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This paper addresses the electronic states and physicochemical properties of non-steroidal anti-inflammatory drug (NSAID) namely: Ibuprofen, Ketoprofen and Flufenamic acid. The molecular structures are quantum chemically treated and geometrically optimised using density functional theory (DFT). The computed geometrical parameters are compared with the experimental data. The Mulliken charge analysis is accomplished to understand the partial charge distribution in molecules. The molecular electrostatic potential analysis has been used to identify the appropriate location for an electrophilic and nucleophilic attacking site. Frontier molecular orbitals of the molecules are estimated and analysed. The HOMO-LUMO energy gaps have been used to estimate the different global reactivity descriptors of the selected molecules under investigation. The FT-IR spectra of molecules are recorded experimentally and are computed using DFT. The potential energy distribution (PED) assignment for the computed vibrations is carried out. The NBO analysis has been used to find the most intensive interaction in molecules based on the Fock-matrix sta3bilization energy. The NLO parameters have been computed for molecules to check their suitability towards NLO based applications. The UV-absorption spectra and ADME parameters for titled molecules are also simulated.

Spectral properties of laser dyes 4-methyl-7-(4-morpholinyl)-2H-pyrano[2,3-b]-pyridin-2-one (LD-425) and 6,7,8,9tetrahydro-6,8,9-trimethyl-4-(trifluoromrthyl)-2H-pyrano[2,3b][1,8]naphthyridin-2-one (LD-489) have been investigated in the temperature range 25[degrees]C-65[degrees]C by steady-state and transient methods. Fluorescence intensity decreases with increase in temperature, with fluorescence band maxima shifted towards shorter wavelengths in both dyes. Furthermore, fluorescence lifetime has decreased with increase in temperature for LD-425, whereas it remained constant with change in temperature for LD-489. The possible deactivation mechanisms are discussed. The quenching effect of these dyes in the presence of aniline at different temperatures has been studied and the Stern-Volmer (S-V) plots are nonlinear, showing positive deviation. It has been observed that the dynamic quenching constant increases with temperature, whereas the static quenching constant is independent of temperature. Key words: LD-425, LD-489, fluorescence quenching, lifetime, activation energy. Par methodes d'etats stationnaires et transitoires, nous etudions les proprietes spectrales des colorants laser 4-methyle-7-(4-morpholinyle)-2H-pyrano[2,3-b] pyridine-2-un (LD-425) et 6,7,8,9-tetrahydro-6,8,9-(trifluoromethyle)- 2H-pyrano[2,3][1,8]naphthyridine-2-un (LD-489) dans le domaine de temperature 25 [degrees]C-65 [degrees]C. L'intensite de la fluorescence diminue avec l'augmentation de temperature et la bande de florescence est deplacee vers les longueurs d'onde plus courtes dans les deux colorants. De plus, le temps de vie de fluorescence diminue avec l'augmentation de temperature pour le LD-425, alors qu'il demeure constant pour le LD-489. Nous analysons les possibles mecanismes de desactivation a differentes temperatures et les graphiques de Stern-Volmer (S-V) montrent des deviations non lineaires, indiquant une deviation positive. Nous observons que la constante de desactivation dynamique augmente avec la temperature, alors que la constante de desactivation statique est independante de la temperature. [Traduit par la Redaction] Mots-cles : LD-425, LD-489, desactivation de fluorescence, temps de vie, energie d'activation., 1. Introduction The interaction of fluorescence, optical properties, and temperature in organic fluorophores is an increasing field of interest in biomedical applications. The optical properties modulate fluorescence and comprise part [...]

