Electron Transfer from Aromatic Amines to Excited Coumarin Dyes: Fluorescence Quenching and Picosecond Transient Absorption Studies (original) (raw)
Related papers
Journal of Molecular Structure, 2008
Electron transfer (ET) reactions between excited coumarin dyes and different aliphatic amine (AlA) and aromatic amine (ArA) donors have been investigated in acetonitrile solution using steady-state (SS) and time-resolved (TR) fluorescence quenching measurements. No ground state complex or emissive exciplex formation has been indicated in these systems. SS and TR measurements give similar quenching constants (k q) for each of the coumarin-amine pairs, suggesting dynamic nature of interaction in these systems. On correlating k q values with the free energy changes (DG 0) of the ET reactions show the typical Rehm-Weller type of behavior as expected for bimolecular ET reactions under diffusive condition, where k q increases with ÀDG 0 at the lower exergonicity (ÀDG 0) region but ultimately saturate to a diffusion-limited value ðk DC q Þ at the higher exergonicity region. It is, however, interestingly observed that the k DC q values vary largely depending on the type of the amines used. Thus, k DC q is much higher with ArAs than AlAs. Similarly, the k DC q for cyclic monoamine 1-azabicyclo-[2,2,2]-octane (ABCO) is distinctly lower and that for cyclic diamine 1,4-diazabicyclo-[2,2,2]-octane (DABCO) is distinctly higher than the k DC q value obtained for other noncyclic AlAs. These differences in the k DC q values have been rationalized on the basis of the differences in the orientational restrictions involved in the ET reactions with different types of amines. As understood, n-type donors (AlAs) introduce large orientational restriction and thus significantly reduces the ET efficiency in comparison to the p-type donors (ArAs). Structural constrains are inferred to be the reason for the differences in the k DC q values involving ABCO, DABCO donors in comparison to other noncyclic AlAs. Supportive evidence for the orientational restrictions involving different types of amines donors has also been obtained from DFT based quantum chemical calculations on the molecular orbitals of representative acceptor and donor molecules.
Effect of amino anilines on the fluorescence of coumarin derivative
Journal of Luminescence, 2019
The effect of stereo electronic factors of amino anilines such as orthophenylenediamine (OPD) and para-phenylenediamine (PPD) on the fluorescence of 5,6-benzo-4-azidomethyl coumarin (5BAMC) in polar aprotic and polar protic solvents has been studied. From UV absorption and 1 H NMR studies, observed blue shift in the presence of PPD is due to H-bonding with 5BAMC. Fluorescence quenching studies indicate the role of static and dynamic quenching mechanisms for both the quenchers and larger quenching efficiency of PPD than OPD. The sphere of action static quenching and finite sink approximation models reveal static effect in the excited state and diffusion limited bimolecular quenching reactions. Electrochemical analysis indicates that quenching efficiency of PPD is more than OPD based on the magnitudes of free energy change for electron transfer. Binding equilibria analysis confirms that the magnitude of binding between PPD and 5BAMC is stronger compared to OPD. It is also noticed that the binding between PPD and 5BAMC in polar protic solvents is stronger than that in aprotic solvents. Lastly, from the magnitudes of thermodynamic parameters, interaction between PPD and 5BAMC is hydrophobic and spontaneous. Thus from the present investigation, it is concluded that the separation between two-NH 2 groups in amino anilines plays role in their interaction with coumarin derivative 5BAMC.
Chemical Physics Letters, 2003
Photoinduced intermolecular electron transfer between Rhodamine 3B and N,N-dimethylaniline has been studied in a series of seven liquids: acetonitrile, ethanol, propylene glycol, and mixtures of ethanol, 2-butanol, ethylene glycol, propylene glycol, and glycerol. In each liquid, the donor and acceptors have different diffusion constants and experience distinct dielectric properties. Ps time-dependent fluorescence measurements and steady-state fluorescence yield measurements were made and analyzed using a detailed statistical mechanical theory that includes a distance-dependent Marcus rate constant, diffusion with the hydrodynamic effect, and solvent structure. All solvent-dependent parameters necessary for calculations were measured, including dielectric constants, diffusion constants, and redox potentials, leaving the electronic coupling unknown. Taking the distance-dependence of the coupling to be ϭ1 Å Ϫ1 , data were fit to a single parameter, the coupling matrix element at contact, J 0 . The theory is able to reproduce both the functional form of the time-dependence and the concentration-dependence of the data in all seven liquids by fitting only J 0 . Despite the substantial differences in the properties of the experimental systems studied, fits to the data are very good and the values for J 0 are very similar for all solvents.
