Microwave-assisted synthesis of thiophene fluorophores, labeling and multilabeling of monoclonal antibodies, and long lasting staining of fixed cells

Exploring the ultrafast and isomer-dependent photodissociation of iodothiophenes via site-selective ionization

C-I bond extension and fission following ultraviolet (UV, 262 nm) photoexcitation of 2- and 3-iodothiophene is studied using ultrafast time-resolved extreme ultraviolet (XUV) ionization in conjunction with velocity map ion imaging. The photoexcited molecules and eventual I atom products are probed by site-selective ionization at the I 4d edge using intense XUV pulses, which induce multiple charges initially localized to the iodine atom. At C-I separations below the critical distance for charge transfer (CT), charge can redistribute around the molecule leading to Coulomb explosion and charged fragments with high kinetic energy. At greater C-I separations, beyond the critical distance, CT is no longer possible and the measured kinetic energies of the charged iodine atoms report on the neutral dissociation process. The time and momentum resolved measurements allow determination of the timescales and the respective product momentum and kinetic energy distributions for both isomers, which are interpreted in terms of rival 'direct' and 'indirect' dissociation pathways. The measurements are compared with a classical over the barrier model, which reveals that the onset of the indirect dissociation process is delayed by ∼1 ps relative to the direct process. The kinetics of the two processes show no discernible difference between the two parent isomers, but the branching between the direct and indirect dissociation channels and the respective product momentum distributions show isomer dependencies. The greater relative yield of indirect dissociation products from 262 nm photolysis of 3-iodothiophene (cf. 2-iodothiophene) is attributed to the different partial cross-sections for (ring-centred) π∗ ← π and (C-I bond localized) σ∗ ← (n/π) excitation in the respective parent isomers.

Vibronic coupling and ultrafast relaxation dynamics in the first five excited singlet electronic states of bithiophene

The vibronic structure and nuclear dynamics in the first five excited singlet electronic states of bithiophene (2T) are investigated here. Specifically, considerations are given to comprehend the first two structureless and broad electronic absorption bands and the role of nonadiabatic coupling in the excited state relaxation mechanism of 2T in the gas phase. Associated potential energy surfaces (PESs) are established by constructing a model vibronic coupling Hamiltonian using 18 vibrational degrees of freedom and extensive ab initio electronic structure calculations. The topographies of these PESs are critically examined, and multiple conical intersections are established. The nuclear dynamics calculations are performed by propagating wave packets on the coupled electronic manifold. The present theoretical results are in good agreement with the experimental observations. It is found that strong nonadiabatic coupling between the S1-S4 and S1-S5 states along totally symmetric modes is predominantly responsible for the structureless and broad first absorption band, and overlapping S2, S3, S4, and S5 states form the second absorption band. Photorelaxation from the highly excited S5 to the lowest S1 state takes place through a cascade of diabatic population transfers among the S1-S4-S5 electronic manifold within the first ∼100 fs. Totally symmetric C=C stretching, C-S stretching, C-H wagging, ring puckering, and inter-ring bending modes collectively drive such relaxation dynamics.

3,4-Ethylenedioxythiophene (EDOT) End-Group Functionalized Poly-ε-caprolactone (PCL): Self-Assembly in Organic Solvents and Its Coincidentally Observed Peculiar Behavior in Thin Film and Protonated Media

