disparity between the efficiencies of lab scale and large area devices. This thesis addresses these two major obstacles. First, charge transfer mechanisms between MHPs and atmospheric gases were studied to determine their effect on the material stability by using photoluminescence spectroscopy. By comparing the emission of MHPs, the effect that molecular oxygen, nitrogen, argon, and water have on boundary defects in the material was studied. These quenching effects were later analyzed using the Stern-Volmer model. It was found that the gases bounce off the surface, but a portion of them bind to the MHPs, in occasions passivating defects on the crystals. Using these results, charge transfer mechanisms were proposed for each one of the gases. Second, scaling of MHP devices was examined using inkjet printing. For this, three crystallization techniques were evaluated. One of them used sequential deposition of two precursor inks, while the other two crystallized ink that was deposited in one step. Both latter techniques used low pressures, below 1 mbar, and only one of them applied a controlled stream of nitrogen to the sample. Using these techniques, the deposition of a 15x15 cm² area as well as a device with an efficiency of 16.8% on an area of 0.16 cm² were demonstrated. These results show a novel procedure to study non-radiative loss paths in MHPs to enhance their stability and performance as devices. Also, they show that inkjet printing is a favorable technology to scale MHP devices and eventually facilitate the mass production of this type of photovoltaic devices.

Using luminescent exciton traps, an efficiency of the exciton migration in J-aggregates of pseudoisocyanine dye in solutions has been investigated. Applying a modified Stern-Volmer equation for an analysis of the J-aggregates luminescence quenching by the trap, the quenching of 50% of PIC J-aggregates luminescence at the ratio PIC/trap = 70:1 has been found. To increase the exciton migration efficiency, the Jaggregate structure was improved by the formation of a "J-aggregate-surfactant” complex. It results in 35% enhancement of the exciton migration efficiency in PIC J-aggregates. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35095

The subject of the present research deals with optical sensors for detecting oxygen. They are based on the quenching by oxygen of the luminescence of organometallic complexes embedded in polymeric matrixes. Excitation light is provided by a LED source and a photodiode is employed as detector. Optical sensor may substitute electrochemical ones, because they allow in situ, real time, non destructive measurements. They are more robust than electrochemical ones reducing the need of frequent calibration and membrane replacement. Attention has been focused on luminescence-intensity-based sensors, instead of lifetime-based ones, because they are more promising to build low cost industrial sensors. Final aim is the realization of a sensor working in a wide concentration range and up to 90°C. No commercial sensor with such characteristics is available. Stern Volmer model describes dynamic quenching, and oxygen concentration may be obtained from luminescence quenching according to: I0/I=1-K'sv*%O2 where I and τ are the luminescence intensity and excited-state lifetime of the luminophore, respectively. I0 and τ0 denote the same parameters in the absence of oxygen. The Stern Volmer constant K’SV is proportional to the luminophore lifetime in the absence of oxygen, τ0, oxygen diffusion coefficient in the polymeric membrane, and oxygen solubility into the membrane, . Various luminophores having various lifetimes in the absence of oxygen has been tested in order to optimize sensor analytical performances ruthenium tris-(4,7-diphenyl-1,10-phenanthroline) bis(octylsulphate) (Ru(dpp)OS, τ0=6μs), 5,10,15,20-Tetrakisphenyl-21H,23H-porphine platinum(II) (PtTPP, τ0=50μs), platinum 5,10,15,20-Tetrakis(pentafluorophenyl)-21H,23H-porphine platinum(II) (PtTFPP τ0=70μs), 5,10,15,20-Tetrakis(pentafluorophenyl)-21H,23H-porphine palladium(II) (PdTFPP, τ0=850μs) and 2,3,7,8,12,13,17,18-Octaethyl-21H,23H-porphine palladium(II) (PdOEP, τ0=990μs). They have been embedded in polysulfone (PSF) or polyvinylchloride (PVC). Dip-coating and spin-coating deposition procedures have been optimized. Stern Volmer model has been modified to take into account contributions to light intensity not considered in Stern Volmer model. In particular, a new procedure may determine light emission contribution from luminophores enclosed in sites where oxygen cannot enter. This correction allowed to demonstrate that curvatures of the SV calibration, often cited in the literature, come just from the cited contribution. In particular, SV calibration of three different PSF membranes embedding Ru(dpp)OS, PtTPP and PdTFPP, are linear. Luminophore degradation influence over luminescence drift has been analyzed, and a correcting algorithm has been developed. At 30°C, Ru(dpp)OS has a luminescence drift of -1,01•10-4 s-1 whilst, for porphyrins, it has been proved negligible at room temperature. Drift becomes more influent at