Jiyun Hong - Academia.edu (original) (raw)

Papers by Jiyun Hong

Research paper thumbnail of Excited-State Bond Contraction and Charge Migration in a Platinum Dimer Complex Characterized by Xray and Optical Transient Absorption Spectroscopy

Research paper thumbnail of A Theory-guided X-ray Absorption Spectroscopy Approach for Identifying Active Sites in Atomically Dispersed Transition Metal Catalysts

Atomically dispersed supported metal catalysts offer new properties and the benefits of maximized... more Atomically dispersed supported metal catalysts offer new properties and the benefits of maximized metal accessibility and utilization. The characterization of these materials, however, remains challenging. Using atomically-dispersed Pt supported on crystalline MgO (chosen for its well-defined bonding sites for Pt) as a prototypical example, in this work, we demonstrate how systematic density functional theory calculations (for assessing all the potentially stable Pt sites) combined with automated EXAFS analysis can lead to unbiased identification of isolated, surface-enveloped platinum cations as the catalytic species for CO oxidation. The catalyst has been characterized by atomic-resolution imaging, EXAFS, and HERFD-XANES spectroscopies; the proposed Pt site are in full agreement with experiment. This theory-guided workflow leads to rigorously determined structural models and provides a more detailed picture of the structure of the catalytically active sites than what is currently ...

Research paper thumbnail of Identifying Higher Oxygenate Synthesis Sites in Cu Catalysts Promoted and Stabilized by Atomic Layer Deposited Fe2O3

Research paper thumbnail of Understanding Support Effects of ZnO‐Promoted Co Catalysts for Syngas Conversion to Alcohols Using Atomic Layer Deposition

Research paper thumbnail of Reduction and Agglomeration of Supported Metal Clusters Induced by High-Flux X-ray Absorption Spectroscopy Measurements

The Journal of Physical Chemistry C

Research paper thumbnail of Reducing instability in dispersed powder photocatalysis derived from variable dispersion, metallic co-catalyst morphology, and light fluctuations

Journal of Photochemistry and Photobiology

Research paper thumbnail of The Consortium for Operando and Advanced Catalyst Characterization via Electronic Spectroscopy and Structure (Co-ACCESS) at Stanford Synchrotron Radiation Lightsource (SSRL)

Synchrotron Radiation News

Research paper thumbnail of X-ray Snapshots Reveal Conformational Influence on Active Site Ligation During Metalloprotein Folding

Chemical Science

Cytochrome c (cyt c) has long been utilized as a model system to study metalloprotein folding dyn... more Cytochrome c (cyt c) has long been utilized as a model system to study metalloprotein folding dynamics and the interplay between active site ligation and tertiary structure. However, recent reports...

Research paper thumbnail of Revealing Fast Structural Dynamics in pH-Responsive Peptides with Time-Resolved X-ray Scattering

The Journal of Physical Chemistry B

Research paper thumbnail of Investigation of the photoinduced axial ligation process in the excited state of nickel(II) phthalocyanine

Journal of Photochemistry and Photobiology A: Chemistry

Research paper thumbnail of {"__content__"=>"The Nature of the Long-Lived Excited State in a Ni Phthalocyanine Complex Investigated by X-Ray Transient Absorption Spectroscopy.", "sup"=>{"__content__"=>"II"}}

ChemSusChem, Jan 31, 2018

The nature of the photoexcited state of octabutoxy nickel(II) phthalocyanine (NiPcOBu ) with a 50... more The nature of the photoexcited state of octabutoxy nickel(II) phthalocyanine (NiPcOBu ) with a 500 ps lifetime was investigated by X-ray transient absorption (XTA) spectroscopy. Previous optical, vibrational, and computational studies have suggested that this photoexcited state has a ligand-to-metal charge transfer (LMCT) nature. By using XTA, which provides unambiguous information on the local electronic and nuclear configuration around the Ni center, the nature of the excited state of NiPcOBu was reassessed. Using X-ray probe pulses from a synchrotron source, the ground- and excited-state X-ray absorption spectra of NiPcOBu were measured. Based on the results, we identified that the excited state exhibits spectral features that are characteristic of a Ni (3dz2 ,3dx2-y2 ) state rather than a LMCT state with a transiently reduced Ni center. This state resembles the (d,d) state of nickel(II) tetramesitylphorphyrin. The XTA features are rationalized based on the inherent cavity sizes ...