End-group functionalization of homopolymers is a valuable way to produce high-fidelity nanostructured and functional soft materials when the structures obtained have the capacity for self-assembly (SA) encoded in their structural details. Herein, an end-functionalized PCL with a π-conjugated EDOT moiety, (EDOT-PCL), designed exclusively from hydrophobic domains, as a functional "hydrophobic amphiphile", was synthesized in the bulk ROP of ε-caprolactone. The experimental results obtained by spectroscopic methods, including NMR, UV-vis, and fluorescence, using DLS and by AFM, confirm that in solvents with extremely different polarities (chloroform and acetonitrile), EDOT-PCL presents an interaction- and structure-based bias, which is strong and selective enough to exert control over supramolecular packing, both in dispersions and in the film state. This leads to the diversity of SA structures, including spheroidal, straight, and helical rods, as well as orthorhombic single crystals, with solvent-dependent shapes and sizes, confirming that EDOT-PCL behaves as a "block-molecule". According to the results from AFM imaging, an unexpected transformation of micelle-type nanostructures into single 2D lamellar crystals, through breakout crystallization, took place by simple acetonitrile evaporation during the formation of the film on the mica support at room temperature. Moreover, EDOT-PCL's propensity for spontaneous oxidant-free oligomerization in acidic media was proposed as a presumptive answer for the unexpected appearance of blue color during its dissolution in CDCl3 at a high concentration. FT-IR, UV-vis, and fluorescence techniques were used to support this claim. Besides being intriguing and unforeseen, the experimental findings concerning EDOT-PCL have raised new and interesting questions that deserve to be addressed in future research.

Human Serum Albumin-Oligothiophene Bioconjugate: A Phototheranostic Platform for Localized Killing of Cancer Cells by Precise Light Activation

The electronic, optical, and redox properties of thiophene-based materials have made them pivotal in nanoscience and nanotechnology. However, the exploitation of oligothiophenes in photodynamic therapy is hindered by their intrinsic hydrophobicity that lowers their biocompatibility and availability in water environments. Here, we developed human serum albumin (HSA)-oligothiophene bioconjugates that afford the use of insoluble oligothiophenes in physiological environments. UV-vis and electrophoresis proved the conjugation of the oligothiophene sensitizers to the protein. The bioconjugate is water-soluble and biocompatible, does not have any "dark toxicity", and preserves HSA in the physiological monomeric form, as confirmed by dynamic light scattering and circular dichroism measurements. In contrast, upon irradiation with ultralow light doses, the bioconjugate efficiently produces reactive oxygen species (ROS) and leads to the complete eradication of cancer cells. Real-time monitoring of the photokilling activity of the HSA-oligothiophene bioconjugate shows that living cells "explode" upon irradiation. Photodependent and dose-dependent apoptosis is one of the primary mechanisms of cell death activated by bioconjugate irradiation. The bioconjugate is a novel theranostic platform able to generate ROS intracellularly and provide imaging through the fluorescence of the oligothiophene. It is also a real-time self-reporting system able to monitor the apoptotic process. The induced phototoxicity is strongly confined to the irradiated region, showing localized killing of cancer cells by precise light activation of the bioconjugate.

Structural Similarities between Some Common Fluorophores Used in Biology, Marketed Drugs, Endogenous Metabolites, and Natural Products

It is known that at least some fluorophores can act as 'surrogate' substrates for solute carriers (SLCs) involved in pharmaceutical drug uptake, and this promiscuity is taken to reflect at least a certain structural similarity. As part of a comprehensive study seeking the 'natural' substrates of 'orphan' transporters that also serve to take up pharmaceutical drugs into cells, we have noted that many drugs bear structural similarities to natural products. A cursory inspection of common fluorophores indicates that they too are surprisingly 'drug-like', and they also enter at least some cells. Some are also known to be substrates of efflux transporters. Consequently, we sought to assess the structural similarity of common fluorophores to marketed drugs, endogenous mammalian metabolites, and natural products. We used a set of some 150 fluorophores along with standard fingerprinting methods and the Tanimoto similarity metric. Results: The great majority of fluorophores tested exhibited significant similarity (Tanimoto similarity > 0.75) to at least one drug, as judged via descriptor properties (especially their aromaticity, for identifiable reasons that we explain), by molecular fingerprints, by visual inspection, and via the "quantitative estimate of drug likeness" technique. It is concluded that this set of fluorophores does overlap with a significant part of both the drug space and natural products space. Consequently, fluorophores do indeed offer a much wider opportunity than had possibly been realised to be used as surrogate uptake molecules in the competitive or trans-stimulation assay of membrane transporter activities.

