Effect of Solvent Polarity on Fluorescence Quenching of New Indole Derivatives by CCl4

ABSTRACT

The fluorescence quenching of solutes 3-[5′-methyl-3′-phenylindol-2′-yl]-s-triazolo [3,4-b] [1,3,4] thiadiazol-6(5H)-thione (MPITTT) and 3-phenyl-2,5-bis-[thiosemicarbazido] indole (PbisTI) by carbon tetrachloride (CCl₄) in dioxane and acetonitrile mixtures has been studied at room temperature by steady-state fluorescence measurements. The positive deviation from linearity has been observed in the Stern–Volmer (S-V) plots for both fluorophores in different composition of mixed solvents even at moderate CCl₄ concentration (0.10 mol dm^?3). Various quenching parameters of the quenching processes have been determined using the extended S-V equation and have been found to be dependent on the solvent polarity. Further, with the use of the finite sink approximation model, it is concluded that the bimolecular quenching reactions are diffusion limited, and the distance parameter R′ and mutual diffusion coefficient D are estimated independently.     

Fluorescence quenching of newly synthesized biologically active coumarin derivative by aniline in binary solvent mixtures

The fluorescence quenching of newly synthesized coumarin (chromen-2-one) derivative, 4-(5-methyl-3-furan-2-yl-benzofuran-2-yl)-7-methyl-chromen-2-one (MFBMC) by aniline in different solvent mixtures of benzene and acetonitrile was determined at room temperature (296 K) by steady-state fluorescence measurements. The quenching is found to be appreciable and positive deviation from linearity was observed in the Stern-Volmer (S-V) plots in all the solvent mixtures. This could be explained by static and dynamic quenching models. The positive deviation in the S-V plot is interpreted in terms of ground-state complex formation model and sphere of action static quenching model. Various rate parameters for the fluorescence quenching process have been determined by using the modified Stern-Volmer equation. The sphere of action static quenching model agrees very well with experimental results. The dependence of Stern-Volmer constant K_SV, on dielectric constant ε of the solvent mixture suggests that the fluorescence quenching is diffusion-limited. Further with the use of finite sink approximation model, it is concluded that these bimolecular quenching reactions are diffusion-limited. Using lifetime (τ_o) data, the distance parameter R′ and mutual diffusion coefficient D are estimated independently.     

Fluorescence Quenching of 2,2″-dimethyl-p-terphenyl by Carbon Tetrachloride in Binary Mixtures

The fluorescence quenching of 2,2″-dimethyl-p-terphenyl (DMT) by carbon tetrachloride (CCl₄) was investigated in different solvent mixtures of benzene and acetonitrile at room temperature (300 K). A positive deviation from linearity was observed in the Stern-Volmer plots for all the solvent mixtures. This could be explained satisfactorily by static and dynamic quenching models. The nonlinearities in the S-V plots are interpreted in terms of ground state complex model and the sphere of action static quenching model. The results suggest that positive deviations in the S-V plot are due to the presence of both static and dynamic quenching processes. To explain that bimolecular reactions are diffusion limited, we have used finite sink approximation model. Various rate parameters for the quenching process have been determined by static and dynamic quenching models. The dynamic quenching constant depends on the solvent polarity and indicates that quenching reaction is diffusion limited.     

A study on fluorescence quenching of LD-425 by aromatic amines in 1,4-dioxane–acetonitrile mixtures

The fluorescence quenching of 4-methyl-7-(4-morpholiny)-2H-pyrano[2,3-b]pyridin-2-one (LD-425) by aromatic amines aniline (AN), dimethyl aniline (DMAN) and diethyl aniline (DEAN) in solvent mixtures of 1,4-dioxane and acetonitrile has been studied at room temperature by steady-state and time-resolved methods. The positive deviation from linearity has been observed in the Stern–Volmer (S–V) plots. Various quenching rate parameters have been determined using the extended S–V equation and are found to be dependent on solvent polarity. The quenching ability of amines increases with increase in their ionization energies. Further, with the use of the sphere of action static quenching model and finite sink approximation model, it is concluded that the bimolecular quenching reactions are due to the presence of both dynamic and static quenching processes.     

Role of solvent polarity on the fluorescence quenching of newly synthesized 7,8-benzo-4-azidomethyl coumarin by aniline in benzene-acetonitrile mixtures

The fluorescence quenching of 7,8-benzo-4-azidomethyl coumarin by aniline has been studied in different solvent mixtures of benzene (BN) and acetonitrile (AN) at room temperature. The quenching is found to be appreciable and a positive deviation from linearity was observed in the Stern-Volmer (S-V) plot in all the solvent mixtures. Various parameters for the quenching process have been determined by sphere of action static quenching model and finite sink approximation model. The magnitudes of these rate parameters indicate that positive deviation in the S-V plot is both due to static and dynamic processes.     