Research paper thumbnail of Insulin hexamer dissociation dynamics revealed by photoinduced T-jumps and time-resolved X-ray solution scattering

Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, Jan 11, 2018

The structural dynamics of insulin hexamer dissociation were studied by the photoinduced temperat... more The structural dynamics of insulin hexamer dissociation were studied by the photoinduced temperature jump technique and monitored by time-resolved X-ray scattering. The process of hexamer dissociation was found to involve several transient intermediates, including an expanded hexamer and an unstable tetramer. Our findings provide insights into the mechanisms of protien-protein association.

Research paper thumbnail of Probing Cytochrome c Folding Transitions upon Phototriggered Environmental Perturbations Using Time-Resolved X-ray Scattering

The journal of physical chemistry. B, Jan 15, 2018

Direct tracking of protein structural dynamics during folding-unfolding processes is important fo... more Direct tracking of protein structural dynamics during folding-unfolding processes is important for understanding the roles of hierarchic structural factors in the formation of functional proteins. Using cytochrome c (cyt c) as a platform, we investigated its structural dynamics during folding processes triggered by local environmental changes (i.e., pH or heme iron center oxidation/spin/ligation states) with time-resolved X-ray solution scattering measurements. Starting from partially unfolded cyt c, a sudden pH drop initiated by light excitation of a photoacid caused a structural contraction in microseconds, followed by active site restructuring and unfolding in milliseconds. In contrast, the reduction of iron in the heme via photoinduced electron transfer did not affect conformational stability at short timescales (<1 ms), despite active site coordination geometry changes. These results demonstrate how different environmental perturbations can change the nature of interaction b...

Research paper thumbnail of Electronic and nuclear contributions to time-resolved optical and X-ray absorption spectra of hematite and insights into photoelectrochemical performance

Energy Environ. Sci.

Spectra show both transient photocarriers and lattice heating.

Research paper thumbnail of Direct Observation of Insulin Association Dynamics with Time-Resolved X-ray Scattering

The Journal of Physical Chemistry Letters

Biological functions frequently require protein-protein interactions that involve secondary and t... more Biological functions frequently require protein-protein interactions that involve secondary and tertiary structural perturbation. Here we study protein-protein dissociation and reassociation dynamics in insulin, a model system for protein oligomerization. Insulin dimer dissociation into monomers was induced by a nanosecond temperature-jump (T-jump) of ∼8 °C in aqueous solution, and the resulting protein and solvent dynamics were tracked by time-resolved X-ray solution scattering (TRXSS) on time scales of 10 ns to 100 ms. The protein scattering signals revealed the formation of five distinguishable transient species during the association process that deviate from simple two-state kinetics. Our results show that the combination of T-jump pump coupled to TRXSS probe allows for direct tracking of structural dynamics in nonphotoactive proteins.

Research paper thumbnail of Solution Structures of Highly Active Molecular Ir Water-Oxidation Catalysts from Density Functional Theory Combined with High-Energy X-Ray Scattering and EXAFS Spectroscopy

Journal of the American Chemical Society, May 18, 2016

The solution structures of highly active Ir water-oxidation catalysts are elucidated by combining... more The solution structures of highly active Ir water-oxidation catalysts are elucidated by combining density functional theory, high-energy X-ray scattering (HEXS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. We find that the catalysts are Ir dimers with mono-μ-oxo cores and terminal anionic ligands, generated in situ through par-tial oxidation of a common catalyst precursor. The pro-posed structures are supported by 1H and 17O NMR, EPR, resonance Raman and UV-visible spectra, electrophoresis, etc. Our findings are particularly valuable to understand the mechanism of water oxidation by highly reactive Ir catalysts. Importantly, our DFT-EXAFS-HEXS methodology provides a new in-situ technique for characterization of active species in catalytic systems.