International journal of scientific research in computer science, engineering and information technology, 2019
Coumarin derivatives are extensively investigated in terms of their photo physical properties to understand excited state in regard to understand and innovate molecules. In this article we study steady state quenching of fluorescence of a coumarin derivative namely 3-Hydroxy-3-[2-oxo-2-(3-oxo-3H-benzo[f]chromen-2-yl)ethyl]-1,3-dihydro-indol-2-one (3HBCD) in binary mixture of acetonitrile and 1,4 dioxane. Dimethylaniline is used as quencher. A negative deviation is seen with modest quencher concentration in the Stern-Volmer (S-V) plots. The quenching ability of Dimethylaniline in reference to aniline is more due to its higher ionization energies.
Electron transfer in a donor-substituted acridinium dye: evidence for dynamical solvent control
Chemical Physics Letters, 1999
Time-resolved emission is used to explore the intramolecular excited-state electron transfer in a donor-substituted acridinium dye in a variety of solvents at room temperature. Emission decays are predominantly bi-exponential, with the faster of the two time constants being a good measure of the charge transfer time. In 14 high-polarity solvents this time is correlated to the solvation times previously measured with the solvation probe Coumarin 153 via an apparent power law, ² : 0.65 t f 8.4 t. In solvents less polar than acetone the times observed deviate widely from this relationship, probably solv LE ™ CT due to the effects of ion pairing.
Quenching of the excitation energy of coumarin dyes by aniline 1
Canadian Journal of Physics, 2013
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 d ), probability of quenching per encounter (p and p=), and quenching rate parameter (k q and kЈ q ) were experimentally determined in all the solvents. Activation energy of quenching (E a and EЈ a ) was also determined by using the literature values of activation energy of diffusion (E d ). It was found that the values of E a (and EЈ a ) were less than E 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. Résumé : À l'aide des méthodes stationnaire et résolue dans le temps, afin de comprendre le rôle de la diffusion dans le mécanisme d'extinction (de luminescence), nous avons activé dans le toluène les mécanismes d'extinction de colorants coumarine, nommément 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 molécules de soluté ont été excitées par radiation UV de longueur d'onde 360 et 330 nm. Nous avons déterminé expérimentalement, dans tous les solvants, différents paramètres de désactivation, comme la fréquence de collision (k d ), la probabilité de désactivation par collision (p et p=) et le paramètre de taux de désactivation (k q et kЈ q ). Utilisant les valeurs de la littérature pour l'énergie d'activation de la diffusion (E d ), nous avons déterminé les énergies d'activation de désactivation (E a et EЈ a ). Nous trouvons que E a (et EЈ a ) sont plus petites que E d , ce qui indique que les réactions de désactivation sont significativement plus affectées par la diffusion. [Traduit par la Rédaction] ). 1 This manuscript is part of the special issue Mid-and Far-Infrared Spectroscopy: Techniques and Applications published in memoriam of our colleague Arvid Schultz. 976 Can. J. Phys. 91: 976-980 (2013) dx.
The Journal of Physical Chemistry A, 1998
Intermolecular electron transfer (ET), which occurs faster than solvation dynamics, has been investigated using the fluorescence up-conversion technique. The ultrafast ET processes have been observed from the electron-donating solvents to the excited coumarin dyes. In this work we have mainly focused our attention on the roles of the substitution of electron-donating solvent molecules in the ET dynamics. We have used aniline, N-monoalkylanilines, and N,N-dialkylanilines as electron-donating solvents and five 7-amino coumarins as acceptor molecules. For these systems the free energy gaps have been estimated from the cyclic voltammetry measurement and the steady-state absorption and fluorescence measurements. The experimental results indicate that the ET rate depends largely on the substituent groups of the solvent molecules. In N,N-dialkylanilines the ET rate gets smaller as the size of the alkyl substituent group becomes larger. For N-monoalkylanilines, however, the ET dynamics are not changed by the different alkyl substituent groups. In many donor-acceptor combinations we recognized that the ET rate is much faster than the solvation time. We simulated the results by the two-dimensional ET model with solvent and nuclear coordinates and found that the N-alkyl substituent effect on the ET rate appears to be mainly due to the changes in the electronic matrix element. We have also investigated the deuterium isotope effect on the ET dynamics using N-deuterated-N-monoalkylanilines as donor solvents. For the fastest ET the isotope effect is hardly observable, whereas the effect is quite large (∼20%) for slower ET. The deuterium isotope effect seems to mainly come from the change of stabilization energies in intermolecular hydrogen-bonding interaction by deuteration. The extent of deuterium isotope effect on ET is similar for all N-monoalkylanilines used. This result indicates that the size of the alkyl groups does not affect much the hydrogen-bonding interaction. † The Graduate University for Advanced Studies.