higher temperature, because of luminophores thermal degradation. A PtTFPP-PSF sensor was studied in details to determine activation energies of the involved processes: Stern Volmer constant, K’SV, light emitted intensity in absence of oxygen, I0, and sensor response time, t1, have been determined at various temperature. Employing a suitable physical model like Arrhenius equation, free activation energies, ΔG‡, of diffusion and non radiative decays processes have been obtained. They are 2.8(0.3) kJ/mol and 16.5(0.5) kJ/mol, respectively. ΔH relative to the solubility in the membrane has been calculated too, obtaining 13(3) kJ/mol. Membrane sensitivity, K’SV, and maximum detectable oxygen percentage , has been calculated for various membranes. Most sensitive membranes are characterized by lower maximum detectable oxygen percentage. In order to extend the sensor working interval to higher oxygen percentages maintaining high sensitivity, two routes have been followed: 1) dynamic calibration; 2) construction of a “bi-label” sensor. 1) The dynamic calibration model is based on the transient intensity light profiles vs. time instead of equilibrium intensities. As theoretically demonstrated and experimentally confirmed, transient intensity during oxygen exit from the membrane has a sigmoidal shape. The parameters of this sigmoid do not vary with oxygen starting concentration, and the only variable is the inflection time, which may be employed as analytical quantity instead of equilibrium light intensity. The great advantage is that inflection point time may be determined for each %O2 value even with very sensitive membranes. Experimental verification has been performed on Ru(dpp)OS, PtTPP and PdTFPP membranes embedded in PSF. The precision of “classic” measurement, based on the light intensity measurement at equilibrium, is almost constant with increasing %O2, and equal to 3.5, 0.7 e 0.4 % for Ru(dpp)OS, PtTPP and PdTFPP, respectively. In dynamic calibration model, precision decreases with increasing %O2. The dynamic model is preferable to classical one for low oxygen concentration (less than 97%, 9.2%, e 7.2%, for membranes containing Ru(dpp)OS, PtTPP or PdTFPP, respectively). Classical measurements have been proved more sensitive than dynamic measurements for large oxygen percentages and membranes with high K’SV, while the opposite is valid for low oxygen percentages and membranes with low K’SV. The oxygen percentage where the two methods have the same sensitivity is 60%, 6% e 2% for Ru(dpp)OS, PtTPP and PdTFPP respectively. Dynamic calibration model is better than classical for low oxygen concentration determination and for application fields requiring an extended working range. Emission profiles measurement, however, is more complicated than equilibrium intensity measurement, and requires a reference gas (i.e. nitrogen) limiting its applicability in the portable sensor field. 2) A sensor embedding two luminophores in the same polymeric matrix (“bi-label sensor) has been prepared. Sensor behaviour has been theoretically rationalized and experimentally verified in two cases: Ru(dpp)OS and PtTPP embedded in PSF and PtTPP and PdTFPP embedded in PVC. The two luminophores have been demonstrated to behave independently into the matrix. A working graph has been obtained in order to predict optimal membrane composition to extend the working range up to required oxygen concentration optimizing sensor sensitivity. In the considered cases, for a working range from 0 to 100% , luminophores with K’SV near to 0.02 (K’SV (Ru(dpp)OS in PSF)= 0.014, K’SV(PtTPP in PVC)=0.019) and to 0.2 (K’SV (PtTPP in PSF)= 0.14, K’SV(PdTFPP in PVC)=0.27) have been chosen. Luminophores optimal molar fraction realized the condition that emission intensity fraction due to PtTPP is 0.45 e 0.31 of overall emitted intensity, for PSF and PVC, respectively. A commercial sensor prototype has been built. In order to obtain a robust sensor, whose response is not influenced by most of instrumental factors, pulsed light source have been employed to reduce photodegradation and optical fibers allowed to isolate light sources and detectors from temperature change in the analyzed mixture. A software has been developed in order to control simultaneously all the instruments (flow meters, oven, pulse generator, etc.) and to automate measurements and data elaboration. Sensors embedding PtTFPP have been tested continuously 24 hours a day for one month. If test is carried at room temperature, the luminescence decrease is close to 7.1% and measurement repeatability is very good. If the same test is carried at 90 °C, luminescence decrease is equal to 28.7% but measurement repeatability, using drift corrected calibration algorithm results very good. Finally, a portable sensor has been built for a particularly complex application: oxygen continuous monitoring in composting urban wastes, with temperature up to 80°C. Sensor precision, estimated from standard deviation, results <0.3% O2 for every oxygen concentration. Sensor accuracy, expressed as relative error of mixtures with known oxygen concentration, is always <4%.