Research paper thumbnail of Synthesis, structure, ultrafast kinetics, and light-induced dynamics of CuHETPHEN chromophores

Dalton transactions (Cambridge, England : 2003), Jan 29, 2016

Five heteroleptic Cu(i)bis(phenanthroline) chromophores with distinct variation in the steric bul... more Five heteroleptic Cu(i)bis(phenanthroline) chromophores with distinct variation in the steric bulk at the 2,9-phenanthroline position were synthesized using the HETPHEN method, and their ground and excited state properties are described. Analysis of the crystal structures reveals a significant distortion from tetrahedral geometry around the Cu(i) centre which is attributed to favourable aromatic interactions between the two phenanthroline ligands. Ultrafast and nanosecond transient optical spectroscopies reveal that the excited state lifetime can be tuned across two orders of magnitude up to 74 nanoseconds in acetonitrile by changing the 2,9-substituent from hydrogen to sec-butyl. X-ray transient absorption spectroscopy at the Cu K-edge confirmed Cu(i) oxidation to Cu(ii) and revealed a decrease of the Cu-N bond lengths in the excited state. The ground and excited state characterization presented here will guide the integration of CuHETPHEN chromophores into complex electron donor-a...

Research paper thumbnail of The optical properties of conjugated materials and their aggregates: towards imaging of films and devices

Physical Chemistry of Interfaces and Nanomaterials XIII, 2014

Research paper thumbnail of The effects of side-chain-induced disorder on the emission spectra and quantum yields of oligothiophene nanoaggregates: a combined experimental and MD-TDDFT study

The journal of physical chemistry. A, Jan 13, 2014

Oligomeric thiophenes are commonly used components in organic electronics and solar cells. These ... more Oligomeric thiophenes are commonly used components in organic electronics and solar cells. These molecules stack and/or aggregate readily under the processing conditions used to form thin films for these applications, significantly altering their optical and charge-transport properties. To determine how these effects depend on the substitution pattern of the thiophene main chains, nanoaggregates of three sexithiophene oligomers having different alkyl substitution patterns were formed using solvent-poisoning techniques and studied using steady-state and time-resolved emission spectroscopy. The results indicate the substantial role played by the side-chain substituents in determining the emissive properties of these species. Both the measured spectral changes and their dependence on substitution are well-modeled by combined quantum chemistry and molecular dynamics simulations. The simulations connect the side-chain-induced disorder, which determines the favorable chain-packing configu...

Research paper thumbnail of Effects of Solvent Properties on the Spectroscopy and Dynamics of Alkoxy-Substituted PPV Oligomer Aggregates

The Journal of Physical Chemistry B, 2012

Conjugated systems are frequently studied in their nanoaggregate form to probe the effects of sol... more Conjugated systems are frequently studied in their nanoaggregate form to probe the effects of solvent and of film formation on their spectral and dynamical properties. This article focuses on the emission spectra and dynamics of nanoaggregates of alkoxy-substituted PPV oligomers with the goal of interpreting the vibronic emission envelopes observed in these systems (J. Phys. Chem. C2009, 113, 18851-18862). The aggregates are formed by adding a nonsolvent such as methanol (MeOH) or water to a solution of the oligomers in a good solvent such as methyl tetrahydrofuran (MeTHF) or tetrahydrofuran (THF). The emission spectra of aggregates formed using either of these combinations exhibit a vibronic pattern in which the ratio of the intensity of highest-energy band to that of the lower energy peaks depends strongly on the ratio of good to poor solvent. In aggregates formed from MeTHF:MeOH, this was shown to be due to the presence of both aggregate-like and monomer-like emitters forming a &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;core&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; and surrounding &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;shell&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;-like structure, respectively, within a single aggregate (J. Phys. Chem. C2011, 115, 15607-15616). In support of this model, the monomer-like emission is shown here to be significantly decreased by changing the solvent pair to the more polar THF:water. This suggests that nanoaggregates formed in THF:water contain a much smaller proportion of monomer-like chains than those formed in MeTHF/MeOH, as would be expected from using a more highly polar nonsolvent. Results from bulk steady-state and time-resolved emission measurements as well as fluorescence lifetime imaging microscopy (FLIM) of the aggregates are shown to be consistent with this interpretation.