The fluorescence quenching of 1, 2, 3, 8-tetrahydro-1, 2, 3, 3, 8-pentamethyl-5-(trifluoromethyl)-7H-pyrrolo[3, 2-g]quinolin-7-one (LD-473) by aromatic amines, namely, aniline, dimethyl aniline, and diethyl aniline, in methanol, ethanol, propanol, and butanol has been studied at room temperature using steady-state and time-resolved methods. A positive deviation from linearity has been observed in 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 the dielectric constant of alcohols. The quenching ability of amines increases with increasing 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 combined effect of both dynamic and static quenching processes. PACS Nos.: 32.50+d, 33.50-j, 33.50Hv, 33.50Dq, 42.62Fi. Nous etudions a la temperature de la piece, par methode stationnaire et a temps resolu, l'extinction de la fluorescence du 1, 2, 3, 8-tetrahydro-1, 2, 3, 3, 8-pentamethyle-5(trifluoromethyle)-7H-pyrrolo[3, 2-g]hydroxy-7-un (LD-473) par des amines aromatiques, nommement l'aniline, l'aniline dimethyle et l'aniline diethyle dans le methanol, l'ethanol et le butanol. Nous observons une deviation positive de la linearite dans les graphiques de Stern-Volmer (S-V). Differents parametres de taux d'extinction sont determines en utilisant l'equation etendue de S-V et nous trouvons qu'ils dependent de la constante dielectrique de l'alcool. La capacite d'extinction des amines augmente avec l'augmentation de leur energie d'ionisation. De plus, en utilisant le modele d'extinction statique a l'interieur d'une sphere d'activite, avec l'approximation du puits fini, nous en concluons que les reactions d'extinction bimoleculaire sont dues a l'effet combine des mecanisme statique et dynamique d'extinction. [Traduit par la Redaction], 1. Introduction Fluorescence quenching is widely used as a probe in many bio-analytical applications [1]. An appropriate fluorophore-quencher combination provides useful information about a particular bio-analytical system. The phenomenon of [...]

The energy transfer using two laser dyes 6,7,8,9-tetrahydro-6,8,9-trimethyl-4-(trifluoromethyl)-2H -pyrano[2,3-b][1,8] naphthyridin-2-one (LD-489) and 1,2,3,8-tetrahydro-1,2,3,3,8-pentamethyl-5 -(trifluoromethyl)-7H-pyrrolo[3,2-g]quinolin-7-one (LD-473) as donors and rhodamine 6G (Rh6G) as acceptor was investigated in methanol using steady state and time resolved fluorescence spectroscopy. The bimolecular quenching rate parameter, [k.sub.q], and the translation diffusion rate parameter, [k.sub.d], were calculated and these values indicated that the diffusion process alone does not operate in energy transfer process. The mean diffusion length, [d.sub.1], is found to be less than the Furster distance, [R.sub.o], supporting the dominance of long-range interaction. The critical transfer distances determined from both the Furster equation and the half quenching concentration are close to one another, revealing that the Furster mechanism plays an important role in overall energy transfer of the donors. PACS Nos.: 33.50.Dq, 33.20.-t, 42.62.Fi, 33.15.Hp. En utilisant la spectroscopie par fluorescence stationnaire et a resolution temporelle, nous etudions le transfert d'energie entre deux colorants a laser, en solution dans le methanol, comme donneurs. Les donneurs sont le 6,7,8,9-tetrahydro6,8,9-trimethyl-4-(trifluoromethyl)-2H-pyrano[2,3-b][1,8]naphthyridine-2-un (LD-489) et le 1,2,3,8-tetrahydro-1,2,3,3,8-pentamethyle5-(trifluoromethyl)-7H-pyrrolo[3,2-g]hydroxy-7-un (LD-473) et le receveur est ici la rhodamine 6G (Rh6G). Nous calculons le parametre du taux d'extinction bimoleculaire, [k.sub.q], et le parametre du taux de diffusion par translation, [k.sub.d], et ces valeurs indiquent que la diffusion n'agit pas seule dans le processus de transfert d'energie. Nous trouvons que la longueur moyenne de diffusion, [d.sub.1], est plus courte que la distance de Furster, [R.sub.o], suggerant qu'une interaction a grande portee domine le mecanisme. La distance de transfert critique determinees a l'aide de l'equation de Furster est proche de celle obtenue de la concentration a mi-extinction, ce qui signifie que le mecanisme de Furster joue un role important dans le transfert global d'energie provenant des donneurs. [Traduit par la Redaction], Introduction Fluorescence resonance energy transfer (FRET) is the transfer of the excited state energy from a donor (D) to acceptor (A). This transfer occurs without the appearance of a photon [...]