L’argomento di ricerca sviluppato durante la Scuola di Dottorato è stato lo studio di sensori ottici per il monitoraggio dell’ossigeno molecolare. Il principio di funzionamento di questi sensori è dato dallo spegnimento della luminescenza di luminofori metallorganici inglobati in una matrice polimerica. La luminescenza viene indotta per eccitazione del luminoforo con una sorgente LED e è raccolta da un rilevatore a fotodiodo. I sensori basati su questo principio costituiscono una valida alternativa ai sensori elettrochimici attualmente in uso, in quanto permettono misure “in situ” e in tempo reale, ed in modo non distruttivo. Sono inoltre più robusti limitando sia la necessità di frequenti calibrazioni che la frequente sostituzione delle membrane. È stata focalizzata l’attenzione principalmente sui sensori che si basano sulla misura delle intensità luminose, piuttosto che su quella dei tempi di vita, in quanto più promettenti per realizzare sensori a basso costo adatti per applicazioni industriali. L’obiettivo finale è quello di realizzare un sensore robusto ed economico, in grado di misurare l’ossigeno in un ampio intervallo di concentrazioni e di sopportare temperature fino ai 90°C, condizione per la quale non esistono a tutt’oggi prodotti commerciali. Lo spegnimento della luminescenza è legato alla quantità di ossigeno molecolare a seguito di quenching, secondo il modello di Stern-Volmer (SV), da cui si ottiene la seguente relazione: I0/I=1-K'sv*%O2 dove con I0/I si indica il rapporto tra l’intensità luminosa emessa in assenza e in presenza di ossigeno e con τ0/τ l’analogo rapporto tra i tempi di vita nelle due situazioni. Questo rapporto è proporzionale alla percentuale di ossigeno %O2 secondo una costante K’SV che risulta proporzionale al tempo di vita in assenza di ossigeno, τ0, al coefficiente di diffusione dell’ossigeno nella membrana, e alla sua solubilità, . Al fine di ottimizzare le caratteristiche analitiche delle membrane sensibili sono stati testati svariati luminofori con differenti tempi di vita in assenza di ossigeno: Rutenio tris(4,7-difenil-1,10-fenantrolina) (Ru(dpp), τ0=6μs), Platino 5,10,15,20-tetrafenilporfirina (PtTPP, τ0=50μs), Platino-5,10,15,20-tetra(pentafluorofenil)porfirina (PtTFPP, τ0=70μs), Palladio5,10,15,20-tetra(pentafluorofenil)porfirina (PdTFPP, τ0=850μs) e Palladio2,3,7,8,12,13,17,18-ottaetilporfirina (PdOEP τ0=990μs). Questi luminofori sono stati inglobati all’interno di polimeri organici: polisulfone (PSF) e polivinilcloruro (PVC). Sono state ottimizzate le procedure di deposizione sia per spin-coating che per dip-coating, . E’ stata introdotta una modifica al modello di SV, al fine di scorporare dal valore di emissione sperimentale i contributi non contemplati dal modello di SV. In particolare la nuova procedura permette di scorporare il contributo di emissione attribuibile alla parte di luminoforo all’interno della membrana non raggiungibile dall’ossigeno. Questa modifica ha permesso di constatare che la curvatura della calibrazione di SV documentata in diversi lavori riportati in letteratura è dovuta al citato contributo. Operando in questo modo è stata dimostrata la linearità del modello di SV per tre differenti tipologie di membrane utilizzate, contenenti differenti luminofori (Ru(dpp), PtTPP e PdTFPP) inglobati in PSF e caratterizzate da differenti K’SV (0.014, 0.136, 1.79). È stato poi analizzato l’effetto della deriva dell’intensità luminosa nel tempo, dovuta a fenomeni di degradazione del luminoforo, sviluppando un algoritmo di correzione di tali