| 1. |
- Björk, Per, et al.
(author)
-
Oligothiophene Assemblies Defined by DNA Interaction : From Single Chains to Disordered Clusters
- 2009
-
In: SMALL. - : Wiley. - 1613-6810 .- 1613-6829. ; 5:1, s. 96-103
-
Journal article (peer-reviewed)abstract
- The organization of conjugated polyelectrolytes (CPEs) interacting with biomolecules sets conditions for the biodetection of biological processes and identity, through the use of optical emission from the CPE. Herein, a well-defined CPE and its binding to DNA is studied. By using dynamic light scattering and circular dichroism spectroscopy, it is shown that the CPE forms a multimolecule ensemble in aqueous solution that is more than doubled it? size when interacting with a small DNA chain, while single chains are evident in ethanol. The related changes in the fluorescence spectra upon polymer aggregation are assigned to oscillator strength redistribution between vibronic transitions in weakly coupled H-aggregates. An enhanced single-molecule spectroscopy technique that allows full control of excitation and emission light polarization is applied to combed and decorated;,DNA chains. It is found that the organization of combed CPE-lambda DNA complexes (when dry on the surface) allows considerable variation of CPE distances and direction relative to the DNA chain. By analysis of the polarization data. energy transfer between the polymer chains in individual complexes is confirmed and their sizes estimated.
|
|
| 2. |
|
|
| 3. |
- Herland, Anna, et al.
(author)
-
Decoration of amyloid fibrils with luminescent conjugated polymers
- 2008
-
In: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 18:1, s. 126-132
-
Journal article (peer-reviewed)abstract
- In this work we report the coating of a biological template with a polar, but uncharged, luminescent conjugated polymer, soluble in organic solvents but not in water, to produce a nanowire. Amyloid fibrils from bovine insulin were decorated with an alternating polyfluorene derivative. Decorated fibrils were partially aligned on hydrophobic surfaces as separate and bundled fibrils, by means of molecular combing. The single molecule spectroscopy technique utilizing excitation by rotating linearly polarized light and fluorescence detection through a rotating polarizer showed a high degree of anisotropy of the polymer chains on the individual fibrils. The high degree of polarization indicated highly oriented polymer chains with the preferential orientation of the polymer backbone along the fibrils. The anisotropy ratios are comparable with those of well-oriented polymer chains in films. © The Royal Society of Chemistry.
|
|
| 4. |
- Huang, Weiming, et al.
(author)
-
Assessment and benchmarking of spatially enabled RDF stores for the next generation of spatial data infrastructure
- 2019
-
In: ISPRS International Journal of Geo-Information. - : MDPI AG. - 2220-9964. ; 8:7
-
Journal article (peer-reviewed)abstract
- Geospatial information is indispensable for various real-world applications and is thus a prominent part of today’s data science landscape. Geospatial data is primarily maintained and disseminated through spatial data infrastructures (SDIs). However, current SDIs are facing challenges in terms of data integration and semantic heterogeneity because of their partially siloed data organization. In this context, linked data provides a promising means to unravel these challenges, and it is seen as one of the key factors moving SDIs toward the next generation. In this study, we investigate the technical environment of the support for geospatial linked data by assessing and benchmarking some popular and well-known spatially enabled RDF stores (RDF4J, GeoSPARQL-Jena, Virtuoso, Stardog, and GraphDB), with a focus on GeoSPARQL compliance and query performance. The tests were performed in two different scenarios. In the first scenario, geospatial data forms a part of a large-scale data infrastructure and is integrated with other types of data. In this scenario, we used ICOS Carbon Portal’s metadata—a real-world Earth Science linked data infrastructure. In the second scenario, we benchmarked the RDF stores in a dedicated SDI environment that contains purely geospatial data, and we used geospatial datasets with both crowd-sourced and authoritative data (the same test data used in a previous benchmark study, the Geographica benchmark). The assessment and benchmarking results demonstrate that the GeoSPARQL compliance of the RDF stores has encouragingly advanced in the last several years. The query performances are generally acceptable, and spatial indexing is imperative when handling a large number of geospatial objects. Nevertheless, query correctness remains a challenge for cross-database interoperability. In conclusion, the results indicate that the spatial capacity of the RDF stores has become increasingly mature, which could benefit the development of future SDIs.
|
|
| 5. |
- Lin, Hongzhen, et al.