The interaction of silver nanoparticles with four laser dyes, namely, LD-425, LD-489, LD-473, and LD-423, dispersed in methanol has been studied at room temperature by absorption and fluorescence spectroscopy. The silver nanoparticles were synthesized by chemical reduction and estimated size is 11 nm according to Mie theory. The changes in absorption spectrum of these dyes with the addition of silver nanoparticles suggest possible interaction with the silver nanoparticles. The magnitudes of the association constants are estimated using the Benesi-Hildebrand model. Fluorescence quenching has been observed for all the dyes with the addition of silver nanoparticles of different concentrations. The Stern-Volmer plots of fluorescence quenching in the case of LD-425 and LD-489 are found to be linear, suggesting the fluorescence quenching is because of the dynamic quenching process. But in the case of LD-473 and LD-423, the Stern-Volmer plots are nonlinear showing positive deviation and the fluorescence quenching in these dyes is because of static quenching processes. Also, it is found that the fluorescence quenching is not solely due to diffusion. PACS Nos.: 33.20.-t, 33.50.Dq, 36.40.Mr, 78.67.Bf, 82.80.Dx. Utilisant la spectroscopie par absorption et fluorescence a la temperature de la piece, nous etudions l'interaction de nanoparticules d'argent avec quatre colorants, nommement le LD-425, le LD-489, le LD-473 et le LD-423 dans du methanol. Les nanoparticules sont synthetisees par reduction chimique et leur grosseur estimee est de 11 nm selon la theorie de Mie. Les changements dans le spectre d'absorption de ces colorants, suivant l'ajout de nanoparticules, suggere une interaction possible avec les nanoparticules d'argent. Nous estimons la valeur des constantes d'interaction a l'aide de la methode de Benesi-Hildebrand. Nous observons une extinction de la fluorescence pour tous les colorants suite a l'ajout de nanoparticules d'argent a differentes concentrations. Les graphiques de Sturm-Volmer de l'extinction de fluorescence sont lineaires dans les cas de LD-425 et LD-489, ce qui suggere un mecanisme d'extinction dynamique. Ils sont non lineaires avec deviation positive dans les cas de LD-473 et LD-423, ce qui suggere un mecanisme statique d'extinction. Nous trouvons egalement que l'extinction de fluorescence n'est pas due exclusivement a la diffusion. [Traduit par la Redaction], Introduction Metal nanoparticles have been a subject of great interest because of their potential applications in electronics, nonlinear optics, chemical and biochemical sensors, and in catalysis [1]. Because of surface [...]

In this manuscript, a complete theoretical and experimental investigation of antibiotic agents Sulfamethoxazole (SMX) and Trimethoprim (TMP) was performed at B3LYP, CAM-B3LYP, B3PW91/6-311++G (d,p) levels through DFT (density functional theory). The bond length and bond angles of SMX and TMP are calculated and compared with existence literature data. The global reactivity descriptors have been estimated from HOMO - LUMO energies to understand the stability and chemical reactivity of investigated molecules. The electrophilic sites present in the investigated molecules have been identified by using MEP. Mulliken atomic charge distribution has been analysed at three different levels of theories/basis set. The Non-linear optical parameters have been calculated for investigated molecules to understand their suitability in non-linear optics. The NBO study has been utilised to disclose the strongest inter-molecular interactions. The vibrational assignment of SMX and TMP molecules has been performed with the assistance of DFT coupled with the VEDA program. [ABSTRACT FROM AUTHOR]