Effect of solvent on the quenching of fluorescence of safranine T(3,7-diamino-2,8-dimethyl-5-phenylphenazinium chloride) in binary solvent mixtures

Fluorescence quenching of 3,7-diamino-2, 8-dimethyl-5-phenylphenazinium chloride (safranine T (ST)) by halides and pseudo halides in binary solvent mixtures was investigated by steady-state fluorescence spectroscopy. Several parameters, such as dielectric constant, viscosity coefficient, and fluorescence quantum yield have been investigated as a function of solvent compositions. In mixed solvents ST has been used as a probe for studying the microheterogenity of the mixture. The preferential solvations around ST in the excited state were determined. The Stern-Volmer quenching constants at different compositions of solvent mixtures were determined and the rational analysis of the results was attempted.     

醌对卟啉荧光猝灭的溶剂效应

测定了在室温和未脱氧条件下不同浓度的苯醌(BQ)对卟啉衍生物四苯基卟吩(TPP),四苯基卟吩锌(ZnTPP)激发一重态的猝灭.由猝灭而引起的荧光强度的变化和荧光寿命的变化均可用Stern-Volmer关系式描述.由此根据寿命计算出的猝灭常数均比据荧光强度计算出的猝灭常数小.这是由于荧光强度测量中的自吸收效应引起的.实验结果表明;猝灭常数Kq与溶剂极性无关而只与粘度有关.说明这种猝灭是受扩散控制的动态猝灭.动力学分析表明,这是一种强猝灭,电荷转移猝灭速度比卟啉和醌的复合物的分解速度大或与之相近.比较实验结果和我们以前及其他作者发表的结果后,可以得出结论.苯醌对卟啉衍生物激发态电荷转移猝灭的溶剂效应随分子状态的不同而异:分子内的和通过三重态进行的分子间电荷转移猝灭受溶剂极性影响,但通过一重态进行的分子间电荷转移猝灭则与溶剂极性无关.     

Tuning the Solution Phase Photophysics of Two De Novo Designed Hydrogen Bond Sensitive 9-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-one Derivatives

Two new fluorophores, 6,7-dimethoxy-9-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-one (DMTCO) and 5-methyl-8,9-dihydro-5H-[1,3]dioxolo[4,5-b]carbazol-6(7H)-one (MDDCO), first of their kind, have been synthesized from the corresponding methoxy and methylenedioxy derivatives of 2,3,4,9-tetrahydro-1H-carbazol-1-one respectively. Comprehensive photophysical characterization of these compounds has been carried out in sixteen different homogeneous solvents and binary solvent mixtures. Both of these compounds are sensitive to solvent polarity, but the sensitivity is much higher in electronic excited state observed by steady-state and time-resolved fluorescence experiments than in ground state studied by UV–vis absorption spectroscopy. The fluorescence spectral shifts are linearly correlated with the empirical parameters of the protic solvents and also the quantitative influence of the empirical solvent parameters on the emission maxima of the compounds has been calculated. The change in dipole moment of the compounds in their excited state has been calculated from the shifts in corresponding emission maxima in pure solvents. A higher dipole moment change of both DMTCO and MDDCO in protic solvents is due to intermolecular hydrogen bonding which is further confirmed by the comparison of their behaviour in toluene-acetonitrile and toluene-methanol solvent mixtures. From structural features, MDDCO is more planar compared to DMTCO, which is reflected better in fluorescence quenching of the former with organic bases, N,N-dimethylaniline and N,N-diethylaniline. Laser flash photolysis experiments prove that the quenching interaction originates from photoinduced electron transfer from the bases to the compounds.     

Solvent Exchange in Excited-State Relaxation in Mixed Solvents

The fluorescence of styrylthiazoloquinoxaline (STQ) in the solvent mixture methanol and dichloromethane (DCM) and 2-octanol have many common characteristics: biexponential fluorescence decay, wavelength-dependent amplitudes, a negative amplitude for the short-lifetime component at long emission wavelengths, and a time-dependent red shift of the emission spectrum. In octanol, the fluorescence lifetime decreases with increasing temperature, whereas the lifetime increases with temperature in the methanol/DCM mixture. The fluorescence characteristics in 2-octanol ( = 7.29 cP) are readily explained by the conventional model of excited-state relaxation kinetics by solvent reorientation. This model is not applicable for low-viscosity ( = 0.455 cP) solvent mixtures. A model of excited-state relaxation kinetics involving solvent exchange (versus solvent reorientation in pure solvents) in the excited state is proposed for the solvent mixture. The model assumes that the solvent compositions around the solute are different in the ground and excited states and the solvent composition is temperature dependent.     