(author)
-
Fate of Excitations in Conjugated Polymers : Single-Molecule Spectroscopy Reveals Nonemissive "Dark" Regions in MEH-PPV Individual Chains
- 2009
-
In: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 9:12, s. 4456-4461
-
Journal article (peer-reviewed)abstract
- Single chains of the conjugated polymer MEH-PPV (poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene)) were studied with wide-field fluorescence microscopy (dispersion in inert polymer matrices) and with fluorescence correlation spectroscopy (chloroform solution). The fluorescence yield of individual molecules in matrices was found to be 1-2 orders of magnitude lower than that in solution and it decreased substantially with increasing chain length. It suggests that isolation of MEH-PPV molecules in polymer matrices creates favorable conditions for photogeneration of nonemissive primary excited states.
|
|
| 6. |
- Lin, Hongzhen, et al.
(author)
-
Fluorescence blinking, exciton dynamics, and energy transfer domains in single conjugated polymer chains.
- 2008
-
In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 130:22, s. 7042-7051
-
Journal article (peer-reviewed)abstract
- In order to understand exciton migration and fluorescence intensity fluctuation mechanisms in conjugated polymer single molecules, we studied fluorescence decay dynamics at "on" and "off" fluorescence intensity levels with 20 ps time resolution using MEH-PPV [poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] dispersed in PMMA. Two types of intensity fluctuations were distinguished for single chains of conjugated polymers. Abrupt intensity fluctuations (blinking) were found to be always accompanied by corresponding changes in fluorescence lifetime. On the contrary, during "smooth" intensity fluctuations no lifetime change was observed. Time-resolved data in combination with data on fluorescence emission and excitation anisotropy lead to a picture where a single polymer molecule is seen as consisting of several energy transfer domains. Exciton migration is efficient within a domain and not efficient between domains. Each domain can have several emitting low-energy sites over which the exciton continuously migrates until it decays. Emission of individual domains is often highly polarized. Fluorescence from a domain can be strongly quenched by Forster energy transfer to a quencher (hole polaron) if the domain overlaps with the quenching sphere.
|
|
| 7. |
- Lin, Hongzhen, et al.
(author)
-
Single chain versus single aggregate spectroscopy of conjugated polymers. Where is the border?
- 2010
-
In: Physical chemistry chemical physics : PCCP. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 12, s. 11770-11777
-
Journal article (peer-reviewed)abstract
- Single chains of conjugated polymers e.g. MEH-PPV (poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) have become interesting objects for single molecule spectroscopy (SMS) studies. However, most of the experiments so far were performed without full awareness of the isolation status of the polymer chains in host matrices. We used steady-state and time-resolved fluorescence methods and 2D polarization single molecule imaging technique to unravel the isolation/aggregation status of MEH-PPV in spin-coated films prepared at different conditions. It turned out that a sample showing isolated bright spots in fluorescence images could be obtained in a very broad concentration range of MEH-PPV when toluene was used as a solvent and PMMA as a matrix. If the MEH-PPV concentration was not sufficiently low, a substantial fraction of the fluorescence spots should be assigned to individual nano-aggregates rather than truly isolated chains of the polymer. Contrary to single aggregates, truly isolated MEH-PPV chains showed blue-shifted emission spectra, mono-exponential fluorescence decay dynamics with relatively long lifetimes (0.4-1.2 ns), and high polarization anisotropy. We argue that insufficient control of the concentration in the published SMS studies of MEH-PPV resulted in incorrect assigning of some spectroscopic properties of single aggregates to isolated MEH-PPV chains. We believe this to be the main origin of discrepancies among the published data in this field.
|
|
| 8. |
- Mirzov, Oleg, et al.
(author)
-
Direct exciton quenching in single molecules of MEH-PPV at 77 K
- 2004
-
In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 386:4-6, s. 286-290
-
Journal article (peer-reviewed)abstract
- Fluorescence blinking behaviour was observed for single molecules of the conjugated polymer poly[2-methoxy,5-(2'-ethylhexyloxy)-p-phenylene-vinylene] (MEH-PPV) at 77 and 300 K. No strict qualitative dependence on temperature was observed, despite of the expected suppression of exciton migration at the low temperature. We assume MEH-PPV molecules to form dense nanoparticles with a characteristic size of about 10 nm at the largest. In such small nanoparticles exciton can be efficiently quenched by a photogenerated quencher due to Forster transfer just after a few hops over the polymer nanoparticle. Thus, long-distance exciton migration is not necessary to have strong fluorescence intensity fluctuations. (C) 2004 Elsevier B.V. All rights reserved.
|
|
| 9. |
- Mirzov, Oleg, et al.