effetti. È stato osservato che il complesso del rutenio presenta una deriva significativa del segnale di -1,01•10-4 s-1 a 30 °C, mentre per tutte le porfirine essa è risultata di due ordini di grandezza più bassa. Il problema della deriva diviene fondamentale quando si considera il funzionamento del sensore ad alte temperature, situazioni nelle quali il contributo della termodegradazione del luminoforo può diventare rilevante. Lo studio di questi sistemi ha permesso di ricavare alcune importanti caratteristiche chimico-fisiche come le energie di attivazione dei differenti processi coinvolti. A questo scopo è stato studiato specificamente il comportamento dell’emissione di un sensore contenente PtTFPP inglobata in PSF. Dalle misure dell’andamento della costante di Stern-Volmer (K’SV), dell’intensità di emissione (I0) e del tempo di risposta (t1) al variare della temperatura, utilizzando opportuni modelli fisici quali l’equazione di Arrhenius, sono state ricavate le energie libere di attivazione (ΔG‡) dei processi di diffusione e di decadimento radiativo che sono risultate pari a 2.8(0.3) kJ/mole e 16.5(0.5) kJ/mol, rispettivamente. E’ stato determinato inoltre il ΔH relativo alla solubilità dell’ossigeno all’interno della membrana polimerica, risultato pari a 13(3) kJ/mol. Oltre alla determinazione della sensibilità di calibrazione è stato determinato il limite massimo di misura di differenti membrane. Le membrane con K’SV elevati presentano limiti massimo di misura più bassi. Per estendere l’intervallo di lavoro verso l’alto senza dover rinunciare completamente a un’elevata sensibilità sono state seguite due vie: 1) calibrazione dinamica; 2) sistema “bi-label”. 1) La prima via sfrutta un modello di calibrazione “dinamico” che non si basa sulle intensità in condizioni di equilibrio bensì sulla forma dei profili di intensità nel tempo. E’ stato dimostrato teoricamente e confermato con dati sperimentali che la forma transiente dell’intensità durante l’uscita dell’ossigeno dalla membrana ha la forma di una sigmoide. La forma di tale sigmoide è indipendente dalla concentrazione di ossigeno da cui si parte, e l’unica cosa che varia è la posizione nel tempo del punto di flesso, che può quindi essere utilizzata come grandezza sperimentale diagnostica al posto dell’intensità luminosa. Il vantaggio è che la posizione del punto di flesso è misurabile a qualunque livello di concentrazione anche per membrane molto sensibili. La verifica di questo modello è stata effettuata su membrane contenenti Ru(dpp), PtTPP o PdTFPP inglobati in PSF. E’ stato dimostrato che le misure “classiche”, basate sulla misura delle intensità all’equilibrio, hanno una precisione approssimativamente costante all’aumentare della %O2 e mediamente pari al 3.5, 0.7 e 0.4 %, rispettivamente. Con il modello dinamico di calibrazione essa è invece decrescente con l’aumentare della %O2. Da questo punto di vista esso è preferibile rispetto al modello classico per basse concentrazioni di ossigeno (inferiori al 97%, 9.2%, e 7.2%, per membrane contenenti Ru(dpp), PtTPP o PdTFPP, rispettivamente). Per quanto riguarda la sensibilità è stato determinato che le misure “classiche”, risultano più sensibili rispetto alle misure secondo il metodo dinamico da noi sviluppato per membrane con elevate K’SV e a alte %O2, mentre la situazione si inverte per basse K’SV e %O2. Una sensibilità equivalente dei due metodi di misura si ottiene per %O2 pari al 60%, 6% e 2% per membrane contenenti Ru(dpp), PtTPP o PdTFPP, rispettivamente. Il metodo dinamico di calibrazione risulta quindi preferibile, oltre che per le applicazioni che richiedono un intervallo di lavoro esteso al di fuori di quello consentito dal metodo “classico”, anche per misure di basse concentrazioni di ossigeno. Per contro, la misura del profilo di emissione è più laboriosa rispetto a quella della misura diretta dell’intensità emessa in condizioni e richiede l’utilizzo di un gas di riferimento (generalmente azoto), limitando le prospettive di applicazione nel campo dei sensori portatili. 