Dynamics of intermolecular electron transfer from amines to the excited states of 9-fluorenone
Journal of Photochemistry and Photobiology A: Chemistry, 2013
Dynamics of photoinduced electron transfer (PET) reactions between the singlet (S 1) and the triplet (T 1) excited states of 9-fluorenone or simply fluorenone and a few aromatic and aliphatic amines have been investigated under both diffusive and non-diffusive conditions. Formation of the fluorenone anion radical confirms the electron transfer (ET) from the amines to the excited states of fluorenone. Rate constants for both the forward ET process, k CS , and the charge recombination (CR) process, k CR , have been determined in acetonitrile and benzene solutions. Sub-picosecond time-resolved transient absorption study reveals that quenching of the S 1 state in acetonitrile is biexponential. Lifetime of one of these two components is independent of quencher concentration and its values determined for aniline (7.1 ps), dimethylaniline (8.5 ps) and diethylaniline (6.8 ps) are very similar. It represents the non-diffusive component of the PET reaction. But the lifetime of the other component decreases with increasing quencher concentration and the rate of this diffusive component of the PET reaction nearly agrees with the value determined using steady state fluorescence quenching method. To determine the intrinsic values of the rates of the PET reactions involving the S 1 state of fluorenone, the PET dynamics have been studied in these three neat donor solvents. The forward ET process is biexponential and the lifetimes of these two components are very similar in these solvents and vary in the range 0.3-0.5 ps and 6-8 ps. Nonexponential dynamics of the PET reactions conducted in neat donor-solvents have been discussed using a simple solvent reorientational model.
Photochemistry and Photobiology, 2009
Photophysical studies on coumarin-7 (C7) dye in different protic solvents reveal interesting changes in the properties of the dye on increasing the solvent polarity (Df; Lippert-Mataga solvent polarity parameter) beyond a critical value. Up to Df 0.31,thephotophysicalpropertiesofthedyefollowgoodlinearcorrelationswithDf.ForDf>0.31, the photophysical properties of the dye follow good linear correlations with Df. For Df >0.31,thephotophysicalpropertiesofthedyefollowgoodlinearcorrelationswithDf.ForDf>0.31, however, the photophysical properties, especially the fluorescence quantum yields (F f), fluorescence lifetimes (s f) and nonradiative rate constants (k nr), undergo large deviations from the above linearity, suggesting an unusual enhancement in the nonradiative decay rate for the excited dye in these high polarity protic solvents. The effect of temperature on the s f values of the dye has also been investigated to reveal the mechanistic details of the deexcitation mechanism for the excited dye. Studies have also been carried out in deuterated solvents to understand the role of solute-solvent hydrogen bonding interactions on the photophysical properties of the dye. Observed results suggest that the fluorescence of the dye originates from the planar intramolecular charge transfer (ICT) state in all the solvents studied and the deviations in the properties in high polarity solvents (Df >$0.31) arise due to the participation of a new deexcitation channel associated with the formation of a nonfluorescent twisted intramolecular charge transfer (TICT) state of the dye. Comparing present results with those of a homologous dye coumarin 30 (C30; Photochem. Photobiol., 2004, 80, 104), it is indicated that unlike in C30, the TICT state of the C7 dye does not experience any extra stability in protic solvents compared to that in aprotic solvents. This has been attributed to the presence of intramolecular hydrogen bonding between the NH group (in the 3-benzimidazole substituent) of the C7 dye and its carbonyl group, which renders an extra stability to the planar ICT state, making the TICT state formation relatively difficult. Qualitative potential energy diagrams have been proposed to rationalize the differences observed in the results with C7 and C30 dyes in high polarity protic solvents.
Photoinduced electron transfer from dimethyl aniline to coumarin dyes in reverse micelles
2005
Photoinduced electron transfer between different coumarin dyes and N, N-dimethyl aniline has been investigated in AOT reverse micelle using steady state and time resolved fluorescence spectroscopy. We have observed a slower electron transfer rate in reverse micelle in comparison to that in the neat solvent. Moreover, we have observed retardation in the electron transfer rate in the correlation of the free energy change with the electron transfer rate.