(author)
-
Fluorescence blinking in MEH-PPV single molecules at low temperature
- 2005
-
In: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 112:1-4, s. 353-356
-
Journal article (peer-reviewed)abstract
- Fluorescence intensity transients of single molecules of the conjugated polymer poly[2-methoxy,5-(2-ethylhexyloxy)-p-phenylene-vinylene] (MEH-PPV) were studied at 15 K. Fluorescence blinking behavior was observed despite the expected low-temperature suppression of energy migration in such disordered molecular systems. Presence of the fluorescence blinking effect at 15K indicates that the single molecules possess a collapsed conformation with characteristic size of not more than several nanometers, which corresponds to only a few exciton hops over a polymer chain. (c) 2004 Elsevier B.V. All rights reserved.
|
|
| 10. |
- Mirzov, Oleg, et al.
(author)
-
Large spectral diffusion of conjugated polymer single molecule fluorescence at low temperature
- 2005
-
In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 408:4-6, s. 317-321
-
Journal article (peer-reviewed)abstract
- The conductive polymer poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4- phenylene vinylene) (MEH-PPV) was investigated by means of single molecule spectroscopy at 15 K. MEH-PPV single chains were deposited onto a surface from a toluene solution and covered with a polymer cap layer spin-coated from an aqueous solution for protection from air. The MEH-PPV molecules exhibited large fluorescence spectral diffusion with the range reaching 1000 cm(-1). We concluded that conformational changes, affecting dispersive interactions and conjugation length, is the most probable mechanism of the observed effect. It is the matrix-free environment that allows the MEH-PPV chains to undergo sufficiently large conformational changes even at low temperature. (c) 2005 Elsevier B.V. All rights reserved.
|
|
| 11. |
- Mirzov, Oleg, et al.
(author)
-
Photoluminescence spectra of a conjugated polymer: from films and solutions to single molecules
- 2006
-
In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 8:47, s. 5569-5576
-
Journal article (peer-reviewed)abstract
- The purpose of this work is to address the issue of applicability of single-molecule spectroscopy (SMS) results for conjugated polymers to "bulk" samples, e.g. conjugated polymer films. Also, some apparent inconsistencies in the literature on SMS regarding the photoluminescence spectral position of conjugated polymers are discussed. We present a series of photoluminescence spectra of thin films of the conjugated polymer poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) with a wide range of varying thickness. The thickness was varied from similar to 20 nm to the value corresponding to well-separated single molecules (SMS sample). The thickness variation resulted in a strong (similar to 2000 cm(-1)) blue-shift and broadening of the spectrum. The result was reproduced on isolated molecules embedded into a PMMA matrix. This effect cannot be explained by a decrease in energy transfer "freedom" alone. We performed a comprehensive comparison of presented and elsewhere published spectra of MEH-PPV polymer and oligomers in different samples: films, solutions, isolated-molecule coatings and standard SMS samples. The comparison allows that the main reason behind the blue shift is conformational disorder, which is largely dependent on the sample. We also discuss some experimental aspects of SMS, such as representativeness of detected molecules, spectral sensitivity of a setup and temperature. Together with differences in sample preparation method, these issues can explain the existing inconsistencies in the literature.
|
|
| 12. |
- Mirzov, Oleg, et al.
(author)
-
Polarization Portraits of Single Multichromophoric Systems: Visualizing Conformation and Energy Transfer.
- 2009
-
In: Small. - : Wiley. - 1613-6829 .- 1613-6810. ; 5, s. 1877-1888
-
Journal article (peer-reviewed)abstract
- A novel technique, two-dimensional (2D) polarization single-molecule imaging, is presented. It is based on measurements and analysis of fluorescence intensity as a function of excitation and emission polarization angles. The technique allows recording of full information on the steady-state polarization properties of fluorescent objects. It is particularly suitable for application to single multichromophoric systems (molecules or nanoparticles) with energy transfer (ET) between different chromophores (e.g., single fluorescent pi-conjugated polymer chains). The 2D polarization data simultaneously provide information on the conformation of the system and the efficiency of its internal excitation ET. The technique is used to characterize single chains and different kinds of chain aggregates of different conjugated polymers at different temperatures. The 2D polarization measurements reveal a dramatic difference in ET taking place in these systems. Clear temperature dependence of ET is observed for individual aggregates as well as for their statistical ensembles. Also, a dependence on solvent and aggregate size is shown. Additionally, extensive "traditional one-dimensional" polarization results on the polarization anisotropy of fluorescence excitation and emission are presented. These results and findings are discussed in relation to internal organization of the nano-objects under study.
|
|
| 13. |
- Mirzov, Oleg, et al.
