Palladium‐Mediated Surface‐Initiated Kumada Catalyst Polycondensation: A Facile Route Towards Oriented Conjugated Polymers

Palladium‐mediated surface‐initiated Kumada catalyst transfer polycondensation is used to generate poly(3‐methyl thiophene) films with controlled thickness up to 100 nm. The palladium initiator density is measured using cyclic voltammetry and a ferrocene‐capping agent, where the surface density is found to be 55% (1.1 × 10¹⁴ molecules per cm²). UV–Vis spectroscopy and AFM show increased aggregation in palladium‐initiated films due to the higher grafting density of palladium initiators on the surface. The anisotropy of the P3MT films is determined using polarized UV–Vis spectroscopy, which indicates a degree of orientation perpendicular to the substrate. Evidence that palladium can maintain π‐complexation even at elevated temperatures, is also shown through the exclusive intramolecular coupling of both a phenyl and thiophene‐based magnesium bromide with different dihaloarenes.     

Kumada Catalyst‐Transfer Polycondensation: Mechanism,Opportunities, and Challenges

Kumada catalyst‐transfer polycondensation (KCTP) is a new but rapidly developing method with great potential for the preparation of well‐defined conjugated polymers (CPs). The recently discovered chain‐growth mechanism is unique among the various transition metal‐catalyzed polycondensations, and has thus attracted much attention among researchers. Most progress is found in the areas of mechanism and external initiation via new initiators, but also the number of monomers other than thiophene that can be polymerized is steadily increasing. Accordingly, the variety of CP chain architectures is increasing as well, and a considerable contribution of KCTP toward more efficient materials can be expected in the future. This review critically focuses on very recent progress in the synthesis of CPs and the mechanism of KCTP, and is finally aimed at providing a comprehensive picture of this exciting polymerization method.

     

Combinatorial Energy Transfer between an End‐Capped Conjugated Polyelectrolyte and Chromophore‐Labeled PNA for Strand‐Specific DNA Detection

We report a macromolecular end‐capping approach to improve the detection sensitivity of cationic conjugated polymer (CCP) based DNA detection. A phenylethynyl anthracene (PEA) end‐capped cationic polyfluorene (PF) derivative ( P1 ) is synthesized via Suzuki coupling. Due to efficient fluorescence resonance energy transfer (FRET) from the polymer backbone to the end‐capper PEA units, the polymer ( P1 ) fluorescence is dominated by the emission from PEA even in dilute aqueous solution. P1 emission has a better spectral overlap with fluorescein (Fl) absorption compared to that for uncapped PF ( P2 ). In addition, the intra and intermolecular energy transfer for P1 is more efficient in the presence of DNA due to complexation‐induced polymer aggregation. These impart a combinatorial FRET between P1 and an Fl‐labeled probe which is more efficient than that between P2 and the same probe. P1 thus offers a better DNA detection sensitivity relative to P2 and opens up new opportunities to improve the performance of CCP based biosensors involving FRET.

     

Cobalt Ion‐Mediated Cysteine Detection With a Hyperbranched Conjugated Polyelectrolyte as a New Sensing Platform

A highly efficient colorimetric and fluorescence turn‐off probe for the sensitive and selective detection of the biologically important amino acid, cysteine (Cys), is demonstrated using a newly synthesized water‐soluble hyperbranched polymer (HP) containing sulfonic acid groups. The detection mechanism involves two steps: (i) the slight quenching of HP in the presence of Co²⁺ in advance; and (ii) the gradual quenching of the HP–Co²⁺ complex according to the concentration of Cys due to the absorption screening effect of the formation of the Cys‐Co²⁺ complex, which prevents HP from absorbing excitation energy.     

A Micellar Complex of a Conjugated Polyelectrolyte for Efficient FRET to Dye‐Labeled DNA

A polymer–surfactant micellar complex has been studied as a fluorescence resonance energy transfer (FRET) donor to fluorescein‐labeled DNA (ssDNA‐Fl). In water, the molar absorptivity and fluorescence quantum efficiency of cationic poly(fluorene‐co‐phenylene) (c‐PFP) are substantially increased in the presence of non‐ionic surfactants. A TEM microscopic study shows the formation of a nanowire micellar complex of c‐PFP and the surfactants. About a 400% enhancement of the FRET signal is measured in c‐PFP/ssDNA‐Fl with Brij 30, relative to that without surfactants. The signal amplification is successfully modulated using different types of non‐ionic surfactants which perturb the complexation, fine‐structure of the complex (i.e., donor‐acceptor separation), and the resulting energy transfer process.

