Ultrafast conformation equilibration in triphenyl methane dyes analyzed by time resolved induced photoabsorption

Mokhtari, Arash; Fini, Lorenzo; Chesnoy, J.

doi:10.1063/1.452987

Cited by 55 publications

(60 citation statements)

References 27 publications

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“…The isomerization dynamics were best characterized by a single exponential decay (2.0 + 0.3 ps at the air/aqueous interface). These rates are significantly slower than the dominant decay component of ~ 0.7 ps reported for malachite green in bulk water [49][50][51].…”

Section: Resultsmentioning

confidence: 71%

Ultrafast dynamics and structure at aqueous interfaces by second harmonic generation

et al. 1996

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Femtosecond time-resolved second harmonic generation studies of the barrierless isomerization of an organic dye, malachite green (MG), have been carded out at several aqueous interfaces. A comparison of the dynamics at the air/aqueous, alkane/aqueous and silica/aqueous interfaces, indicates increased friction and increased water structure at the aqueous interfaces relative to bulk water, in support of molecular simulations, with the silica/aqueous interface being the most structured. The dynamics are slower at all of these interfaces than in bulk water, by a factor of three to five in the case of the air/aqueous and alkane/aqueous interfaces, and almost an order of magnitude in the case of the silica/aqueous interface. These investigations also indicate that the generally accepted isomerization model of twisting of the three aromatic rings about the central carbon atom requires modification in that the synchronous twisting of all three aromatic rings is not necessary for rapid internal conversion from the excited to ground electronic state. In contrast to MG, the dynamics of the activated photoisomerization of the cyanine dye, 3,3'-diethyloxadicarbocyanine iodide (DODCI), is faster at the air/aqueous interface than in bulk aqueous solution. The different dynamics of MG and DODCI suggest that the interface friction must be described in terms of the orientation and solvent structure in the vicinity of the chromophores involved in the isomerization process.

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Section: Resultsmentioning

confidence: 71%

Ultrafast dynamics and structure at aqueous interfaces by second harmonic generation

et al. 1996

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“…The decay times obtained with MG agree very well with earlier findings. 24,31,33 The data reported for BG are scarce and refer only to single-color pump-probe experiments carried out at 635 nm 33 with a temporal resolution of approximately 30 fs. The authors have found two time constants shorter than 250 fs as well as three longer values: 0.55, 0.69, and 2.7 ps.…”

Section: Resultsmentioning

confidence: 99%

“…For this reason MG has been the subject of numerous stationary and time-resolved spectroscopic experiments that aimed to describe its deactivation pathway. [28][29][30][31][32][33][34][35] It is generally agreed that the relaxation is intrinsically barrierless and involves rotation of the aniline or phenyl substituents. The friction exerted by the environment on the rotating rings accounts for the viscosity dependence of the excited state lifetime.…”

Section: Introductionmentioning

confidence: 99%

Local Viscosity of Binary Water+Glycerol Mixtures at Liquid/Liquid Interfaces Probed by Time-Resolved Surface Second Harmonic Generation

2009

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The excited-state relaxation of malachite green and brilliant green in solvents of various viscosity has been investigated at liquid/liquid interfaces and in bulk solutions by surface second harmonic generation and transient absorption spectroscopy. Mixtures of water and glycerol in various proportions have been used as solvents of variable viscosity. Transient absorption measurements in bulk revealed that both dyes are suitable as a probe of local viscosity for water+glycerol mixtures and that two of three processes following the optical excitation exhibit the same power dependence on solvent viscosity. This observation leads to assignment of the processes to a twist and twist-back of the aromatic rings attached to the central carbon atom of the dye. Therefore, identification of the intermediate state observed in the radiationless deactivation pathway with the twisted form of the dye has been supported. The time profiles of the second harmonic signal recorded at water+glycerol/ dodecane interfaces have been found to be monoexponential at low dye concentrations (below 10 -5 M) and biexponential at higher concentrations, and therefore the origin of the slower component has been attributed to the relaxation of dye aggregates adsorbed at the interface. The decay times measured at interfaces increased with increasing amount of glycerol in the mixture, but the rise was slower than in bulk solution. Therefore, the viscosity at the interfacial region, higher than that of the bulk solution, is mainly determined by structural modification of the solvent resulting from interactions between the two liquids that constitute the interface and addition of glycerol affects viscosity, only to a lesser extent. We have also shown that if the viscosity of the upper layer is much higher (at least 1 order of magnitude) than that of water or short alkanes, a slowdown of the relaxation is observed. This contradicts earlier findings and means that large amplitude motion of all three rings is involved in the deactivation of the excited molecule, but the rotation of the phenyl ring, which is smaller than the alkyl-substituted aniline groups, becomes a bottleneck for the relaxation in very viscous environments.

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“…According to the literature, this process is slightly solvent dependent and involves torsional re-equilibration of the excited state. 33,35 The shortest time constant found here, τ b1 , can be associated with this relaxation step. This process is followed by a nonradiative transition to an intermediate state S x .…”

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confidence: 99%

“…[31][32][33][34][35][36][37] Excitation of MG in the S 0 -S 1 transition is followed by ultrafast relaxation from the Franck-Condon S 1 state to equilibrium. According to the literature, this process is slightly solvent dependent and involves torsional re-equilibration of the excited state.…”

mentioning

confidence: 99%

Effect of Salt on the Excited-State Dynamics of Malachite Green in Bulk Aqueous Solutions and at Air/Water Interfaces: a Femtosecond Transient Absorption and Surface Second Harmonic Generation Study

et al. 2009

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The ultrafast excited-state dynamics of Malachite Green (MG) in bulk aqueous solutions and at air/water interfaces, in particular the effect of the presence of various sodium salts in the aqueous phase, has been investigated by transient absorption and surface second harmonic generation. In bulk solutions, a slowing down of the ground-state recovery that can be unambiguously ascribed to the formation of aggregates of various sizes is observed at high (>0.3 M) salt concentrations only, with the exception of NaSCN where an effect is already found at 0.05 M. At the interface, small amounts of salt result in two effects: 1) an increase of the stationary surface second harmonic signal and 2) a slowing down of the ground-state recovery of MG. These phenomena are explained by the formation of aggregates due to an increase of the interfacial MG concentration upon addition of salt. The dependencies of both effects on salt concentration are correlated and vary with the anion as SCNThis order is almost the opposite as that in the Hofmeister series for the salting-out strength.

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Ultrafast conformation equilibration in triphenyl methane dyes analyzed by time resolved induced photoabsorption

Cited by 55 publications

References 27 publications

Ultrafast dynamics and structure at aqueous interfaces by second harmonic generation

Ultrafast dynamics and structure at aqueous interfaces by second harmonic generation

Local Viscosity of Binary Water+Glycerol Mixtures at Liquid/Liquid Interfaces Probed by Time-Resolved Surface Second Harmonic Generation

Effect of Salt on the Excited-State Dynamics of Malachite Green in Bulk Aqueous Solutions and at Air/Water Interfaces: a Femtosecond Transient Absorption and Surface Second Harmonic Generation Study

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