(author)
-
Polydispersity of the photoluminescence quantum yield in single conjugated polymer chains
- 2005
-
In: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 318:3, s. 217-222
-
Journal article (peer-reviewed)abstract
- The conjugated polymer poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-pheiiylene vinylene) (MEH-PPV) was studied by a single-molecule imaging technique. A comparison of statistical distributions of fluorescence intensity with molecular weight distributions revealed that the distribution of the photoluminescence quantum yield of the single polymer chains under study is significantly asymmetric, with a polydispersity greater than or similar to 2. The result implies that there are molecules whose quantum yield is a few times higher than the ensemble quantum yield. This conclusion Suggests a possibility of a great improvement of the photoluminescence quantum yield of MEH-PPV, which is known to be several times less than 1. (c) 2005 Elsevier B.V.. All rights reserved.
|
|
| 14. |
- Mirzov, Oleg
(author)
-
Single-molecule spectroscopy of π-conjugated polymers
- 2008
-
Doctoral thesis (other academic/artistic)abstract
- When applied to condensed-matter samples of large organic molecules, optical spectroscopy faces the problem of inhomogeneous broadening caused by the diversity of environments and conformations that sample molecules are subjected to. This severely limits the information that can be extracted from optical spectra. Single-molecule spectroscopy offers the most natural way to overcome this problem. Π-conjugated polymers are a class of photoluminescent materials whose electronic structure is similar to that of semiconductors, which makes them promising materials for a range of applications. Spectroscopically, they are multicromophoric systems showing individual photophysical properties due to efficient excitation energy transfer to a small number of fluorescent exciton traps. This makes them a natural object to study with single-molecule spectroscopy. This thesis presents a series of results obtained with a range of single-molecule spectroscopy-based techniques on the model conjugated polymer MEH-PPV. Single-chain fluorescence intensity fluctuations (blinking), fluorescence spectral diffusion, fluorescence kinetics and polarization properties have been observed and investigated. Apart from the pristine single-molecule spectroscopy, the range of techniques included: single-molecule imaging (low temporal resolution), time-correlated single photon counting (high temporal resolution) and a novel technique – 2D polarization single-molecule imaging – which is being reported in detail for the first time. Most of the techniques have been combined with temperature-dependent measurements (from 15 K on). Other types of samples (e.g. chain aggregates and submonolayer films) have been studied for comparison, too. In addition, a technique for simulating the photophysical properties of the polymer chains by simple and computationally affordable means is presented.
|
|
| 15. |
- Pullerits, Tönu, et al.
(author)
-
Conformational fluctuations and large fluorescence spectral diffusion in conjugated polymer single chains at low temperatures
- 2005
-
In: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 109:41, s. 19099-19107
-
Journal article (peer-reviewed)abstract
- The fluorescence of single chains of the conductive polymer poly [2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) was studied by means of single-molecule spectroscopy at 15 K. MEH-PPV was deposited onto a surface from a toluene solution and covered with a polymer cap layer of poly(vinyl alcohol) spin-coated from an aqueous solution for protection against air. Because MEH-PPV is insoluble in water, such sample preparation guarantees that MEH-PPV chains do not mix with the cap polymer. We found that this "host matrix free" environment results in substantially stronger fluorescence spectral diffusion than that observed for conjugated polymer single chains embedded into polymer matrices. The average spectral diffusion range was 500 cm(-1), and the maximum registered value reached 1100 cm(-1), which is similar to 6 times larger than the values reported before. We analyzed spectral diffusion by observation of temporal evolution of the fluorescence intensity, the position of the maximum, and the width of fluorescence spectra. We propose that the transition energy shifts are caused by the differences of the London dispersive forces in slightly different polymer chain conformations. Such conformational changes are possible even at low temperatures because the MEH-PPV single chains in our samples have more freedom for fluctuations than in the usual "in host" arrangement.
|
|
| 16. |
- Vermeulen, Alex, et al.
(author)
-
ENVRI-FAIR D8.7: The FAIRness of ICOS
- 2023
-
Reports (other academic/artistic)abstract
- This report presents the extended implementation of the FAIR principles by ICOS Atmosphere during the ENVRI-FAIR project.
|
|