     

Surface‐Grafted conjugated polymers for hybrid cellulose materials

Conjugated polymers were grafted onto cellulose substrates in an effort to create a general method for the synthesis of conjugated polymer/cellulose hybrid materials. In this report, we describe the grafting of poly(fluorene), poly(fluorenevinylene), and a poly(fluorene‐ethynylene‐phenylene) onto modified cellulose paper substrates using Suzuki, Heck, and Sonogashira‐type polymerizations, respectively. The application of these three widely used coupling chemistries to surface‐grafted conjugated polymers on cellulose provides a general route to cellulose‐based hybrid materials tunable with almost any aromatic repeat structure for specific applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Excitation Energy Transfer from Semi‐Conducting Polymer Nanoparticles to Surface‐Bound Fluorescent Dyes

Summary: The first examples of the dye‐coated semi‐conducting polymer nanoparticles as well as experiments to demonstrate the excitation energy transfer from the excited chromophor of the nanoparticle to the fluorescent dye are described. We have demonstrated that the blue fluorescence of the dye‐coated polyfluorene nanoparticles is only slightly quenched after dye deposition. However, a new emission band of the surface‐bound dye (Rhodamine 6G or Rhodamine TM) appears in the wavelength region of 530–600 nm. These results clearly indicate an effective excitation energy transfer from the excited PF chromophores to the fluorescent dye.

Emission spectra of PF2/6 nanoparticle dispersion and of Rhodamine 6G‐coated nanoparticle dispersion.     

Synthesis of diketopyrrolopyrrole‐containing conjugated polyelectrolytes for naked‐eye detection of DNA

Two water‐soluble cationic conjugated polyelectrolytes ( P1 and P2 ) containing diacetylene, diketopyrrolopyrrole (DPP), and fluorene units were synthesized with Glaser‐Hay coupling reaction as the key step. The narrow bandgap DPP units and the wide bandgap fluorene units in the cationic polyelectrolytes might form an energy donor‐acceptor molecule architectures, in which DPP units serve as an acceptor of the fluorescent resonance energy transfer. The addition of calf thymus DNA enhances the fluorescent resonance energy transfer from fluoreneethynylene segments to DPP units, which results in a sensitive color change from blue to red in the PL spectra and allows naked‐eye detection of DNA with low concentration. In addition, the detection of DNA with P1 and P2 is high selective because it is not interfered by common ions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Alternating Intramolecular and Intermolecular Catalyst‐Transfer Suzuki–Miyaura Condensation Polymerization: Synthesis of Boronate‐Terminated π‐Conjugated Polymers Using Excess Dibromo Monomers

The Suzuki–Miyaura coupling polymerization of dibromoarene 1 and arylenediboronic acid (ester) 2 with a Pd catalyst having a high propensity for intramolecular catalyst transfer is reported. The polymerization of excess 1 with 2 affords high‐molecular‐weight π‐conjugated polymer having boronic acid (ester) moieties at both ends, contrary to Flory's principle. This unstoichiometric polycondensation behavior is accounted for by intramolecular transfer of the Pd catalyst on 1 . In the polymerization of 1 and 2 having different aryl residues, high‐molecular‐weight polymer is obtained when the stronger donor aromatic is used as the dibromo monomer and the weaker donor or acceptor aromatic is used as diboronic acid (ester) monomer. The pinacol boronate moieties at both ends of the obtained poly(p‐phenylene) (PPP) can be converted to benzoic acid ester, hydroxyl group, and bromine. Furthermore, the reaction of the pinacol boronate‐terminated PPP with poly(3‐hexylthiophene) (P3HT) having bromine at one end yields a triblock copolymer of P3HT‐b‐PPP‐b‐P3HT.

     

Three‐Dimensionally Ordered Macroporous Nitroxide Polymer Brush Electrodes Prepared by Surface‐Initiated Atom Transfer Polymerization for Organic Radical Batteries

The synthesis and electrochemical performance of three‐dimensionally ordered macroporous (3DOM) nitroxide polymer brush electrodes for organic radical batteries are reported. The 3DOM electrodes are synthesized via polystyrene colloidal crystal templating with electropolymerization of polypyrrole, modification of surface initiator, and surface‐initiated atom transfer radical polymerization. The discharge capacity of the 3DOM electrodes is proportional to the thickness of the inverse opal. The discharge capacity of the 3DOM electrode at a discharge rate of 5 C is 40 times higher than that of the planar electrode; its cycle‐life performance exhibits 96.1% retention after 250 cycles.     