Designer Fluorescent Adenines Enable Real-Time Monitoring of MUTYH Activity

The human DNA base excision repair enzyme MUTYH (MutY homolog DNA glycosylase) excises undamaged adenine that has been misincorporated opposite the oxidatively damaged 8-oxoG, preventing transversion mutations and serving as an important defense against the deleterious effects of this damage. Mutations in the MUTYH gene predispose patients to MUTYH-associated polyposis and colorectal cancer, and MUTYH expression has been documented as a biomarker for pancreatic cancer. Measuring MUTYH activity is therefore critical for evaluating and diagnosing disease states as well as for testing this enzyme as a potential therapeutic target. However, current methods for measuring MUTYH activity rely on indirect electrophoresis and radioactivity assays, which are difficult to implement in biological and clinical settings. Herein, we synthesize and identify novel fluorescent adenine derivatives that can act as direct substrates for excision by MUTYH as well as bacterial MutY. When incorporated into synthetic DNAs, the resulting fluorescently modified adenine-release turn-on (FMART) probes report on enzymatic base excision activity in real time, both in vitro and in mammalian cells and human blood. We also employ the probes to identify several promising small-molecule modulators of MUTYH by employing FMART probes for in vitro screening.

The Effect of New Thiophene-Derived Diphenyl Aminophosphonates on Growth of Terrestrial Plants

The aim of this work was to evaluate the impact of the thiophene-derived aminophosphonates 1–6 on seedling emergence and growth of monocotyledonous oat (Avena sativa) and dicotyledonous radish (Raphanus sativus L.), and phytotoxicity against three persistent and resistant weeds (Galinsoga parviflora Cav., Rumex acetosa L., and Chenopodium album). Aminophosphonates 1–6 have never been described in the literature. The phytotoxicity of tested aminophosphonates toward their potential application as soil-applied herbicides was evaluated according to the OECD (Organization for Economic and Cooperation Development Publishing) 208 Guideline. In addition, their ecotoxicological impact on crustaceans Heterocypris incongruens and bacteria Aliivibrio fischeri was measured using the OSTRACODTOXKIT^TM and Microtox^® tests. Obtained results showed that none of the tested compounds were found sufficiently phytotoxic and none of them have any herbicidal potential. None of the tested compounds showed important toxicity against Aliivibrio fischeri but they should be considered as slightly harmful. Harmful impacts of compounds 1–6 on Heterocypris incongruens were found to be significant.

Ring-opening/annulation reaction of cyclopropyl ethanols: concise access to thiophene aldehydes via C–S bond formation

The synthesis of thiophene aldehydes from easily available cyclopropyl ethanol derivatives and potassium sulfide has been developed.

Labeling Single Domain Antibody Fragments with Fluorine-18 Using 2,3,5,6-Tetrafluorophenyl 6-[18F]Fluoronicotinate Resulting in High Tumor-to-Kidney Ratios

