Photoinduced electron transfer from dimethyl aniline to coumarin dyes in reverse micelles (original) (raw)
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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.
Photophysical features of coumarin 120 in reverse micelles
Journal of Molecular Structure, 2018
The photophysical properties of 7-amino 4-methyl coumarin (C120) were investigated in the reverse micelle systems by using molecular UV-Vis absorption, steady-state and timeresolved fluorescence spectroscopy techniques. For this purpose, the fluorescence spectra of C120 dye in reverse micelle systems with different values of W 0 (from 0 to 45) were examined. The bathochromic shift from 400 nm to 439 nm was observed for the fluorescence maxima of C120. It was found that intramolecular arrangements occurred in the structure of C120 molecule due to specific solute-solvent interactions. Fluorescence lifetime measurements were carried out and quantum yield values, radiative (k r) and non-radiative rate constants (k nr) were calculated. The data compared with the values reported in the literature. Steady-state anisotropy (r) studies were done to explain the microenvironment around the C120 molecules. Anisotropy data varying 0.048 to 0.030 with varying W 0 displayed that the microenvironment for the C120 dye in water pools of reverse micelles was different than C120 dye in pure water which is 0.009. The microviscosity and rotational relaxation time values were calculated as a function of W 0. We have determined that C120 dye is a useful probe for the definition the microviscosity of reverse micelles with different water pool sizes.
The Journal of Physical Chemistry A, 2000
Electron transfer (ET) from aniline, N-alkylanilines, N,N-dialkylanilines, and o-phenylenediamine to a number of excited (S 1) 4-CF 3-coumarin dyes having differently substituted 7-amino groups have been investigated in acetonitrile solutions using steady-state (SS) and time-resolved (TR) fluorescence quenching measurements. Direct evidence for the ET reactions in the present systems have been obtained by characterizing the amine cation radicals using picosecond transient absorption measurements in the visible region. The experimentally determined bimolecular quenching constants (k q) are seen to correlate nicely with the free energy changes (∆G°) for the ET reactions, within the framework of the Marcus ET theory. The total reorganization energy (λ) estimated from such correlation indicates that the solvent reorganization (λ s) plays the major role in governing the ET dynamics in the present systems. A comparison of the present results under diffusive conditions with those reported earlier under nondiffusive conditions indicates that the ET dynamics in the latter cases are much faster than in the former. The results are discussed considering a structural difference between the encounter complexes formed under diffusive and nondiffusive conditions.
Photoinduced electron transfer in the head group region of sodium dodecyl sulfate micelles
Journal of Luminescence, 2005
Photoinduced electron transfer between octadecylrhodamine B (a hole donor) and N, N-dimethyl-1-napthylamine (hole acceptor), located in the head group region of sodium dodecylsulfonate micelles, has been examined for different acceptor concentrations using time resolved fluorescence. The experimental results were analyzed using the Marcus distance-dependent transfer rate modified to take into account the heterogeneous nature of the micelles. Diffusion of the donor/acceptors is included in the theoretical analysis. The results are compared with earlier experiments involving the same donor-acceptor combination but in a different type of micelle.
Langmuir, 2008
6-Propionyl-2-(N,N-dimethyl)aminonaphtahalene, PRODAN, is widely used as a fluorescent molecular probe due to its significant Stokes shift in polar solvents. It is an aromatic compound with intramolecular charge-transfer (ICT) states which can be particularly useful as sensors. In this work, we performed absorption, steady-state, time-resolved fluorescence (TRES), and time-resolved area normalized emission (TRANES) spectroscopies on PRODAN dissolved in nonaqueous reverse micelles. The reverse micelles are composed of polar solvents/sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT)/n-heptane. Sequestered polar solvents included ethylene glycol (EG), propylene glycol (PG), glycerol (GY), formamide (FA), dimethylformamide (DMF), and dimethylacetamide (DMA). The experiments were performed with varying surfactant concentrations at a fixed molar ratio W S ) [polar solvent]/[AOT]. In every reverse micelle studied, the results show that PRODAN undergoes a partition process between the external solvent and the reverse micelle interface. The partition constants, K p , are quantified from the changes in the PRODAN emission and/or absorption spectra with the surfactant concentration. The K p values depend strongly on the encapsulated polar solvent and correlate quite well with the AOT reverse micelle interface's zones where PRODAN can exist and emits. Thus, the partition toward the reverse micelle interface is strongly favored in DMF and DMA containing micelles where the PRODAN emission comes only from an ICT state. For GY/AOT reverse micelles, the K p value is the lowest and only emission from the local excited (LE) state is observed. On the other hand, for EG/AOT, PG/AOT, and water/AOT reverse micelles, the K p values are practically the same and emission from both states (LE and ICT) is simultaneously detected. We show here that it is possible to control the PRODAN state emission by simply changing the properties of the AOT reverse micelle interfaces by choosing the appropriate polar solvent to make the reverse micelle media. Indeed, we present experimental evidence with the answer to the long time question about from which state does PRODAN emit, a process that can be controlled using the unique reverse micelle interfaces properties.
Journal of Physical Chemistry A, 2006
Photoinduced electron transfer (PET) from N,N-dimethylaniline (DMA) to four coumarin dyes (C151, C481, C153, and C480) inside the cavity of hydroxypropyl γ-cyclodextrin (hpCD) is studied using femtosecond upconversion. The rate of PET is found to be nonexponential and to vary significantly with the coumarin dyes. The rate for C481 is 100 times faster than that for C480. The PET rate displays a bell-shaped dependence on the free energy change and thus reveals a Marcus-type inverted region. The anisotropy decay of the four dyes in hpCD are found to be very similar, and hence the observed variation in the rate of PET is not due to variation in rotational diffusion of the acceptors (coumarin dyes).
Chemical Physics Letters, 2005
The energy transfer using 7-amino coumarin dyes as donor and rhodamine 590 (Rh6G) as acceptor were investigated in methanol and acetonitrile solubilized non-aqueous reverse micelles using steady state and time resolved fluorescence spectroscopy. For all donors and acceptor we have obtained higher value of overlap integral (J(k)) and higher value of Fö rster distance (R 0 ). Although we have got higher value of J(k) but the rate constant of energy transfer (k ET ) in almost all systems are small. Coumarin153-Rh6G pair is the most efficient donor acceptor pair as reflected by the value of k ET . The different value of energy transfer rate constant in case of different donors indicate the dependence of energy transfer on the structure of donors.
Intramolecular Charge Transfer Processes in Confined Systems. Nile Red in Reverse Micelles†
The Journal of Physical Chemistry B, 1997
Intramolecular charge transfer (ICT) processes of the neutral fluorescence probe, nile red, I, confined in the water pool of aerosol-OT (AOT) reverse micelle in n-heptane, is studied using picosecond emission spectroscopy. Utilizing the solvatochromism of nile red, only those probe molecules inside the reverse micelle are selectively excited. It is observed that while in aqueous solutions the lifetime (τ f) of nile red is 650 ps, inside the reverse micelles τ f increases to 3.73 ns in reverse micelle and to 2.06 ns at the highest water content of the microemulsion (w o) 32). With increase in the water-to-surfactant ratio, w o , as the water pool swells in size, the lifetime and quantum yield of emission decrease and the rate of the ICT process of nile red increases. However, the magnitude of the change (at most 8 times) in the rate of the ICT process of nile red compared to that of ordinary water is much smaller than the several thousandfold decrease observed in the solvation dynamics of water in the water pool relative to bulk water. It is proposed that while the solvation dynamics in the water pool is governed by the dielectric relaxation time, dynamics of the ICT process is controlled by the static polarity of the medium.