The effect of temperature (20-60 °C) on the fluorescence emission of (E)-N-(3-chlorophenyl)-2-(3,4,5- trimethoxybenzylideneamino)-4,5,6,7-tetrahydrobenzo [b]thiophene-3carboxamide (ENCTTTC) is studied in different solvents. It is found that there is no shift in the position of fluorescence maxima, but the intensity decreases with increasing temperature, which depends on the polarity of the solvent. A mechanism of fluorescence quenching with rise in temperature is discussed in terms of the relative location of lowest (ππ*) (nπ*) states and the energy difference between them. The change in temperature brings about a change in the probabilities of radiative and nonradiative transition. The nonradiative deactivation of excited states in the absence of a quencher is temperature dependent and its thermal activation energy has been determined. PACS Nos.: 33.50.-j, 33.50.D, 33.50.Hv, 33.50.Dq. Nous etudions dans differents solvants les effets de la temperature (20-60°C) sur l'emission fluorescente de (E)-N-(3-chlorophenyl)-2-(3,4,5-trimethoxybenzylideneaimino)-4,5,6,7-tetrahdrobenzo[b]thiophene-3carboxiamide (ENCTTTC). Nous trouvons qu'il n'y a aucun deplacement dans la position des maxima de fluorescence, mais l'intensite decroit avec l'augmentation de la temperature, qui depend de la polarite du solvant. Nous discutons du mecanisme d'extinction de la fluorescence avec l'augmentation de la temperature, en fonction de la localisation des plus bas etats (ππ*) (nπ*) et de la difference en energie entre eux. La variation en temperature change les probabilites de transition radiative et non radiative. La desactivation non radiative de l'etat excite en l'absence de desactivateur depend de la temperature et nous determinons l'energie thermale d'activation. [Traduit par la Redaction], 1. Introduction The effect of temperature on the fluorescence emission intensity of many organic compounds has been discussed extensively for the derivatives of coumarin, indole, anthracene, and rohdamine [1-20]. It [...]

Quenching mechanisms of coumarin dyes, namely 6-bromo-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarin (6BDTC) and 8-methoxy-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarin (8MDTC), were carried out in toluene by adopting two methods, namely steady-state and time-resolved methods, to understand the role of diffusion in the quenching mechanism. The solute molecules were excited by UV radiation of wavelength 360 and 330 nm. Various quenching parameters like frequency of encounter ([k.sub.d]), probability of quenching per encounter (p and p=), and quenching rate parameter (kq and k'q) were experimentally determined in all the solvents. Activation energy of quenching ([E.sub.a] and [E.sub.a]) was also determined by using the literature values of activation energy of diffusion ([E.sub.d]). It was found that the values of [E.sub.a] (and [E.sub.a]) were less than [E.sub.d] indicating that the quenching reactions are more significantly influenced by diffusion. PACS Nos.: 33.50.D, 33.50.-j, 87.64.i, 31.70.Hq. A l'aide des methodes stationnaire et resolue dans le temps, afin de comprendre le role de la diffusion dans le mecanisme d'extinction (de luminescence), nous avons active dans le toluene les mecanismes d'extinction de colorants coumarine, nommement le 6-bromo-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarine (6BDTC) et 8-methoxy-3-[1-(4,5- dicarbomethoxy-1,2,3triazoloacetyl)]coumarine (8MDTC). Les molecules de solute ont ete excitees par radiation UV de longueur d'onde 360 et 330 nm. Nous avons determine experimentalement, dans tous les solvants, differents parametres de desactivation, comme la frequence de collision ([k.sub.d]), la probabilite de desactivation par collision (p et p=) et le parametre de taux de desactivation (kq et kq). Utilisant les valeurs de la litterature pour l'energie d'activation de la diffusion ([E.sub.d]), nous avons determine les energies d'activation de desactivation ([E.sub.a] et [E.sub.a]). Nous trouvons que [E.sub.a] (et [E'.sub.a)] sont plus petites que [E.sub.d], ce qui indique que les reactions de desactivation sont significativement plus affectees par la diffusion. [Traduit par la Redaction], 1. Introduction The mechanism of decreasing the fluorescence intensity of a given substance is known as fluorescence quenching. The different types of quenching mechanisms are dynamic quenching, static quenching, and [...]