2) Il secondo approccio ha portato alla realizzazione di un sensore contenente due luminofori inglobati nella stessa matrice. È stato razionalizzato il comportamento di tali sensori dal punto di vista teorico e ne sono state verificate le caratteristiche sperimentalmente per due casi studio: una miscela di Ru(dpp) e PtTPP in PSF e una di PtTPP e PdTFPP in PVC. E’ stato dimostrato che, all’interno della matrice, i due luminofori si comportano indipendentemente tra di loro. In questo modo è stato possibile ricavare un grafico di lavoro che predice le composizioni ottimali per ottenere sensori in grado di effettuare misure in un intervallo di concentrazioni prestabilite, ottimizzando la sensibilità. Nei casi considerati, volendo ottenere sensori in grado di monitorare tutto l’intervallo 0-100 , sono state scelte coppie di luminofori con K’SV vicine a 0.02 (K’SV (Ru(dpp) in PSF)= 0.014, K’SV(PtTPP in PVC)=0.019) e a 0.2 (K’SV (PtTPP in PSF)= 0.14, K’SV(PdTFPP in PVC)=0.27). La frazione molare ottimale dei due luminofori deve essere scelta in modo che la frazione di intensità luminosa emessa dalla PtTPP nelle due membrane sensibili sia pari a 0.45 e 0.31 per PSF e PVC, rispettivamente. Lo studio effettuato ha permesso di realizzare un prototipo di sensore per un utilizzo commerciale. Le caratteristiche ricercate di massima robustezza e indipendenza da fattori strumentali della misura dell’intensità luminosa, sono state ottenute mediante l’uso di sorgenti pulsate per ridurre la fotodegradazione dello strato sensibile e di fibre ottiche per isolare le sorgenti LED ed i rivelatori a fotodiodo dalle variazioni di temperatura dell’ambiente di misura. È stato inoltre sviluppato un software in grado di controllare simultaneamente le diverse strumentazioni necessarie (flussimetri, generatore di segnale, termostato, ecc.) e di automatizzare sia le misure sia i calcoli necessari per gestire e monitorare il comportamento dei sensori durante i test di prova, che sono consistiti in calibrazioni in continuo per 24 ore al giorno e per 30 giorni. Al termine del test a temperatura ambiente su membrane contenenti PtTFPP in PSF si è osservato un calo medio dell’intensità luminosa del 7.1%, e un’ottima ripetibilità delle misure. A 90°C il calo di intensità per membrane analoghe è stato decisamente superiore, pari al 28.7%, ma una volta corretto con l’algoritmo sopra menzionato la ripetibilità delle misure è risultata comunque ottima. E’ stato infine realizzato e testato un prototipo di sensore adatto alle prove sul campo, in particolare per un’applicazione particolarmente complessa che prevede il monitoraggio in continuo dell’ossigeno in una massa di rifiuto umido in fase di compostaggio, nella quale si può raggiungere la temperatura di 80°C. La precisione del sensore è stata stimata dalla deviazione standard sulla mediana delle misure, ottenendo valori inferiori a 0.3% O2 per ogni livello di concentrazione. Come stima dell’esattezza è stato preso l’errore relativo della misura di miscele a titolo noto, ottenendo valori inferiori al 4%.