Static and dynamic quenching of biologically active coumarin derivative by aniline in benzene-acetonitrile mixtures

The fluorescence quenching of coumarin derivative, 4-(5-chloro-3-furan-2-yl-benzofuran-2-yl)-6-methyl-2H-chromen-2-one (ClFBMC), in the presence of aniline in different proportion of benzene-acetonitrile mixture was studied by means of steady-state measurement (296 K). The quenching process was characterized by Stern-Volmer (S-V) plots, which display positive (upward) deviation. The positive deviation from linearity suggests that the quenching is due to the simultaneous presence of dynamic and static quenching, which is interpreted in terms of the ground-state complex formation and the sphere of action static quenching model. The sphere of action static quenching model agrees very well with experimental results. Further with the use of finite sink approximation model, it is concluded that the bimolecular quenching reactions are diffusion-limited. Various rate parameters for the fluorescence quenching process have been determined. The value of quenching constant k_q increases with increase in dielectric constant of the mixed solvent, suggesting the charge transfer character of the excited complex.     

Determination of the diffusion and viscosity coefficients from the properties of dual fluorescence of molecules in solutions

We have proposed and substantiated an approach that makes it possible to determine the diffusion and microviscosity coefficients in solutions from characteristics of the dual fluorescence of molecular probes. This approach uses the Stern-Volmer constants obtained upon fluorescence dynamic quenching in solutions. The relations that follow from the balance equations in terms of the formalism of two-level reactions in the excited state for the case of photoreactions of the kinetic character yield the dependences of the intensity ratio of the fluorescence bands of the normal form and tautomer on the degree of quenching. In accordance with these dependences, the dynamic quenching of the diffusion character (including the temperature quenching) changes the intensity distribution, and, based on these dependences, the Stern-Volmer constants and the bimolecular quenching constants can be determined, from which, using appropriate models, the diffusion and viscosity coefficients can be found. The merit of the method is its simplicity and availability, since it is based on the use of the data of steady-state measurements of fluorescence spectra with widespread standard instruments.     

Quenching mechanisms of 5BAMC by aniline in different solvents using Stern–Volmer plots

The fluorescence quenching of 5,6 benzo-4-azidomethyl coumarin (5BAMC) by aniline in five different solvents namely benzene, dioxane, tetrahydrofuran, acetonitrile and dimethylformamide has been carried out at room temperature with a view to understand the quenching mechanisms. The Stern–Volmer (S–V) plot has been found to be nonlinear with a positive deviation for all the solvents studied. In order to interpret these results, we have invoked the ground-state complex formation and sphere of action static quenching models. Using these models various quenching rate parameters have been determined. The magnitudes of these parameters suggest that sphere of action static quenching model agrees well with the experimental results. Hence the positive deviation is attributed to the static and dynamic quenching. Further, with the use of finite sink approximation model, it was possible to check these bimolecular reactions as diffusion limited and to estimate independently distance parameter R′ and mutual diffusion coefficient D. Finally, an effort has been made to correlate the values of R′ and D with the values of the encounter distance R and the mutual coefficient D determined using the Edward's empirical relation and Stokes–Einstein relation.     

Fluorescence quenching of 2,2″ dimethyl-p-terphenyl by carbon tetrachloride in different solvents and temperatures

The fluorescence quenching of 2,2″-dimethyl-p-terphenyl (DMT) by carbon tetrachloride by steady state in different solvents, and by transient method in benzene has been carried out at room temperature. The Stern-Volmer (SV) plot has been found to be non-linear with a positive deviation for all the solvents studied. In order to interpret these results we have invoked the ground state complex and sphere of action static quenching models. Using these models various rate parameters have been determined. The magnitudes of these parameters imply that sphere of action static quenching model agrees well with the experimental results. Hence the positive deviation in the SV plots is attributed to the static and dynamic quenching. Further, from the studies of temperature dependence of rate parameters and lifetime measurements, it could be explained that the positive deviation is due to the presence of a small static quenching component in the overall dynamic quenching. With the use of finite sink approximation model, it was possible to check whether these bimolecular reactions as diffusion limited and to estimate independently distance parameter R′ and mutual diffusion coefficient D. Finally an effort has been made to correlate the values of R′ and D with the values of the encounter distance R and the mutual diffusion coefficient D determined using the Edward's empirical relation and Stokes-Einstein relation.     

