Photochrome-doped organic films for photonic key-pad locks and multi-state fluorescence

The spectroscopic properties of poly(methyl methacrylate) polymer films doped with two kinds of photochromic molecular switches are investigated. A green-fluorescent sulfonyl diarylethene (P1) is combined with either a non-fluorescent diarylethene (P2) or red-fluorescent spiropyran (P3). Photoswitching between the colorless and colored isomers (P1: o-BTFO4 ↔ c-BTFO4, P2: o-DTE ↔ c-DTE, P3: SP ↔ MC) enables the P1+P2 and P1+P3 films to be cycled through three distinct states. From the initial state (o-BTFO4 + o-DTE/SP), irradiation with UV light generates the second state (c-BTFO4 + c-DTE/MC), where c-BTFO4 → c-DTE/MC energy transfer is established. Irradiation with green light then generates the third state (c-BTFO4 + o-DTE/SP), where the energy transfer acceptor is no longer present. Finally, irradiation with blue light regenerates the initial state. For the P1+P2 film, only one state is fluorescent, with the irradiation inputs required to be entered in the correct order to access this state, acting as a keypad lock. For the P1+P3 film, the states emit either no fluorescence, red fluorescence, or green fluorescence, all using a common excitation wavelength. Additionally, once the fluorescence is activated with UV light, it undergoes a time-dependent color transition from red to green, due to the pairing of P-type and T-type photochromes. These multi-photochromic systems may be useful for security ink or imaging applications

Time-resolved and polarised fluorescence studies of polymeric and biological systems

© 2018 Dr. Hamid SoleimaninejadUnderstanding the dynamics of energy migration for disordered complex systems such as polymeric solar cells is crucial for optimizing the charge transport process and obtaining efficient devices. Fluorescence anisotropy provides information on the mobility and orientation of the bio-molecules and has been used to investigate protein–protein interactions. Despite recent exploration and advances in techniques, the dynamics of fluorescence depolarisation in complex systems are not yet fully comprehended. This thesis reports a new strategy to map the fluorescence anisotropy and investigate the energy migration and macromolecular rotational diffusion in polymeric and biological systems. A fluorescence anisotropy imaging microscopy (FAIM) method combined with fluorescence lifetime imaging (FLIM), and evanescent wave time-resolved fluorescence anisotropy measurements (EW-TRAM) to explore the photophysics associated with morphological changes in a wide range of complex systems such as conjugated polymers, cells and soft bilayers. First of all, the morphology and photophysics of aggregation in MEH-PPV conjugated polymer films cast by a controlled evaporative self-assembly “Snake-Skin” method have been investigated. FLIM and FAIM were used to monitor the photophysical changes and also depolarisation of emission, respectively. The tightly packed and coiled conformation regions in films were identified by shorter lifetime and lower emission anisotropy histograms. Also, the open chain conformation could be detected by observing high values of lifetime and anisotropy. In addition, a systematic visualization of the unique photophysical and fluorescence anisotropic features of polyfluorene coplanar conformation (beta-conformation) are demonstrated. Inhomogeneous morphologies and fluorescence decay profiles at diverse micrometre-sized regions within all types of polyfluorene beta-conformational spin-coated films have been distinguished. PFO and PODPF beta-domains both had shorter emission lifetimes than those of the glassy conformation. In addition, beta-conformational regions had larger fluorescence anisotropy due to high chain orientation, while the low anisotropy in glassy conformational regions showed efficient energy migration from amorphous regions to beta-conformation as a whole. Moreover, TREWIFS and EW-TRAMs methods were utilised to study the interaction of melittin peptide with POPC and POPG vesicles on a silica interface. The emission decay time of NBD dye attached to the peptide was carefully monitored using the TCSPC method. Different fluorescence decay profiles were observed during depth profiling from interface in tens of nanometre increments. The fluorescence decay kinetics of all systems was found to be multi-exponential. Change of lifetime and rotational correlation time even in nanometre increments revealed the accuracy and power of the method. In addition, investigations demonstrate the ability of the method to detect changes in morphology of peptide-LUVs during interactions with interface. Finally, a new method was developed to allow spatiotemporal visualization of the macromolecular crowding effect in cells. An amine-reactive aggregation-induced emission fluorogen (AIE) was used to label proteins in the cytoplasm. The change in the protein mobility as well as local viscosity was monitored by using FAIM and FLIM, respectively. The effect of osmotic stress on the cytoplasmic crowding in fixed Neuro-2A cells, treated with sorbitol at different concentrations was explored. Real time monitoring of cytoplasmic crowding effect in live cells showed the anisotropy histogram was shifted to higher values due to dense protein packing environments after sorbitol treatment. Total internal reflection fluorescence microscopy (TIRFM) was incorporated with FAIM to track morphological modifications during “Statin” drug treatments. FLIM results of CHO-K1 cells treated with different doses of statin drug exhibited minor changes in fluorescence lifetime histogram. Highly oriented F-actin filaments in cells (10 µM ) lovastatin treatment displayed shorter mean lifetime and higher anisotropy in comparison with control cells. In addition, total internal reflection fluorescence anisotropy measurements (TIRFAM) exhibited the elevated fluorescence anisotropy in cells treated with (10 µM) lovastatin compared to the cells treated with (5 µM) lovastatin. In conclusion, the results of this thesis showed how FAIM, FLIM and EW-TRAM can be employed as promising approaches toward the successful morphological investigation in polymeric and biological complex systems

Fluorescence Anisotropy Imaging of a Polydiacetylene Photopolymer Film.