The first part of this dissertation deals with the application of a luminescence quenching method to measure diffusion and permeation coefficients of oxygen in polymers. Most luminescence oxygen sensors do not follow linearity of the Stern-Volmer (SV) equation due to heterogeneity of luminophore in the polymer matrix, thus the complexity of data analysis is increased. To circumvent this limitation, inverted fluorescence microscopy is utilized in this work to investigate the SV response of the sensors at the micron-scale. In these diffusion experiments, oxygen concentration is measured by luminescence changes in regions with high SV constants and good linearity. Thus, we avoid numerical complexity of combining nonlinear SV equation with a diffusion model. This technique allows us to measure oxygen diffusion properties in different type of polymers like transparent, opaque, free-standing polymers and polymers that cannot be cast into free standing films and polymer composites. In the second part of this thesis, we have explored the effect of Ag-Cu alloy nanoparticles on the emission intensity of luminophores at their close proximity. Alloy nanoparticles offer additional degrees of freedom for tuning their optical properties by altering atomic composition and atomic arrangement and thus can be an attractive option for manipulating signal of a wide range of luminophores. In this work, surface plasmon resonance spectrum of Ag-Cu alloy nanoparticles deposited by sputtering was easily tuned in wide wavelength range by varying one experimental condition- annealing temperature. Large metal enhanced luminescence for different luminophores viz Alexa Fluor 594 and Alexa Fluor 488 were achieved at the vicinity of Ag-Cu nanoparticles when maximum spectral overlap between SPR spectra of Ag-Cu nanoparticles and the emission and absorption spectra of the luminophores occur. We also studied the effect of composition of Ag-Cu nanoparticles synthesized by the polyol process on the luminescence of low quantum yield dye Cy3. In the third part of this thesis, quenching effect of Cu nanoparticles on CdSe/ZnS nanocrystal quantum dots has been explored. As Cu nanoparticles have comparable dielectric properties with gold nanoparticles, they are expected to show similar quenching effects. It was found that Cu is an efficient quencher of fluorescence from CdSe/ZnS quantum dots and the quenching effect is due to resonance energy transfer from quantum dots to Cu nanoparticles.

Mesure du niveau de conduction d'alcanes et de cycloalcanes par difference de travaux de sortie metal/liquide, metal/vide de photocathodes en zinc ou en or irradiees par photons uv. Mise en evidence du role des etats de surface. Determination du seuil d'ionisation par photoionisation de liquides avec des photons de 7 a 10 ev. Comparaison des courbes a la theorie d'onsager. Etude de la nature des etats precurseurs a la paire separee ion-electron

碩士
中原大學
化學研究所
102
The main objective of this study is to investigate the adsorption of azo dyes (methyl red isomers and methyl orange) on metal-organic frameworks (MOFs) by measuring the variation of fluorescence intensity. Because of the adsorption of dyes by MOFs, the fluorescence intensity is decreased with increasing concentration of the dyes. The fluorescence measurement is further analyzed by using the Stern-Volmer equation. Dynamic quenching constant (KD) and the fluorescence lifetime (τ) are calculated in order to understand the dye fluorescence quenching ability of MOFs. The results revealed that the methyl red molecule, due to the steric hindrance of the carboxylate functional group at different position, has been adsorbed differently on MOFs, therefore the quenching capability is also different. In the excitation wavelength dependence study, though the fluorescence excitation using 270 nm is weaker compared with using 350 nm, we can still observe the fluorescence quenching of dye at 270 nm. Finally, Raman spectroscopy was also performed in order to verify the adsorption orientation of the dye adsorbed on MOFs. We have demonstrated that the results of Raman spectroscopy and fluorescence quenching are consistent. In addition to fluorescence spectroscopy, we have used the UV-visible spectroscopy, Raman spectroscopy, and time-correlated single photon counting system.The results &; discussion of these studies are included in this thesis.