ImmunoPET agents are being investigated to assess the status of epidermal growth factor receptor 2 (HER2) in breast cancer patients with the goal of selecting those likely to benefit from HER2-targeted therapies and monitoring their progress after these treatments. We have been exploring the use of single domain antibody fragments (sdAbs) labeled with ¹⁸F using residualizing prosthetic agents for this purpose. In this study, we have labeled two sdAbs that bind to different domains on the HER2 receptor, 2Rs15d and 5F7, using 2,3,5,6-tetrafluorophenyl 6-[¹⁸F]fluoronicotinate ([¹⁸F]TFPFN) and evaluated their HER2 targeting properties in vitro and in vivo. The overall decay-corrected radiochemical yield for the synthesis of [¹⁸F]TFPFN-2Rs15d and [¹⁸F]TFPFN-5F7 was 5.7 ± 3.6 and 4.0 ± 2.0%, respectively. The radiochemical purity of labeled sdAbs was >95%, immunoreactive fractions were about 60%, and affinity was in the low nanomolar range. Intracellularly trapped activity from [¹⁸F]TFPFN-2Rs15d and [¹⁸F]TFPFN-5F7 in HER2-expressing SKOV-3 ovarian and BT474M1 breast carcinoma cells were similar to the sdAbs labeled using the previously validated radioiodination residualizing prosthetic agents N-succinimidyl 4-guanidinomethyl-3-[¹²⁵I]iodobenzoate ([¹²⁵I]SGMIB) and N-succinimidyl 3-guanidinomethyl-5-[¹²⁵I]iodobenzoate ( iso-[¹²⁵I]SGMIB). Intracellular activity was about 2-fold higher for radiolabeled 5F7 compared with 2Rs15d for both ¹⁸F and ¹²⁵I. While tumor uptake of both [¹⁸F]TFPFN-2Rs15d and [¹⁸F]TFPFN-5F7 was comparable to those for the coadministered ¹²⁵I-labeled sdAb, renal uptake of the ¹⁸F-labeled sdAbs was substantially lower. In microPET images, the tumor was clearly delineated in SKOV-3 and BT474 xenograft-bearing athymic mice with low levels of background activity in normal tissues, except the bladder. These results indicate that the [¹⁸F]TFPFN prosthetic group could be a valuable reagent for developing sdAb-based immunoPET imaging agents.

The evolution of artificial light actuators in living systems: from planar to nanostructured interfaces

Artificially enhancing light sensitivity in living cells allows control of neuronal paths or vital functions avoiding the wiring associated with the use of stimulation electrodes. Many possible strategies can be adopted for reaching this goal, including the direct photoexcitation of biological matter, the genetic modification of cells or the use of opto-bio interfaces. In this review we describe different light actuators based on both inorganic and organic semiconductors, from planar abiotic/biotic interfaces to nanoparticles, that allow transduction of a light signal into a signal which in turn affects the biological activity of the hosting system. In particular, we will focus on the application of thiophene-based materials which, thanks to their unique chemical-physical properties, geometrical adaptability, great biocompatibility and stability, have allowed the development of a new generation of fully organic light actuators for in vivo applications.

Thiophene bridged aldehydes (TBAs) image ALDH activity in cells via modulation of intramolecular charge transfer

Aldehyde dehydrogenases (ALDHs) catalyze the oxidation of an aldehyde to a carboxylic acid and are implicated in the etiology of numerous diseases. However, despite their importance, imaging ALDH activity in cells is challenging due to a lack of fluorescent imaging probes. In this report, we present a new family of fluorescent probes composed of an oligothiophene flanked by an aldehyde and an electron donor, termed thiophene-bridged aldehydes (TBAs), which can image ALDH activity in cells. The TBAs image ALDH activity via a fluorescence sensing mechanism based on the modulation of intramolecular charge transfer (ICT) and this enables the TBAs and their ALDH-mediated oxidized products, thiophene-bridged carboxylates (TBCs), to have distinguishable fluorescence spectra. Herein, we show that the TBAs can image ALDH activity in cells via fluorescence microscopy, flow cytometry, and in a plate reader. Using TBA we were able to develop a cell-based high throughput assay for ALDH inhibitors, for the first time, and screened a large, 1460-entry electrophile library against A549 cells. We identified α,β-substituted acrylamides as potent electrophile fragments that can inhibit ALDH activity in cells. These inhibitors sensitized drug-resistant glioblastoma cells to the FDA approved anti-cancer drug, temozolomide. The TBAs have the potential to make the analysis of ALDH activity in cells routinely possible given their ability to spectrally distinguish between an aldehyde and a carboxylic acid.