Research paper thumbnail of Excited-State Bond Contraction and Charge Migration in a Platinum Dimer Complex Characterized by Xray and Optical Transient Absorption Spectroscopy

Research paper thumbnail of A Theory-guided X-ray Absorption Spectroscopy Approach for Identifying Active Sites in Atomically Dispersed Transition Metal Catalysts

Atomically dispersed supported metal catalysts offer new properties and the benefits of maximized... more Atomically dispersed supported metal catalysts offer new properties and the benefits of maximized metal accessibility and utilization. The characterization of these materials, however, remains challenging. Using atomically-dispersed Pt supported on crystalline MgO (chosen for its well-defined bonding sites for Pt) as a prototypical example, in this work, we demonstrate how systematic density functional theory calculations (for assessing all the potentially stable Pt sites) combined with automated EXAFS analysis can lead to unbiased identification of isolated, surface-enveloped platinum cations as the catalytic species for CO oxidation. The catalyst has been characterized by atomic-resolution imaging, EXAFS, and HERFD-XANES spectroscopies; the proposed Pt site are in full agreement with experiment. This theory-guided workflow leads to rigorously determined structural models and provides a more detailed picture of the structure of the catalytically active sites than what is currently ...

Research paper thumbnail of Identifying Higher Oxygenate Synthesis Sites in Cu Catalysts Promoted and Stabilized by Atomic Layer Deposited Fe2O3

Research paper thumbnail of Understanding Support Effects of ZnO‐Promoted Co Catalysts for Syngas Conversion to Alcohols Using Atomic Layer Deposition

Research paper thumbnail of Reduction and Agglomeration of Supported Metal Clusters Induced by High-Flux X-ray Absorption Spectroscopy Measurements

The Journal of Physical Chemistry C

Research paper thumbnail of Reducing instability in dispersed powder photocatalysis derived from variable dispersion, metallic co-catalyst morphology, and light fluctuations

Journal of Photochemistry and Photobiology

Research paper thumbnail of The Consortium for Operando and Advanced Catalyst Characterization via Electronic Spectroscopy and Structure (Co-ACCESS) at Stanford Synchrotron Radiation Lightsource (SSRL)

Synchrotron Radiation News

Research paper thumbnail of X-ray Snapshots Reveal Conformational Influence on Active Site Ligation During Metalloprotein Folding

Chemical Science

Cytochrome c (cyt c) has long been utilized as a model system to study metalloprotein folding dyn... more Cytochrome c (cyt c) has long been utilized as a model system to study metalloprotein folding dynamics and the interplay between active site ligation and tertiary structure. However, recent reports...

Research paper thumbnail of Revealing Fast Structural Dynamics in pH-Responsive Peptides with Time-Resolved X-ray Scattering

The Journal of Physical Chemistry B

Research paper thumbnail of Investigation of the photoinduced axial ligation process in the excited state of nickel(II) phthalocyanine

Journal of Photochemistry and Photobiology A: Chemistry

Research paper thumbnail of {"__content__"=>"The Nature of the Long-Lived Excited State in a Ni Phthalocyanine Complex Investigated by X-Ray Transient Absorption Spectroscopy.", "sup"=>{"__content__"=>"II"}}

ChemSusChem, Jan 31, 2018

The nature of the photoexcited state of octabutoxy nickel(II) phthalocyanine (NiPcOBu ) with a 50... more The nature of the photoexcited state of octabutoxy nickel(II) phthalocyanine (NiPcOBu ) with a 500 ps lifetime was investigated by X-ray transient absorption (XTA) spectroscopy. Previous optical, vibrational, and computational studies have suggested that this photoexcited state has a ligand-to-metal charge transfer (LMCT) nature. By using XTA, which provides unambiguous information on the local electronic and nuclear configuration around the Ni center, the nature of the excited state of NiPcOBu was reassessed. Using X-ray probe pulses from a synchrotron source, the ground- and excited-state X-ray absorption spectra of NiPcOBu were measured. Based on the results, we identified that the excited state exhibits spectral features that are characteristic of a Ni (3dz2 ,3dx2-y2 ) state rather than a LMCT state with a transiently reduced Ni center. This state resembles the (d,d) state of nickel(II) tetramesitylphorphyrin. The XTA features are rationalized based on the inherent cavity sizes ...

