Stopped-Flow Studies of the Formation of Organic Nanocrystals in the Reprecipitation Method

Oliveira, Daniel; Baba, Koichi; Teizer, W.; Kasai, Hitoshi; Oikawa, Hidetoshi; Nakanishi, Hachiro

doi:10.5772/17303

Cited by 5 publications

(7 citation statements)

References 43 publications

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“…First, there appears to be a very weak, broad absorption peak in the flocculated suspension around 358 nm, just ahead of the primary absorption peaks. This absorbance could be indicative of pyrene associating with the asphaltene agglomerates in solution, as aggregation of polyaromatics tends to cause a red-shift in absorbance and fluorescence . A similar comparison of the fluoranthene-doped mixtures could not detect any shifts in the fluoranthene spectrum (data not shown), which may indicate a weaker interaction with asphaltenes under these conditions compared to pyrene.…”

Section: Results and Discussionmentioning

confidence: 86%

Fused Aromatics To Restore Molecular Packing of Aged Bituminous Materials

Pahlavan

Hosseinnezhad

Samieadel

et al. 2019

Ind. Eng. Chem. Res.

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This study incorporates computational and laboratory experiments to determine specific interaction mechanisms between conjugated structures (interrupted and continuous conjugates) and selected polyaromatics hydrocarbons (PAH) stacks such as those found in oxidized asphaltene molecules. The theoretical results obtained by quantum-mechanical calculations and molecular dynamics simulations show that both continuous and interrupted conjugates are effective to weaken the π-intersheet forces and decrease the size of PAH nanoaggregates, with interrupted conjugates being more efficient than continuous conjugates to exfoliate PAH stacks. Owing to their limited partial entrance into the PAH stacks, interrupted conjugates are not trapped inside the PAH interlayer, and can easily detach from the stacks. This allows an interrupted conjugate not to be consumed in interaction with one PAH stack, making the interrupted conjugate available to affect many other stacks in the matrix. The higher exfoliation capacity of the interrupted aromatic conjugates is also evidenced in the results of our experiments based on UV−vis and rheometry analyses. This is reflected in a higher reduction in the polydispersity index and a higher increase in both the crossover frequency and crossover modulus of aged bitumen (containing stacks of large PAH referred to as asphaltene nanoaggregates) when it is doped with an interrupted conjugate (fluoranthene) compared to when it is doped with a continuous conjugate (pyrene). The study results contribute to the body of knowledge by providing an in-depth understanding of how variation in the π-electron distribution of conjugated structures affects their efficacy to exfoliated self-assembled stacked structures of polyaromatic hydrocarbons such as asphaltenes.

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Section: Results and Discussionmentioning

confidence: 86%

Fused Aromatics To Restore Molecular Packing of Aged Bituminous Materials

Pahlavan

Hosseinnezhad

Samieadel

et al. 2019

Ind. Eng. Chem. Res.

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“…Excited singlet state of anthracene molecule (see Scheme for the molecular structure) emits in the blue region (i.e., in the 370–480 nm region) in solution phase. However, in nanoparticle form, the entire emission band is red-shifted by about 20 nm, and the singlet anthracene exciton emits in the blue-violet region. ,, Easy synthesis route and possibilities of generation of multiple colors with better emission yields through doping in nanoaggregates motivated us to take up the present work. However, while the emission yield of anthracene in solution phase is around 0.36, it reduces to 0.17 ± 0.02 in the case of nanoaggregates. − …”

Section: Introductionmentioning

confidence: 99%

Ultrafast Energy Transfer Process in Doped-Anthracene Nanoaggregates is Controlled by Exciton Diffusion: Multiple Doping Leads to Efficient White Light Emission