Cationic Polythiophenes as Gene Delivery Enhancer

There is urgent demand of easily available and highly effective method to improve transgene performance of polymeric gene carriers at low consumption of delivery materials. We developed biocompatible multicomponent nanocomposites in which small quantities of cationic polythiophenes were engineered into the outer shell of polypeptide/DNA polyplexes without covalent linkages. We revealed the introduction of polythiophenes in small quantities led to multiple outcomes including modulation of polyplex size and zeta potential, increase in polyplex stability, promotion of endolysosome membrane disruption, light-induced generation of reactive oxygen species (ROS), and significant enhancement of gene delivery to tumor cells. The factors such as structural architectures, molecular weights, photosensitizing capability, and percentage composition of polythiophenes were investigated.

Ab initio molecular dynamics of thiophene: the interplay of internal conversion and intersystem crossing

Ab initio on-the-fly molecular dynamics reveals that excited thiophene decays via low lying conical intersections and via intersystem crossing. Open-ring structures are responsible for the observed long life times.

Deactivation pathways of thiophene and oligothiophenes: internal conversion versus intersystem crossing

Quantum chemical calculations reveal that excited thiophene decays via a low lying conical intersection seam. In oligothiophenes barriers inhibit this passage while deactivation pathways via intersystem crossing channels open.

New biocompatible polymeric micelles designed for efficient intracellular uptake and delivery

New amphiphilic block copolymers are easily synthesised by post-polymerisation modifications of poly(glycidyl methacrylate) chain derivatives. The obtained material, upon dispersion in water, is capable of self-assembling into robust micelles. These nanoparticles, which are also characterised by adaptable stability, were loaded with different thiophene based fluorophores. The photoluminescent micelles were administered to cultured cells revealing a high and rapid internalisation of structurally different fluorescent molecules by the same internalisation pathway. Appropriate pairs of chromophores were selected and loaded into the micelles to induce Förster resonance energy transfer (FRET). The disappearing of the FRET phenomenon, after cell uptaking, demonstrated the intracellular release of the nanoparticle contents. The studied nanomaterial and the loaded chromophores have also shown to be biocompatible and non toxic towards the tested cells.

Supramolecular oligothiophene microfibers spontaneously assembled on surfaces or coassembled with proteins inside live cells

During the last few decades, multifunctional nano- and microfibers made of semiconducting π-conjugated oligomers and polymers have generated much interest because of a broad range of applications extending from sensing to bioelectronic devices and (opto)electronics. The simplest technique for the fabrication of these anisotropic supramolecular structures is to let the molecules do the work by spontaneous organization driven by the information encoded in their molecular structure. Oligothiophenes-semiconducting and fluorescent compounds that have been extensively investigated for applications in thin-film field-effect transistors and solar cells and to a lesser extent as dyes for fluorescent labeling of proteins, DNA, and live cells-are particularly suited as building blocks for supramolecular architectures because of the peculiar properties of the thiophene ring. Because of the great polarizability of sulfur outer-shell electrons and the consequent facile geometric deformability and adaptability of the ring to the environment, thiophene can generate multiple nonbonding interactions to promote non-covalent connections between blocks. Furthermore, sulfur can be hypervalent, i.e., it can accommodate more than the eight electrons normally associated with s and p shells. Hypervalent oligothiophene-S,S-dioxides whose oxygen atoms can be involved in hydrogen bonding have been synthesized. These compounds are amphiphilic, and some of them are able to spontaneously cross the membrane of live cells. Hypervalent nonbonding interactions of divalent sulfur, defined as weak coordination to a proximate nitrogen or oxygen, have also been invoked in the solid-state packing of many organic molecules and in the architecture of proteins. In this Account, we describe two different types of thiophene-based building blocks that can induce the spontaneous formation of nanostructured microfibers in very different environments. The first, based on the synthesis of "sulfur-overrich" hexamers and octamers, leads to surface-independent self-assembly of microfibers-helical or rodlike depending on the groups attached to the same identical inner core-that are crystalline, fluorescent, and conductive and display chirality despite the lack of chiral carbon atoms on the building blocks. Supramolecular polymorphic microfibers are also formed, and they are characterized by very different functional properties. The second, based on a rigid oligothiophene-S,S-dioxide, leads to coassembled protein-oligothiophene microfibers that are physiologically formed inside live cells. The oligothiophene-S,S-dioxide can indeed spontaneously cross the membrane of live cells and be directed toward the perinuclear region, where it is recognized and incorporated by specific peptides during the formation of fibrillar proteins without being harmful to the cells. Coassembled oligothiophene-protein microfibers are progressively formed through a cell-mediated physiological process. Thanks to the oligothiophene blocks, the microfibers possess fluorescence and charge-conduction properties. By means of fluorescence imaging, we demonstrated that various types of live cells seeded on these microfibers were able to internalize and degrade them, experiencing in turn different effects on their morphology and viability, suggesting a possible use of the microfibers as multiscale biomaterials to direct cell behavior. On the whole, our results show the great versatility of oligothiophene building blocks and allow us to foresee that their capabilities of spontaneous assembly in the most different environments could be exploited in much more exciting research fields than those explored to date.