Research paper thumbnail of Insulin hexamer dissociation dynamics revealed by photoinduced T-jumps and time-resolved X-ray solution scattering

Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, Jan 11, 2018

The structural dynamics of insulin hexamer dissociation were studied by the photoinduced temperat... more The structural dynamics of insulin hexamer dissociation were studied by the photoinduced temperature jump technique and monitored by time-resolved X-ray scattering. The process of hexamer dissociation was found to involve several transient intermediates, including an expanded hexamer and an unstable tetramer. Our findings provide insights into the mechanisms of protien-protein association.

Research paper thumbnail of Probing Cytochrome c Folding Transitions upon Phototriggered Environmental Perturbations Using Time-Resolved X-ray Scattering

The journal of physical chemistry. B, Jan 15, 2018

Direct tracking of protein structural dynamics during folding-unfolding processes is important fo... more Direct tracking of protein structural dynamics during folding-unfolding processes is important for understanding the roles of hierarchic structural factors in the formation of functional proteins. Using cytochrome c (cyt c) as a platform, we investigated its structural dynamics during folding processes triggered by local environmental changes (i.e., pH or heme iron center oxidation/spin/ligation states) with time-resolved X-ray solution scattering measurements. Starting from partially unfolded cyt c, a sudden pH drop initiated by light excitation of a photoacid caused a structural contraction in microseconds, followed by active site restructuring and unfolding in milliseconds. In contrast, the reduction of iron in the heme via photoinduced electron transfer did not affect conformational stability at short timescales (<1 ms), despite active site coordination geometry changes. These results demonstrate how different environmental perturbations can change the nature of interaction b...

Research paper thumbnail of Electronic and nuclear contributions to time-resolved optical and X-ray absorption spectra of hematite and insights into photoelectrochemical performance

Energy Environ. Sci.

Spectra show both transient photocarriers and lattice heating.

Research paper thumbnail of Direct Observation of Insulin Association Dynamics with Time-Resolved X-ray Scattering

The Journal of Physical Chemistry Letters

Biological functions frequently require protein-protein interactions that involve secondary and t... more Biological functions frequently require protein-protein interactions that involve secondary and tertiary structural perturbation. Here we study protein-protein dissociation and reassociation dynamics in insulin, a model system for protein oligomerization. Insulin dimer dissociation into monomers was induced by a nanosecond temperature-jump (T-jump) of ∼8 °C in aqueous solution, and the resulting protein and solvent dynamics were tracked by time-resolved X-ray solution scattering (TRXSS) on time scales of 10 ns to 100 ms. The protein scattering signals revealed the formation of five distinguishable transient species during the association process that deviate from simple two-state kinetics. Our results show that the combination of T-jump pump coupled to TRXSS probe allows for direct tracking of structural dynamics in nonphotoactive proteins.

Research paper thumbnail of Solution Structures of Highly Active Molecular Ir Water-Oxidation Catalysts from Density Functional Theory Combined with High-Energy X-Ray Scattering and EXAFS Spectroscopy

Journal of the American Chemical Society, May 18, 2016

The solution structures of highly active Ir water-oxidation catalysts are elucidated by combining... more The solution structures of highly active Ir water-oxidation catalysts are elucidated by combining density functional theory, high-energy X-ray scattering (HEXS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. We find that the catalysts are Ir dimers with mono-μ-oxo cores and terminal anionic ligands, generated in situ through par-tial oxidation of a common catalyst precursor. The pro-posed structures are supported by 1H and 17O NMR, EPR, resonance Raman and UV-visible spectra, electrophoresis, etc. Our findings are particularly valuable to understand the mechanism of water oxidation by highly reactive Ir catalysts. Importantly, our DFT-EXAFS-HEXS methodology provides a new in-situ technique for characterization of active species in catalytic systems.