2016

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Quite similar structures of polycyclic aromatic hydrocarbons make them suitable for doping of one molecule into the crystalline structure or aggregate of another and tuning of the optical properties of the composite system. Anthracene nanoaggregates, singly or multiply doped with perylene, tetracene, and pentacene, have been synthesized using reprecipitation technique. Following photoexcitation of anthracene molecule in the nanoaggregate, anthracene exciton transfers energy to the dopant molecule(s). Energy transfer (ET) efficiency of about 98% could be achieved with the concentration of about 6 × 10 −3 mol dm −3 for perylene or tetracene as the acceptor and about 92% efficiency with the doping concentration of about 5 × 10 −2 mol dm −3 for pentacene as the acceptor. Very fast energy transfer rates (∼3−6 × 10 11 dm 3 mol −1 s −1 ) observed here could not be explained by invoking Forster's energy transfer mechanism. However, the rate of diffusion of anthracene exciton determined experimentally using exciton−exciton annihilation reaction in the anthracene nanoaggregate matrix has been shown to agree well with the ET rate. This observation leads us to conclude that the ET rate in the nanoaggregate matrix is controlled by exciton diffusion. Using those three dopants with proper concentration ratios, efficient white light emission has been achieved following optical excitation of the nanoaggregate sample at the absorption band of the anthracene molecule.

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“…Various methods, for example, vapor deposition, colloidal chemical reaction, reprecipitation, and so forth, have been reported for the synthesis of organic nanoaggregates. ,− Here, we have used the reprecipitation method because of its simplicity and facileness for syntheses of nanoaggregates . We have used DMSO as the good solubility solvent and water as the poor solubility solvent.…”

Section: Methodsmentioning

confidence: 99%

“…58,105−108 Here, we have used the reprecipitation method because of its simplicity and facileness for syntheses of nanoaggregates. 108 We have used DMSO as the good solubility solvent and water as the poor solubility solvent. In our efforts to prepare the particles of smaller diameter and narrow size dispersity, we tried several solvents including acetonitrile and tetrahydrofuran as the good solubility solvent.…”

Section: Methodsmentioning

confidence: 99%

Exciton Dynamics in Pyrene and Perylene Nanoaggregates

Manna

Palit

2020

J. Phys. Chem. C

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Photophysical and diffusion properties of excitons generated in perylene and pyrene nanoaggregates have been investigated using steady state as well as time-resolved absorption and emission spectroscopic techniques. The average sizes and heights of the nanoaggregates prepared by the reprecipitation method have been estimated as 120 ± 20 and 60 ± 10 nm, respectively. X-ray diffraction spectra reveal that molecular packing in these nanoaggregates is very similar to that in the α-form (face-to-face pair or dimeric structure) of the crystals, but with possibilities of a large number of disordered regions consisting of monomer molecules. Therefore, following photoexcitation of nanoaggregates, both monomeric and dimeric exciton states are populated. This work, for the first time, could reveal the dynamics of interactions between these two kinds of exciton states, because of which the photophysical and diffusion properties of the excitons are significantly different from those in single crystals. Population yield of the dimeric self-trapped exciton or E state, which is the lowest energy exciton state, is negligibly small via self-trapping of dimeric excitons (dimeric channel) in the <200 ps time domain because of efficient energy transfer from dimeric excitons to monomers. However, the monomeric excitons, which are populated either independently through direct photoexcitation or by energy transfer from the dimeric excitons, contribute to an additional (monomeric) channel populating the E state via energy transfer processes occurring in the nanosecond (ns) time domain. Diffusion coefficients and diffusion lengths of the monomeric excitons estimated in both these nanoaggregates are comparable to those in the β-form of the crystals but much larger than those values reported for the α-form and hence ensure a better or comparable efficiency of energy migration in nanoaggregates as compared to that of single crystals.

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Stopped-Flow Studies of the Formation of Organic Nanocrystals in the Reprecipitation Method

Cited by 5 publications

References 43 publications

Fused Aromatics To Restore Molecular Packing of Aged Bituminous Materials

Fused Aromatics To Restore Molecular Packing of Aged Bituminous Materials

Ultrafast Energy Transfer Process in Doped-Anthracene Nanoaggregates is Controlled by Exciton Diffusion: Multiple Doping Leads to Efficient White Light Emission

Exciton Dynamics in Pyrene and Perylene Nanoaggregates

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