UV-illumination of phase-separated surfactant films prepared from mixtures of photopolymerizable 10, 12-Pentacosadiynoic acid and perfluorotetradecanoic acid results in the formation of fluorescent polydiacetylene fibers and aggregates. In this work, the orientation of polymer strands that comprise the resulting photopolymer structures has been probed using fluorescence anisotropy imaging in combination with defocused single-molecule fluorescence imaging. Imaging experiments indicate the presence of significant fiber-to-fiber heterogeneity, as well as anisotropy within each fiber (or aggregate), with both of these properties changing as a function of film preparation conditions. This anisotropy can be attributed to various alignments of the constituent polymer strands that comprise the larger fibers and aggregates. Intriguingly, when using defocused imaging, fiber images consisted of a series of discrete â doughnutâ fluorescence emission patterns, which exhibited intermittent on-off blinking behavior; both of these properties are characteristic of individual emission transition dipoles (single-molecules). Further, all of the individual emission transition dipoles had a uniform orientation with respect to the axis of the fiber, indicating a common orientation of discrete emitters in the larger polymer fiber. The implications of these results for future studies of the electronic properties of conjugated polymers in larger macroscopic systems is noted.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Type B CTD Proteins Secreted by the Type IX Secretion System Associate with PorP-like Proteins for Cell Surface Anchorage

The Bacteroidetes type IX secretion system (T9SS) consists of at least 20 components that translocate proteins with type A or type B C-terminal domain (CTD) signals across the outer membrane (OM). While type A CTD proteins are anchored to the cell surface via covalent linkage to the anionic lipopolysaccharide, it is still unclear how type B CTD proteins are anchored to the cell surface. Moreover, very little is known about the PorE and PorP components of the T9SS. In this study, for the first time, we identified a complex comprising the OM β-barrel protein PorP, the OM-associated periplasmic protein PorE and the type B CTD protein PG1035. Cross-linking studies supported direct interactions between PorE-PorP and PorP-PG1035. Furthermore, we show that the formation of the PorE-PorP-PG1035 complex was independent of PorU and PorV. Additionally, the Flavobacterium johnsoniae PorP-like protein, SprF, was found bound to the major gliding motility adhesin, SprB, which is also a type B CTD protein. Together, these results suggest that type B-CTD proteins may anchor to the cell surface by binding to their respective PorP-like proteins

Highly Fluorescent Molecularly Insulated Perylene Diimides: Effect of Concentration on Photophysical Properties

A series of four perylene diimide (PDI) chromophores were prepared with increasing steric bulk on the imide substituents with the aim of retarding the effect of concentration quenching on photoluminescence, commonly observed with these dyes. Spectroscopic investigations of the compounds in dilute solution confirmed that the photophysical properties of the PDI core chromophore were not perturbed by the bulky substituents. Solid film samples containing the PDI compounds at various concentrations dispersed in a poly­(methyl methacrylate) (PMMA) matrix were examined and compared to amorphous neat films as well as crystalline samples. The PDI compounds containing di-<i>tert</i>-butylphenyl (bPDI-3) and trityl (bPDI-4) substituents showed near unity photoluminescence quantum yield (PLQY) up to 20 mM in PMMA compared to 10% PLQY for the reference compound (bPDI-1) without molecular insulation. Surprisingly, high concentrations (>40 mM) of a phenyl-substituted PDI compound (bPDI-2) with moderate molecular insulation formed emissive aggregates that showed a higher PLQY compared to the PDI derivatives with greater steric bulk. By examining the molecular structure and solid state packing in conjunction with a series of photophysical measurements, new insights into designing highly fluorescent dyes, particularly in the solid state, were obtained. The trityl-substituted PDI compound (bPDI-4) was used in a luminescent solar concentrator with optical quantum efficiency of 54%, flux gain of 6.4, and geometric gain of 45

Highly Fluorescent Molecularly Insulated Perylene Diimides: Effect of Concentration on Photophysical Properties

A series of four perylene diimide (PDI) chromophores were prepared with increasing steric bulk on the imide substituents with the aim of retarding the effect of concentration quenching on photoluminescence, commonly observed with these dyes. Spectroscopic investigations of the compounds in dilute solution confirmed that the photophysical properties of the PDI core chromophore were not perturbed by the bulky substituents. Solid film samples containing the PDI compounds at various concentrations dispersed in a poly­(methyl methacrylate) (PMMA) matrix were examined and compared to amorphous neat films as well as crystalline samples. The PDI compounds containing di-<i>tert</i>-butylphenyl (bPDI-3) and trityl (bPDI-4) substituents showed near unity photoluminescence quantum yield (PLQY) up to 20 mM in PMMA compared to 10% PLQY for the reference compound (bPDI-1) without molecular insulation. Surprisingly, high concentrations (>40 mM) of a phenyl-substituted PDI compound (bPDI-2) with moderate molecular insulation formed emissive aggregates that showed a higher PLQY compared to the PDI derivatives with greater steric bulk. By examining the molecular structure and solid state packing in conjunction with a series of photophysical measurements, new insights into designing highly fluorescent dyes, particularly in the solid state, were obtained. The trityl-substituted PDI compound (bPDI-4) was used in a luminescent solar concentrator with optical quantum efficiency of 54%, flux gain of 6.4, and geometric gain of 45