Research paper thumbnail of Synthesis, structure, ultrafast kinetics, and light-induced dynamics of CuHETPHEN chromophores

Dalton transactions (Cambridge, England : 2003), Jan 29, 2016

Five heteroleptic Cu(i)bis(phenanthroline) chromophores with distinct variation in the steric bul... more Five heteroleptic Cu(i)bis(phenanthroline) chromophores with distinct variation in the steric bulk at the 2,9-phenanthroline position were synthesized using the HETPHEN method, and their ground and excited state properties are described. Analysis of the crystal structures reveals a significant distortion from tetrahedral geometry around the Cu(i) centre which is attributed to favourable aromatic interactions between the two phenanthroline ligands. Ultrafast and nanosecond transient optical spectroscopies reveal that the excited state lifetime can be tuned across two orders of magnitude up to 74 nanoseconds in acetonitrile by changing the 2,9-substituent from hydrogen to sec-butyl. X-ray transient absorption spectroscopy at the Cu K-edge confirmed Cu(i) oxidation to Cu(ii) and revealed a decrease of the Cu-N bond lengths in the excited state. The ground and excited state characterization presented here will guide the integration of CuHETPHEN chromophores into complex electron donor-a...

Research paper thumbnail of The optical properties of conjugated materials and their aggregates: towards imaging of films and devices

Physical Chemistry of Interfaces and Nanomaterials XIII, 2014

Research paper thumbnail of The effects of side-chain-induced disorder on the emission spectra and quantum yields of oligothiophene nanoaggregates: a combined experimental and MD-TDDFT study

The journal of physical chemistry. A, Jan 13, 2014

Oligomeric thiophenes are commonly used components in organic electronics and solar cells. These ... more Oligomeric thiophenes are commonly used components in organic electronics and solar cells. These molecules stack and/or aggregate readily under the processing conditions used to form thin films for these applications, significantly altering their optical and charge-transport properties. To determine how these effects depend on the substitution pattern of the thiophene main chains, nanoaggregates of three sexithiophene oligomers having different alkyl substitution patterns were formed using solvent-poisoning techniques and studied using steady-state and time-resolved emission spectroscopy. The results indicate the substantial role played by the side-chain substituents in determining the emissive properties of these species. Both the measured spectral changes and their dependence on substitution are well-modeled by combined quantum chemistry and molecular dynamics simulations. The simulations connect the side-chain-induced disorder, which determines the favorable chain-packing configu...

Research paper thumbnail of Effects of Solvent Properties on the Spectroscopy and Dynamics of Alkoxy-Substituted PPV Oligomer Aggregates

The Journal of Physical Chemistry B, 2012

Conjugated systems are frequently studied in their nanoaggregate form to probe the effects of sol... more Conjugated systems are frequently studied in their nanoaggregate form to probe the effects of solvent and of film formation on their spectral and dynamical properties. This article focuses on the emission spectra and dynamics of nanoaggregates of alkoxy-substituted PPV oligomers with the goal of interpreting the vibronic emission envelopes observed in these systems (J. Phys. Chem. C2009, 113, 18851-18862). The aggregates are formed by adding a nonsolvent such as methanol (MeOH) or water to a solution of the oligomers in a good solvent such as methyl tetrahydrofuran (MeTHF) or tetrahydrofuran (THF). The emission spectra of aggregates formed using either of these combinations exhibit a vibronic pattern in which the ratio of the intensity of highest-energy band to that of the lower energy peaks depends strongly on the ratio of good to poor solvent. In aggregates formed from MeTHF:MeOH, this was shown to be due to the presence of both aggregate-like and monomer-like emitters forming a &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;core&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; and surrounding &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;shell&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;-like structure, respectively, within a single aggregate (J. Phys. Chem. C2011, 115, 15607-15616). In support of this model, the monomer-like emission is shown here to be significantly decreased by changing the solvent pair to the more polar THF:water. This suggests that nanoaggregates formed in THF:water contain a much smaller proportion of monomer-like chains than those formed in MeTHF/MeOH, as would be expected from using a more highly polar nonsolvent. Results from bulk steady-state and time-resolved emission measurements as well as fluorescence lifetime imaging microscopy (FLIM) of the aggregates are shown to be consistent with this interpretation.