Bimolecular quenching of fluorescence and interaction between excited molecules in solution

Bimolecular quenching of fluorescence was observed for fluoranthene, coronene and 3,4-benzophenanthrene in 1,2,4-trichlorobenzene or tetrahydrofuran solution, and the rate constant of the process was determined at various temperatures between room temperature (295 K) and 77 K. The bimolecular quenching rate constant was found to be a little smaller than that for a diffusion-controlled process in a fluid solvent. From the temperature dependence of the rate constant the quenching was found to be due to the long-range interaction which is enhanced by diffusion of the excited molecules in fluid media.     

Electronic spectroscopy of highly-polar aromatics. V. The polar excimer of N,N-dialkyl-p-cyanoaniline

The fluorescence spectra of N, N-dialkyl-p-cyanoanilines in fluid media have been re-examined. The long-wavelength fluorescence, previously attributed to a solvated ¹L_a → ¹A₁ fluorescence, is interpreted as an excimer fluorescence, an assignment which is supported by concentration dependence studies and quenching experiments. The temperature dependence of the excimer/ monomer fluorescence intensity ratio indicates that excimer formation is a diffusion controlled process. The binding energy of the excimer is found to be independent of the nature of the solvent and to be smaller than those values estimated for excimers of polycyclic aromatic hydrocarbons. Solvent viscosity, solvent polarity and specific solvent-solute interactions affect the excimer/monomer fluorescence intensity and these effects are interpreted. The geometry of the excimer is also discussed.     

Photophysical studies of xanthene dye in alkanols and in presence of inorganic ions

Eosin Y belongs to a xanthene group. It is an anionic fluorescent dye. The absorbance and fluorescence of Eosin Y have been investigated in a series of alkanols (methanol to propanol). When the solvents are added to the aqueous solution of Eosin Y (EY) the absorbance and fluorescence intensity are enhanced. The alkanols are found to affect the absorption and fluorescence spectra of the dye. On the basis of solvent adsorption model the binding constants of the dye with alkanols have been estimated. The interaction of solvent molecule with dye in aqueous solution is specific in nature. The fluorescence quenching of Eosin Y by the inorganic ions [Fe(CN)₆]⁻³, [Fe(CN)₆]⁻⁴ and Cl⁻ was also observed. The ions influenced the quenching process to different extents. The rate constants of quenching were calculated using the Stern-Volmer equation. The equilibrium constant of dye in presence of inorganic ions are determined by Scott equation.     

Temperature-Induced Swelling of Alkali Metal Polyacrylate Gels in Aqueous Organic Solvent Mixtures

It has been known that some polyelectrolyte systems, e.g., betaine polymer and polycations, have an upper critical solution temperature (UCST) in water while polyanions seldom show such a temperature-dependent phase separation. Recently we have found a significant counterion- and solvent-specific UCST-type behavior for alkali metal poly(acrylate)s (PAAM) in aqueous organic solvent mixtures. Namely, the reduced viscosity significantly increased with increasing temperature which was ascribed to disintegration of the ion-clusters or the aggregated ion-pairs formed at the lower temperature. In the present study, we prepared PAAM gel samples by irradiating the aqueous solutions with γ-rays in variable doses to find that a significant gel swelling was induced by a temperature jump from 5 to 40°C in various kinds of aqueous organic solvent mixtures. The UCST-type behavior and the counterion- and solvent-specificities for the gel swelling turned out to be parallel to those for the corresponding solution systems. In addition to these expected results, an appreciable LCST-type deswelling was unexpectedly observed for collapsed gels in a relatively higher solvent concentration region. Further, the γ-ray doses, i.e., the degree of crosslinking, proved to affect the UCST behavior; the gel swelling ratio was more significant for gels prepared with higher doses.     