Fluorescent thiophene-based materials and their outlook for emissive applications

An overview of fluorescent thiophene-based materials and their applications, highlighting in particular the various methods employed to achieve highly emissive materials.

The geometry relaxation and intersystem crossing of quaterthiophene studied by femtosecond spectroscopy

The geometry relaxation in the singlet state and the intersystem crossing from relaxed singlet to triplet state are 70 and 398 ps, respectively.

Live cell cytoplasm staining and selective labeling of intracellular proteins by non-toxic cell-permeant thiophene fluorophores

A structurally correlated series of cell-permeant thiophene fluorophores, characterized by intense green or red fluorescence inside live mouse embryonic fibroblasts, was developed. The fluorophores displayed rapid internalization, excellent retention inside the cells, and high optical stability in the cytosolic environment and did not alter cell viability and reproducibility. Depending on the molecular structure, they experienced distinct fate inside the cells: from bright and lasting staining of the cytoplasm to selective tagging of a small set of globular proteins.

Planarizable push–pull oligothiophenes: in search of the perfect twist

The “twistome” of push–pull oligothiophenes is covered comprehensively. Particular emphasis is on the development of conceptually innovative fluorescent membrane probes.

The structural basis for optimal performance of oligothiophene-based fluorescent amyloid ligands: conformational flexibility is essential for spectral assignment of a diversity of protein aggregates

Protein misfolding diseases are characterized by deposition of protein aggregates, and optical ligands for molecular characterization of these disease-associated structures are important for understanding their potential role in the pathogenesis of the disease. Luminescent conjugated oligothiophenes (LCOs) have proven useful for optical identification of a broader subset of disease-associated protein aggregates than conventional ligands, such as thioflavin T and Congo red. Herein, the molecular requirements for achieving LCOs able to detect nonthioflavinophilic Aβ aggregates or non-congophilic prion aggregates, as well as spectrally discriminate Aβ and tau aggregates, were investigated. An anionic pentameric LCO was subjected to chemical engineering by: 1) replacing thiophene units with selenophene or phenylene moieties, or 2) alternating the anionic substituents along the thiophene backbone. In addition, two asymmetric tetrameric ligands were generated. Overall, the results from this study identified conformational freedom and extended conjugation of the conjugated backbone as crucial determinants for obtaining superior thiophene-based optical ligands for sensitive detection and spectral assignment of disease-associated protein aggregates.