碩士
中原大學
化學研究所
105
In this study, fluorescence spectroscopy was used to investigate fluorescence quenching between metal–organic frameworks (MOFs) consisting of Al centers and methyl red isomers (ortho, para, and meta). After the methyl red dyes had been adsorbed onto the metal-organic frameworks, the intensity of their fluorescence decreased as the concentration of the dye increased. The effects of the molecular structure on the fluorescence quenching were investigated using the same MOF with different methyl red dyes, or the same methyl red dye with different MOFs. When methyl red isomers were used as fluorescence quenchers, non-linear trends were observed in the CYCU-4(Al) DUT-4(Al), MIL-69(Al), and MIL-100(Al) Stern-Volmer plots. The reason for this is related to the structural properties of the MOFs and methyl red, e.g. variations in MOF ligand and differences in the substituent positions of the methyl red isomers. In addition, the non-linear curves of the Stern-Volmer plots indicated that dynamic and static fluorescence quenching between methyl red and the MOFs occurred simultaneously. Finally, to improve our understanding of the quenching behaviors of MOFs and methyl red, the temperature effect was used to differentiate the dynamic and static quenching behaviors. If the slope of the Stern-Volmer plots increased as the temperature increased, the quenching behavior was dominated by dynamic quenching. Conversely, if the slope decreased as temperature increased, then the quenching behavior was dominated by static quenching. The results will be discussed in detail in this paper.

The drug binding to protein is an attractive research topic. In order to assess the release of RxAc-CsNPs and their binding with lysozyme under physiological conditions, nanocomposite materials based on chitosan (Cs) and Roxatidine acetate (RxAc) in the presence Tween 80 (Tw80) surfactant were developed. The addition of Tw80 to CsNPs increased RxAc release in vitro. In this work, Stern–Volmer plot and thermodynamic results indicated that the mechanism of Lyz with RxAc and Lyz with RxAc-CsNPs was static mechanism and the main forces in both systems were hydrogen bonding and Van der Waals forces, which indicated that the binding reaction in both systems is spontaneous, exothermic and enthalpically driven. Synchronous fluorescence and CD results indicated that the RxAc and RxAc-CsNPs cause change in the secondary construction of Lyz. It was also found that the addition of Tw80 affects the binding constant of drug with protein. Finally, the molecular docking results have also been in accordance with the results of other techniques. Hence, the developed RxAc loaded Chitosan nanoparticles could be used as an effective strategy for designing and application of the antiulcer drugs. Altogether, the present study can provide an important insight for the future designing of antiulcer drugs.

In this study, we developed a carbon-dot-based sensor, which is particularly sensitive to ascorbic acid. It was possible to generate carbon dots (CDs) by utilising a renewable resource: Curcuma longa, which is abundantly available. The carbon dots produced from curcuma longa have particle diameters of 0.6 nm and are extremely brilliant in appearance. It has been proven that the fluorescence of carbon dots is inhibited in the presence of dopamine and ascorbic acid, with dopamine being more sensitive to the fluorescence than ascorbic acid. There were no significant differences between the minimal detection limits for dopamine and ascorbic acid, which were 33 μM, respectively. The Stern-Volmer plot was used to establish the quenching of ascorbic acid. It is one of the potential technique for sensing ascorbic acid.

Relaxation and quenching of excited states of Br2 in CC14 is studied by time-resolved photothermal grating combined with near-IR fluorescence. A slow rise in diffraction transient signals from photothermal gratings, due to nonradiative relaxation of excited states, is observed for Br2 in CC14. Near-IR fluorescence measurement reveals that there are two decay components; the fast component has a lifetime about 6 ns, and the slower component has a lifetime around 20 ns, depending on Br2 concentration and oxygen content in the sample. The slower component is assigned to the decay of A' state. From the amplitudes of thermal grating, the quantum yield of the A' state formation is estimated to be 0.33+0.03. Stern-Volmer plot of the measured decay rate of A' state, including results obtained from both near-IR fluorescence and photothermal grating measurement, suggests that quenching of A' state proceeds initially at diffusion-limited rate at low concentration and reduces to nondiffusion-limited at higher concentration. Possible mechanisms for the observed decrease of quenching rate as concentration increases are also discussed.