The solvatochromic studies in a Quinoline derivative molecule namely Quinolin-8-ol (QO) have been carried out at ambient temperature using absorption and fluorescence spectroscopy. The QO molecule shows the bathochromic shift with increase in solvent polarity demonstrating π → π* transition. The solvatochromic data coupled with quantum mechanical calculations has been used to estimate change in dipole moment of the molecule after excitation. It has been found that excited state dipole moment is greater than the corresponding ground state dipole moment. Further, it is observed that excited and ground state dipole moments are parallel. The chemical reactivity and kinetic stability of QO molecule are investigated using Frontier molecular orbital (FMO) analysis. Natural bond orbital (NBO) analysis shows proton transfer within the selected donor-acceptor depicting large energy of stabilization for QO molecule. The calculated Fukui functions infer the local softness and local eletrophilicity index of QO molecule. The theoretically simulated UV-Vis absorption spectrum of QO molecule matches well with the experimental spectrum. [ABSTRACT FROM AUTHOR]

Inferable from the significance of solvent mixtures in practical chemistry, toluene (TL) and butanol (BL) mixtures are used to studyfluorescence behavior of boronic acid dye 2-methoxy-5-fluoro-phenyl boronic acid (2MEFPBA). At the inception, preferential solvation is examined in TL-BL, to understand specific and nonspecific interactions. Suppan's dielectric enrichment model is further used to understand the nonideality and dielectric enrichment in TL-BL mixtures for preferential solvation. Bimolecular quenching reaction studies of 2MEFPBA with aniline as quencher are made in mixtures of TL-BLto know the effect of viscosity and dielectric constant variation at room temperature. The quenching process is studied in all solvent mixtures by steady state and transient state method. Quenching is characterized by S-V plots having upward curvature. Analysis of modified S-V equations which accounts both static and dynamic quenching allows calculating bimolecular quenching rate constant. The bimolecular quenching reactions are found to be significantly larger. Further finite sink approximation model is invoked so as to check whether reactions are diffusion limited. The extents of these rate parameters demonstrate that positive deviations in the Stern-Volmer (S-V) plot are because of the presence of apparent static and dynamic quenching process. [ABSTRACT FROM AUTHOR]

The spectral behavior of two ketocyanine dyes 2,5-di[(E)-1-(4-dimethylaminophenyl) methylidine]-1-cyclopentanone(2,5-DMAPMC) and 2,5-di[(E)-1-(4-diethylaminophenyl) methylidine]-1-cyclopentanone (2,5-DEAPMC) is investigated in the presence of silver nanoparticles (AgNPs) of sizes 32 nm, 52 nm and 60 nm using absorption and fluorescence spectroscopy. The absorption spectral changes of dyes with the addition of AgNPs of different sizes suggest their possible interaction with AgNPs. Fluorescence quenching has been observed for both the dyes with the addition of AgNPs of all the sizes. The possible quenching mechanisms including energy transfer and electron transfer are discussed. The fluorescence quenching rate parameter is found to increase with increase in the size of AgNPs and is explained based on the varying ability of silver AgNPs of different sizes to accommodate dye molecules. The effect of functional groups on quenching rate parameters is also discussed. [ABSTRACT FROM AUTHOR]

