The excited-state relaxation dynamics of D149, one of the metal-free substituted indoline dyes used in dye-sensitized solar cells, is studied in the whole composition range of the 1butyl-3-methylimidazolium tetrafluoroborate (BmimBF 4 )−acetonitrile binary mixture by using time-integrated absorption, emission, and time-resolved transient absorption (TA) spectroscopies. The comparative analysis of absorption and emission spectra indicates that the value of Stokes shift reduces monotonically with decreasing mixture polarity. The global analysis of timeresolved TA spectra indicates the presence of four different time components related to different processes in the excited state of the dye. Importantly, the observed timescales are highly sensitive to composition, polarity, and viscosity of the binary mixture. Increase of viscosity and decrease of polarity observed for increasing ionic liquid (IL) content in the mixture lead to overall increase in the emission lifetime (S 1 −S 0 ) of D149. At a lower IL mole fraction (X IL = 0.1), the emission lifetime shows a minimum that can be traced back to the change from the situation in which the local environment of the dye is dominated by the interactions in acetonitrile to that in which it is dominated by those in BmimBF 4 . This also is reflected in the occurrence of a minimum in relative quantum yield in the same range of X IL . The origin of the other moderately long-time component (33 ps in ACN-120 ps in BmimBF 4 ) is still debatable; however, for pure IL and all the mixtures, the composition dependence of this timescale is similar to that of the longest emission lifetime.
The inhomogeneity distribution in four imidazolium-based ionic liquids (ILs) containing the 1-butyl-3-methylimidazolium (C 4 mim) cation, coupled with tetrafluoroborate (BF 4 ), hexafluorophosphate (PF 6 ), bis(trifluoromethanesulfonyl)amide (TFSA), and trifluoromethanesulfonate (TfO) anions, was characterized using Voronoi polyhedra. For this purpose, molecular dynamic simulations have been performed on the isothermal−isobaric (NpT) ensemble. We checked the ability of the potential models to reproduce the experimental density, heat of vaporization, and transport properties (diffusion and viscosity) of these ionic liquids. The inhomogeneity distribution of ions around the ring, methyl, and butyl chain terminal hydrogen atoms of the C 4 mim cation was investigated by means of Voronoi polyhedra analysis. For this purpose, the position of the C 4 mim cation was described successively by the ring, methyl, and butyl chain terminal hydrogen atoms, while that of the anions was described by their F or O atom. We calculated the Voronoi polyhedra distributions of the volume, the density, and the asphericity parameters as well as that of the radius of the spherical intermolecular voids. We carried out the analysis in two steps. In the first step, both ions were taken into account. The calculated distributions gave information on the neighboring ions around a reference one. In the second step, to distinguish between like and oppositely charged ions and then to get information on the inhomogeneity distribution of the like ions, we repeated the same calculations on the same sample configurations and removed one of the ions and considered only the other one. Detailed analysis of these distributions has revealed that the ring hydrogen atoms are mainly solvated by the anions, while the methyl and butyl terminal H atoms are surrounded by like atoms. The extent of this inhomogeneity was assessed by calculating the cluster size distribution that shows that the dimers are the most abundant ones.
We have performed the measurements of the optical Kerr effect signal time evolution up to 4 ns for a mixture of 1-alkyl-3-methyl-imidazolium hexafluorophosphate (BMIM PF6 ) ionic liquid and acetonitrile...
Magnetic ionic liquids (MILs), which incorporate paramagnetic ions, promise to minimize manual user intervention, decrease extraction times, and facilitate rapid recovery of the analyte-enriched extraction solvent. If, however, fluorescence is employed in the downstream analysis of an analyte tagged with a fluorophore, the paramagnetic ion may quench fluorescence by introducing new nonradiative processes. Thus, it is necessary to employ a paramagnetic ion that offers a compromise between possessing a high magnetic moment and not introducing new nonradiative channels. Mn(II), Fe(III), Co(II), and Ni(II) are considered in combination with phosphonium cations and anionic ligands based upon halides or hexafluoroacetylacetonate. Among the possibilities examined, MILs containing Mn(II) provide the best alternative for a model system involving DNA.
Light-induced
charge accumulation is at the heart of
biomimetic
systems aiming at solar fuel production in the realm of artificial
photosynthesis. Understanding the mechanisms upon which these processes
operate is a necessary condition to drive down the rational catalyst
design road. We have built a nanosecond pump–pump–probe
resonance Raman setup to witness the sequential charge accumulation
process while probing vibrational features of different charge-separated
states. By employing a reversible model system featuring methyl viologen
(MV) as a dual electron acceptor, we have been able to watch the photosensitized
production of its neutral form, MV0, resulting from two
sequential electron transfer reactions. We have found that, upon double
excitation, a fingerprint vibrational mode corresponding to the doubly
reduced species appears at 992 cm–1 and peaks at
30 μs after the second excitation. This has been further confirmed
by simulated resonance Raman spectra which fully support our experimental
findings in this unprecedented buildup of charge seen by a resonance
Raman probe.
It has been recognized that the understanding of the photo physic of the dyes used in solar cells in an important step in improving their efficiency. Certainly using ionic liquid as an electrolyte is a good solution as it stabilizes the excited state of the dye, however, because of the high viscosity, the diffusion of the components of the solar cell (dye, electrolyte, the chosen redox couple) is very low and has consequences on the other processes (Forward and backward processes). One of the ideas, is to modulate the viscosity of the ionic liquid by mixing the ionic liquid with a solvent. The goal then of this work is to quantify the mixture composition dependence of the excited state relaxation times. Other studies should be carried out to quantify the mixture dependence on the time characteristics of other processes (charge injection, collection etc.) to optimize the working optimal conditions of the solar cell. Following this goal, the present study is devoted to characterize the relaxation time of in the whole mixture composition of BmimBF4 and acetonitrile and in the neat components. For the first time, the decay relaxation times of the first excited electronic state of D149 dye, as obtained by transient absorption spectroscopy (TAS). These relaxation times are monitored by a gradual change of the local structure around a dye, from the one dominated by the interionic interactions, high viscosity and low polarity (as quantified by the static dielectric constant) in BmimBF4 to the one that is dominated by dipole-dipole interactions, low viscosity and high polarity in acetonitrile.<br>
It has been recognized that the understanding of the photo physic of the dyes used in solar cells in an important step in improving their efficiency. Certainly using ionic liquid as an electrolyte is a good solution as it stabilizes the excited state of the dye, however, because of the high viscosity, the diffusion of the components of the solar cell (dye, electrolyte, the chosen redox couple) is very low and has consequences on the other processes (Forward and backward processes). One of the ideas, is to modulate the viscosity of the ionic liquid by mixing the ionic liquid with a solvent. The goal then of this work is to quantify the mixture composition dependence of the excited state relaxation times. Other studies should be carried out to quantify the mixture dependence on the time characteristics of other processes (charge injection, collection etc.) to optimize the working optimal conditions of the solar cell. Following this goal, the present study is devoted to characterize the relaxation time of in the whole mixture composition of BmimBF4 and acetonitrile and in the neat components. For the first time, the decay relaxation times of the first excited electronic state of D149 dye, as obtained by transient absorption spectroscopy (TAS). These relaxation times are monitored by a gradual change of the local structure around a dye, from the one dominated by the interionic interactions, high viscosity and low polarity (as quantified by the static dielectric constant) in BmimBF4 to the one that is dominated by dipole-dipole interactions, low viscosity and high polarity in acetonitrile.<br>
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