3,4-Ethylenedioxythiophene in planarizable push-pull oligothiophenes

We report design, synthesis and evaluation of push-pull quaterthiophene amphiphiles containing one 3,4-ethylenedioxythiophene (EDOT) and a single strong twist in the scaffold. Planarizable push-pull oligothiophene amphiphiles have been introduced recently as conceptually innovative fluorescent probes that sense the fluidity and the potential of lipid bilayer membranes. The "hyper-twisted" EDOT probes respond to planarization and restricted rotational freedom with a red shift and changes in vibrational finestructure in the excitation spectrum, respectively. In solution, comparably weak solvatochromism and significant thermochromism are found. Planarization and restricted rotational freedom afford exquisite sensitivity toward nature and fluidity of lipid bilayer membranes, including ratiometric detection of phase transitions. The sensing of membrane potentials is weakened by these unique properties but remains possible.

Optical properties of hybrid T3Pyr/SiO2/3C-SiC nanowires

A new class of nanostructured hybrid materials is developed by direct grafting of a model thiophene-based organic dye on the surface of 3C-SiC/SiO2 core/shell nanowires. TEM-EDX analysis reveals that the carbon distribution is more spread than it would be, considering only the SiC core size, suggesting a main contribution from C of the oligothiophene framework. Further, the sulfur signal found along the treated wires is not detected in the as-grown samples. In addition, the fluorescent spectra are similar for the functionalized nanostructures and T3Pyr in solution, confirming homogeneous molecule grafting on the nanowire surface. Chemical and luminescence characterizations confirm a homogeneous functionalization of the nanowires. In particular, the fluorophore retains its optical properties after functionalization.

pH controlled staining of CD4(+) and CD19(+) cells within functionalized microfluidic channel

Herein proposed is a simple system to realize hands-free labeling and simultaneous detection of two human cell lines within a microfluidic device. This system was realized by novel covalent immobilization of pH-responsive poly(methacrylic acid) microgels onto the inner glass surface of an assembled polydimethylsiloxane/glass microfluidic channel. Afterwards, selected thiophene labeled monoclonal antibodies, specific for recognition of CD4 antigens on T helper/inducer cells and CD19 antigens on B lymphocytes cell lines, were encapsulated in their active state by the immobilized microgels. When the lymphocytes suspension, containing the two target subpopulations, was flowed through the microchannel, the physiological pH of the cellular suspension induced the release of the labeled antibodies from the microgels and thus the selective cellular staining. The selective pH-triggered staining of the CD4- and CD19-positive cells was investigated in this preliminary experimental study by laser scanning confocal microscopy. This approach represents an interesting and versatile tool to realize cellular staining in a defined module of lab-on-a-chip devices for subsequent detection and counting.

α,ω-Dihexylsexithiophene self-assembled nanostructures on mica: atomic force microscopy study

Self-assembled nanostructures of α,ω-dihexylsexithiophene (DH6T) formed by spreading DH6T solutions onto freshly cleaved mica surface were studied by atomic force microscopy. The effects of solvent and concentration on the nanostructures of DH6T molecules were studied. Flat, well-ordered, and platelet-like domains were observed on mica surfaces after treatment with various polar solvent solutions of DH6T. These domains form a uniform film with height of 2.4 ± 0.2 nm, which is consistent with a 45° tilt in the molecular conformation of DH6T on mica surfaces. The formation mechanism of these multilayers is discussed in detail.

Oligothiophenes as fluorescent markers for biological applications

This paper summarizes some of our results on the application of oligothiophenes as fluorescent markers for biological studies. The oligomers of thiophene, widely known for their semiconductor properties in organic electronics, are also fluorescent compounds characterized by chemical and optical stability, high absorbance and quantum yield. Their fluorescent emission can be easily modulated via organic synthesis by changing the number of thiophene rings and the nature of side-chains. This review shows how oligothiophenes can be derivatized with active groups such as phosphoramidite, N-hydroxysuccinimidyl and 4-sulfotetrafluorophenyl esters, isothiocyanate and azide by which the (bio)molecules of interest can be covalently bound. This paper also describes how molecules such as oligonucleotides, proteins and even nanoparticles, tagged with oligothiophenes, can be used in experiments ranging from hybridization studies to imaging of fixed and living cells. Finally, a few multilabeling experiments are described.