Solvent and pH Effects on the Fluorescence of 7-(Dimethylamino)-2-Fluorenesulfonate

A novel water-soluble solvatochromic molecule, 7-(dimethylamino)-2-fluorenesulfonate (2,7-DAFS), was prepared by a three-step reaction from 2-nitrofluorene in good overall yield. The pH and solvent effects on the UV-VIS absorption and fluorescence spectra of 2,7-DAFS have been studied. Protonation of the dimethylamino group switches the absorption from intramolecular charge-transfer (ICT) to π → π* transition. The ground state pKa value of 2,7-DAFS was determined as 4.51. The fluorescence spectrum of the excited basic form, *(DAFS), shows a structureless single band with a large Stokes shift, whereas that of the acidic form, *(⁺HDAFS), exhibits a structured band with a small Stokes shift. The emission intensities of the basic and acidic forms versus pH/Ho plots show stretched sigmoidal curves and indicate that (1) the rate of deprotonation of *(⁺HDAFS) is comparable to the fluorescence decay of the species, and (2) the efficient proton-induced quenching of *(DAFS) fluorescence occurs. The pKa* was estimated as −1.7 from the fluorescence titration curve. The fluorescence maximum of *(DAFS) is blue-shifted as the polarity of solvent decreases. However, no clear dependency of the emission intensity and spectral half width, and thus fluorescence quantum yield, on the solvent polarity was revealed. It appears that the fluorescence sensitivity of 2,7-DAFS is 15 ∼ 25 times greater than the sensitivity of a widely utilized fluorescent probe, 5-(dimethylamino)-1-naphthalenesulfonate. This higher sensitivity, together with the ease of derivatization, would provide the fluorene-based fluorescent molecules significant advantages for a variety of applications.     

Reductive Fluorescence Quenching of the Photoexcited Free Base <Emphasis Type="Italic">meso</Emphasis>-Tetrakis (Pentafluorophenyl) Porphyrin by Amines

Steady state and time resolved fluorescence quenching behaviors of meso-Tetrakis (pentafluorophenyl) porphyrin (H₂F₂₀TPP) in presence of different aliphatic and aromatic amines have been executed in homogeneous dichloromethane (DCM) solution. At room temperature in DCM, free base (H₂F₂₀TPP) shows fluorescence with two distinct peaks at 640 and 711 nm and natural lifetime τ _f = 9.8 ns which are very similar to that of meso-tetraphenyl porphyrin (TPP). Unlike TPP, addition of both aliphatic and aromatic amines to a solution containing H₂F₂₀TPP results in an efficient decrease in fluorescence intensity without altering the shape and peak position of fluorescence emission. Upon addition of amines there was no change in optical absorption spectra of H₂F₂₀TPP. The fluorescence quenching rate constants ranged from 1 × 10⁹ to 4 × 10⁹ s⁻¹, which are one order below to the diffusion control limit, and temperature dependent quenching rate constants yield the activation energies which are found to be order of 0.1 eV. Femto second transient absorption studies reveal the existence of amine cation radical and porphyrin anion radicals with very short decay time (15 ps). The fluorescence quenching reaction follows Stern–Volmer kinetics. Steady state and time-resolved data are interpreted within general kinetic scheme of Marcus semi-classical model which attributes bimolecular electron transfer process between amines and the lowest excited singlet state of H₂F₂₀TPP. Calculated internal reorganization energies are found to be in between 0.04 and 0.22 ev. Variation of electron transfer rate as function of free energy change (∆G⁰) points the ET reactions in the present systems are in Marcus normal region. This is the first example of reductive fluorescence quenching of free base neutral porphyrins in homogeneous organic solvent ever known.     

Solvent effect on the fluorescence quenching of biologically active carboxamide by aniline and carbon tetrachloride in different solvents using S–V plots

The fluorescence quenching studies of carboxamide namely (E)-N-(3-Chlorophenyl)-2-(3,4,5-trimethoxybenzylideneamino)-4,5,6,7 tetrahydrobenzo[b]thiophene-3-carboxamide [ENCTTTC] by aniline and carbon tetrachloride in six different solvents namely toluene, cyclohexane, n-hexane, n-heptane, n-decane and n-pentane have been carried out at room temperature with a view to understand the quenching mechanisms. The Stern–Volmer (S–V) plots have been found to be non-linear with a positive deviation for all the solvents studied. In order to interpret these results we have invoked the ground state complex formation and sphere of action static quenching models. Using these models various quenching rate parameters have been determined. The magnitudes of these parameters suggest that sphere of action static quenching model agrees well with the experimental results. Hence the positive deviation is attributed to the static and dynamic quenching. Further, with the use of Finite Sink approximation model, it was possible to check these bimolecular reactions as diffusion-limited and to estimate independently distance parameter R′ and mutual diffusion coefficient D. Finally an effort has been made to correlate the values of R′ and D with the values of the encounter distance R and the mutual coefficient D determined using the Edward's empirical relation and Stokes Einstein relation.