The effect of plasmonic silver nanoparticles' size on photophysical characteristics of four biologically active 4-aryloxymethyl coumarins 4-p-tolyloxymethylbenzo[h] coumarin (4PTMBC), 1-(4-iodo phenoxymethyl)-benzo [f] coumarin (1IPMBC), 4-(4-iodo-phenoxymethyl)-benzo [h] coumarin (4IPMBC), and 4-(4-iodo-phenoxymethyl)- 6-methoxy coumarin (4IPMMC) has been studied using absorption and fluorescence spectroscopy. The size of silver nanoparticles has been estimated by field effect scanning electron microscope technique. The absorption maxima of silver nanoparticles are red shifted with increase in their size. The absorption spectral changes of investigated coumarins with the addition of silver nanoparticles of different sizes suggest their possible interaction with silver nanoparticles. Fluorescence quenching has been observed for all the coumarins with the addition of silver nanoparticles of different sizes. The Stern-Volmer (S-V) plots of fluorescence quenching are found to be linear. The magnitude of quenching rate parameter suggests the involvement of static quenching mechanism. Fluorescence data has been used to estimate binding constants and the number of binding sites. The contribution of diffusion and electron transfer processes in fluorescence quenching mechanism has also been discussed. The values of S-V constant and quenching rate parameter are found to decrease with increase in size of silver nanoparticles. [ABSTRACT FROM AUTHOR]

The effect of solvents of varying polarity and hydrogen bonding ability, solvent mixture and silver nanoparticles on the photophysical properties of a ketocyanine dye, 2,5-di[( E)-1-(4-diethylaminophenyl) methylidine]-1-cyclopentanone (2,5-DEAPMC), is investigated at room temperature. Solvent effect is analyzed using Lippert-Mataga bulk polarity function, Reichardt's microscopic solvent polarity parameter, and Kamlet's and Catalan's multiple linear regression approaches. The spectral properties better follow Reichardt's microscopic solvent polarity parameter than the Lippert-Mataga bulk polarity function. This indicates that both general and specific solute-solvent interactions are operative. Kamlet's and Catalan's multiple linear regression approaches indicate that polarizability/dipolarity solvent influences are greater than hydrogen bond donor and hydrogen bond acceptor solvent influences. The solvatochromic correlations are used to estimate excited state dipole moment using the experimentally determined ground state dipole moment. The excited state dipole moment of the dye is found to be larger than its corresponding ground state dipole moment and ground and excited state dipole moments are not parallel, but subtend an angle of 77°. The absorption and emission spectra are modulated in the presence silver nanoparticles. The fluorescence of 2,5-DEAPMC is quenched by silver nanoparticles. The possible fluorescence quenching mechanisms are discussed. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The photophysical properties of 4-fluoro-2-methoxyphenyl boronic acid (4FMPBA) are characterized using absorption and fluorescence techniques in series of non-alcohols and alcohols. The results are analyzed using different solvent polarity functions and Kamlet and Catalan's multiple regression approaches. The excited state dipole moment and change in dipole moment are calculated using both the solvatochromic shift method and Reichardt's microscopic solvent polarity parameter [ABSTRACT FROM AUTHOR]

The effect of solvents of varying polarity on the absorption and fluorescence emission of the Schiff base, 2-{[3-(1H-benzimidazole-2-yl) phenyl]carbonoimidoyl}phenol, was studied using Lippert-Mataga bulk polarity function, Reichardt's microscopic solvent polarity parameter and Kamlet's multiple linear regression approach. The spectral properties follow Reichardt's microscopic solvent polarity parameter better than Lippert-Mataga bulk polarity parameter, indicating the presence of both general solute-solvent interactions and specific interactions. Catalan's multiple linear regression approach indicates the major role of solvent polarizability/dipolarity influence compared with solvent acidity or basicity. The solvatochromic effect was utilized to calculate the dipole moments of ground and excited states of the Schiff base using different methods. Bathochromic shift in the emission spectrum and the increase in dipole moment in the excited state signifies the intramolecular charge transfer character in the emitting singlet state. Fluorescence quenching by aniline was also studied in 1,4-dioxane and n-butanol, and the results were analyzed using sphere of action static quenching and finite sink approximation models. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Physics is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Physics is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Fluorescence quenching of 1,3-diphenyl benzene (m-terphenyl) by carbon tetrachloride (CCl4) at steady state in different solvents, namely n-hexane, n-heptane, cyclohexane, toluene, benzene acetonitrile, 1,4-dioxane, and with a transient method in benzene has been done at room temperature to understand the role of quenching mechanisms. The Stern-Volmer plot was found to be linear for all the solvents studied. The probability of quenching per encounter p was determined in all the solvents and was found to be less than unity. Further, from the studies of rate parameters and lifetime measurements in benzene at different temperatures (30-60°C), it was shown that the phenomenon of quenching is generally governed by the well-known Stern-Volmer (S-V) plot. The activation energy Ea (E'a) of quenching was determined using literature values of activation energy of diffusion Ed, and it was found to be greater than Ed, which confirms the fact that the quenching mechanism is not solely due to material diffusion but there is also contribution from activation energy. [ABSTRACT FROM AUTHOR]