Energy Migration in Organic Solar Concentrators with a Molecularly Insulated Perylene Diimide

Maintaining high incident light absorption while minimizing luminescence reabsorption is a key challenge for organic luminescent solar concentrators (LSCs). Energy migration and trapping using light-harvesting donors and a low-energy highly emitting acceptor is one strategy to reduce the reabsorption issue. However, concentration quenching and the potential formation of quenching aggregates is a limiting factor in realizing efficient devices. We describe the synthesis of a novel molecularly insulated perylene diimide that can resist luminescence quenching at concentrations in excess of 50 mM. Photophysical measurements show the insulated perylene diimide has an excitation energy migration diffusion length of 230 ± 10 Å at 60 mM in poly­(methyl methacrylate). LSC devices using a mixture of the insulated perylene diimide light absorber and perylene red (LR305) as the low-energy trap emitter exhibit reduced reabsorption and a better current output than LR305 only devices. The results demonstrate that appropriately designed organic molecule dyes can potentially meet the stringent requirements required for efficient LSCs

Photophysical and Fluorescence Anisotropic Behavior of Polyfluorene β‑Conformation Films

We demonstrate a systematic visualization of the unique photophysical and fluorescence anisotropic properties of polyfluorene coplanar conformation (β-conformation) using time-resolved scanning confocal fluorescence imaging (FLIM) and fluorescence anisotropy imaging microscopy (FAIM) measurements. We observe inhomogeneous morphologies and fluorescence decay profiles at various micrometer-sized regions within all types of polyfluorene β-conformational spin-coated films. Poly­(9,9-dioctylfluorene-2,7-diyl) (PFO) and poly­[4-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]-<i>co</i>-[5-(octyloxy)-9,9-diphenylfluoren-2,7-diyl] (PODPF) β-domains both have shorter lifetime than those of the glassy conformation for the longer effective conjugated length and rigid chain structures. Besides, β-conformational regions have larger fluorescence anisotropy for the low molecular rotational motion and high chain orientation, while the low anisotropy in glassy conformational regions shows more rotational freedom of the chain and efficient energy migration from amorphous regions to β-conformation as a whole. Finally, ultrastable ASE threshold in the PODPF β-conformational films also confirms its potential application in organic lasers. In this regard, FLIM and FAIM measurements provide an effective platform to explore the fundamental photophysical process of conformational transitions in conjugated polymer

FRET-based dynamic structural biology: Challenges, perspectives and an appeal for open-science practices.

Single-molecule FRET (smFRET) has become a mainstream technique for studying biomolecular structural dynamics. The rapid and wide adoption of smFRET experiments by an ever-increasing number of groups has generated significant progress in sample preparation, measurement procedures, data analysis, algorithms and documentation. Several labs that employ smFRET approaches have joined forces to inform the smFRET community about streamlining how to perform experiments and analyze results for obtaining quantitative information on biomolecular structure and dynamics. The recent efforts include blind tests to assess the accuracy and the precision of smFRET experiments among different labs using various procedures. These multi-lab studies have led to the development of smFRET procedures and documentation, which are important when submitting entries into the archiving system for integrative structure models, PDB-Dev. This position paper describes the current 'state of the art' from different perspectives, points to unresolved methodological issues for quantitative structural studies, provides a set of 'soft recommendations' about which an emerging consensus exists, and lists openly available resources for newcomers and seasoned practitioners. To make further progress, we strongly encourage 'open science' practices

FRET-based dynamic structural biology: Challenges, perspectives and an appeal for open-science practices

Single-molecule FRET (smFRET) has become a mainstream technique for studying biomolecular structural dynamics. The rapid and wide adoption of smFRET experiments by an ever-increasing number of groups has generated significant progress in sample preparation, measurement procedures, data analysis, algorithms and documentation. Several labs that employ smFRET approaches have joined forces to inform the smFRET community about streamlining how to perform experiments and analyze results for obtaining quantitative information on biomolecular structure and dynamics. The recent efforts include blind tests to assess the accuracy and the precision of smFRET experiments among different labs using various procedures. These multi-lab studies have led to the development of smFRET procedures and documentation, which are important when submitting entries into the archiving system for integrative structure models, PDB-Dev. This position paper describes the current 'state of the art' from different perspectives, points to unresolved methodological issues for quantitative structural studies, provides a set of 'soft recommendations' about which an emerging consensus exists, and lists openly available resources for newcomers and seasoned practitioners. To make further progress, we strongly encourage 'open science' practices