Abstract: The fluorescence quenching of 1, 4-bis[2-(2-methylphenyl)ethenyl]-benzene (Bis-MSB) in toluene has been studied with carbon tetrachloride (CCl4) and aniline by steady-state and transient methods. A positive deviation was observed in the Stern–Volmer (S–V) plot for both the quenchers. This indicates the presence of either static or transient quenching component in the overall dynamic quenching. The experimental data are analysed by sphere of action static quenching model. The value of radius of sphere of action determined from this model is greater than the sum of the radii of the Bis-MSB and respective quenchers. 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. This fact suggests the simultaneous presence of static and dynamic component in the fluorescence quenching Bis-MSB by CCl4 and aniline. [Copyright &y& Elsevier]

The influence of pure solvent and binary solvent mixtures on the optical properties of non-steroidal anti-inflammatory drug (NSAID) molecule, specifically flufenamic acid (FLA), has been studied using absorption and fluorescence spectroscopic techniques. A bathochromic shift is observed in the emission wavelength of FLA with an increase in the solvent polarity of pure solvents, attributed to the highest stability of the excited state. The spectral properties are correlated with Lippert–Mataga, solvent polarity parameter, Kamlet, and Catalan solvent polarity parameters, suggesting that both general and specific solvent effects influence the spectral properties, with general solvent effects dominating over specific solvent effects. Preferential solvation studies have been carried out in tetrahydrofuran (THF) and water solvent mixture, revealing variations in the preference for solvation of FLA as a function of the mole fraction of water. Solvatochromic data are utilized to estimate the excited state dipole moment in pure solvents using different solvatochromic methods, revealing that the excited state dipole moment of FLA is higher than its ground state counterpart. The increase in dipole moment in the excited state compared to the ground state is explained based on intramolecular charge transfer (ICT), with elaboration and discussion on the possible resonance structure corresponding to ICT, inferring the more polar nature of the excited state compared to the ground state. The effect of solute polarizability on the excited state dipole moment and change in dipole moment is also discussed. [ABSTRACT FROM AUTHOR]

The role of silver nanoparticles on spectroscopic properties of biologically active coumarin dyes 4-p-tolyloxymethyl-benzo[ h ]coumarin (4PTMBC) and 1-(4-iodophenoxymethyl)-benzo[ f ]coumarin (1IPMBC) has been investigated using absorption and fluorescence spectroscopy. Silver nanoparticles are synthesized by chemical reduction method and the estimated size by Mie theory is 12 nm. The absorption spectral changes of dyes in the presence of silver nanoparticles suggest their possible interaction with silver nanoparticles. The apparent association constants of the interaction are estimated using Benesi–Hildebrand model. Fluorescence quenching has been observed in both the dyes with the addition of silver nanoparticles. The Stern–Volmer plots of fluorescence quenching are found to be nonlinear showing positive deviation. The magnitudes of quenching rate parameter and fluorescence lifetime measurements indicate the presence of both collisional and static quenching mechanisms. The binding constants and the number of binding sites for the static type of quenching have been estimated from the fluorescence data. The role of diffusion, energy transfer and electron transfer processes in fluorescence quenching mechanism has been discussed. [ABSTRACT FROM AUTHOR]

The effect of temperature (20-60 °C) on the fluorescence emission of (E)-N-(3-chlorophenyl)-2-(3,4,5-trimethoxybenzylideneamino)-4,5,6,7-tetrahydrobenzo [b]thiophene-3carboxamide (ENCTTTC) is studied in different solvents. It is found that there is no shift in the position of fluorescence maxima, but the intensity decreases with increasing temperature, which depends on the polarity of the solvent. A mechanism of fluorescence quenching with rise in temperature is discussed in terms of the relative location of lowest (ππ*) (nπ*) states and the energy difference between them. The change in temperature brings about a change in the probabilities of radiative and nonradiative transition. The nonradiative deactivation of excited states in the absence of a quencher is temperature dependent and its thermal activation energy has been determined. [ABSTRACT FROM AUTHOR]

Quenching mechanisms of coumarin dyes, namely 6-bromo-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarin (6BDTC) and 8-methoxy-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarin (8MDTC), were carried out in toluene by adopting two methods, namely steady-state and time-resolved methods, to understand the role of diffusion in the quenching mechanism. The solute molecules were excited by UV radiation of wavelength 360 and 330 nm. Various quenching parameters like frequency of encounter ( kd), probability of quenching per encounter ( p and p′), and quenching rate parameter ( kq and ) were experimentally determined in all the solvents. Activation energy of quenching ( Ea and ) was also determined by using the literature values of activation energy of diffusion ( Ed). It was found that the values of Ea (and ) were less than Ed indicating that the quenching reactions are more significantly influenced by diffusion. [ABSTRACT FROM AUTHOR]

The effect of titanium dioxide (TiO 2 ) nanoparticles (NPs) on photophysical characteristics of 2,5-di[(E)-1-(4-dimethylaminophenyl) methylidine]-1-cyclopentanone (2,5-DMAPMC) and 2,5-di[(E)-1-(4-diethylaminophenyl)methylidine]-1-cyclopentanone (2,5-DEAPMC) ketocyanine dyes has been studied using absorption, steady-state and time-resolved fluorescence spectroscopy. The magnitudes of association constants determined based on modified absorption spectrum of dyes due to the presence of TiO 2 NPs indicate the interaction of TiO 2 NPs with dye molecules. The quenching of fluorescence intensity of dyes by TiO 2 NPs is observed and it follows linear Stern-Volmer (S-V) equation. The magnitude of quenching rate parameter suggests the involvement of static quenching mechanism. The involvement of electron transfer process in reducing fluorescence intensity of dyes has been discussed. Also, varying influence of TiO 2 NPs on two dyes is explained based on the presence of different alkyl substituent in two dyes., (Copyright © 2017 John Wiley & Sons, Ltd.)

The effect of solvents of varying polarity and hydrogen bonding ability, solvent mixture and silver nanoparticles on the photophysical properties of a ketocyanine dye, 2,5-di[(E)-1-(4-diethylaminophenyl) methylidine]-1-cyclopentanone (2,5-DEAPMC), is investigated at room temperature. Solvent effect is analyzed using Lippert-Mataga bulk polarity function, Reichardt's microscopic solvent polarity parameter, and Kamlet's and Catalan's multiple linear regression approaches. The spectral properties better follow Reichardt's microscopic solvent polarity parameter than the Lippert-Mataga bulk polarity function. This indicates that both general and specific solute-solvent interactions are operative. Kamlet's and Catalan's multiple linear regression approaches indicate that polarizability/dipolarity solvent influences are greater than hydrogen bond donor and hydrogen bond acceptor solvent influences. The solvatochromic correlations are used to estimate excited state dipole moment using the experimentally determined ground state dipole moment. The excited state dipole moment of the dye is found to be larger than its corresponding ground state dipole moment and ground and excited state dipole moments are not parallel, but subtend an angle of 77°. The absorption and emission spectra are modulated in the presence silver nanoparticles. The fluorescence of 2,5-DEAPMC is quenched by silver nanoparticles. The possible fluorescence quenching mechanisms are discussed. Copyright © 2016 John Wiley & Sons, Ltd., (Copyright © 2016 John Wiley & Sons, Ltd.)