A Water‐Soluble Conjugated Polymer for Protein Identification and Denaturation Detection

Rapid and sensitive methods to detect proteins and protein denaturation have become increasingly needful in the field of proteomics, medical diagnostics, and biology. In this paper, we have reported the synthesis of a new cationic water‐soluble conjugated polymer that contains fluorene and diene moieties in the backbone ( PFDE ) for protein identification by sensing an array of PFDE solutions in different ionic strengths using the linear discriminant analysis technique (LDA). The PFDE can form complexes with proteins by electrostatic and/or hydrophobic interactions and exhibits different fluorescence response. Three main factors contribute to the fluorescence response of PFDE , namely, the net charge density on the protein surface, the hydrophobic nature of the protein, and the metalloprotein characteristics. The denaturation of proteins can also be detected using PFDE as a fluorescent probe. The interactions between PFDE and proteins were also studied by dynamic light scattering (DLS) and isothermal titration microcalorimetry (ITC) techniques. In contrast to other methods based on conjugated polymers, the synthesis of a series of quencher or dye‐labeled acceptors or protein substrates has been avoided in our method, which significantly reduces the cost and the synthetic complexity. Our method provides promising applications on protein identification and denaturation detection in a simple, fast, and label‐free manner based on non‐specific interaction‐induced perturbation of PFDE fluorescence response.     

Numerical Self‐Consistent Field Theory of Cylindrical Polyelectrolyte Brushes

A single cylindrical polyelectrolyte brush is studied by self‐consistent field (SCF) theory and the results compared with predictions from scaling theory. It is shown that the SCF theory results give the general trends as well as insight into the crossover regions between different regimes. The density profiles of the polyions and small ions indicate that the systems are locally electroneutral. The salted brush bears characteristics similar to those of a neutral brush. Counter‐intuitively, the chains are not uniformly stretched in the osmotic regime. The free‐end monomers shift to the outer region and an exclusion zone appears and grows with decreasing of salt concentration.

     

Stille Catalyst‐Transfer Polycondensation Using Pd‐PEPPSI‐IPr for High‐Molecular‐Weight Regioregular Poly(3‐hexylthiophene)

A commercially available palladium N‐heterocyclic carbene (Pd‐NHC) precatalyst is used to initiate chain‐growth polymerization of 2‐bromo‐3‐hexyl‐5‐trimethylstannylthiophene. The molecular weight of the resultant poly(3‐hexylthiophene) can be modulated (7 to 73 kDa, Đ = 1.14 to 1.53) by varying the catalyst concentration. Mass spectrometry data confirm control over the polymer end groups and ¹H NMR spectroscopy reveals that the palladium catalyst is capable of “ring‐walking”. A linear relationship between M_n and monomer conversion is observed. Atomic force microscopy and X‐ray scattering verify the regioregular nature of the resultant polythiophene.

     

Assembly of Anionic Conjugated Polymer with 6‐O‐Modified PNP‐β‐Galactoside for Fluorescence Logic‐signal‐based Multiplex Detections of Enzymes

Anionic conjugated polymer (PFP‐SO) was assembled with a novel enzymatic substrate 6‐O‐modified PNP‐β‐galactoside ( 1 ) for sensitive multiplex enzyme detections. The PFP‐SO/ 1 /lipase/β‐galactosidase system has two chemical input signals which are Input 1 (lipase) and Input 2 (β‐galactosidase), and output optical signals such as fluorescence emission at 416 nm or 450 nm. Four types of logic gates, including YES, INH, NAND and AND, were successfully constructed and utilized for multiplex detections of lipase and β‐galactosidase in one tube.

     

Synthesis of molecular‐weight‐controlled polyfluorene with boronate at one end

We investigated the synthesis of polyfluorene with a pinacol boronate (PinB) moiety at one end and with controlled molecular weight by means of Suzuki–Miyaura coupling polymerization of pinacol (7‐bromo‐9,9‐dioctyl‐9H‐fluoren‐2‐yl)boronate ( 1 ) with a palladium(0) precatalyst in the presence of pinacol 4‐trifluoromethylphenylboronate ( 2 ) as a chain terminator and CsF/18‐crown‐6 as a base. When we used AmPhos Pd G2, which has a propensity for intramolecular catalyst transfer on a π‐electron face, polyfluorene with the PinB moiety at one end and PhCF₃ (derived from 2 ) at the other end was obtained, and the molecular weight increased in proportion to the feed ratio of [ 1 ]₀/[catalyst]₀, though the molecular weight distribution was broad. Since the molecular weight also linearly increased with respect to the conversion of 1 until the middle stage of polymerization, the polymerization appears to involve chain‐growth polymerization through intramolecular catalyst transfer from the Pd catalyst inserted into the C? Br bond of 1 . The broad molecular weight distribution might be mainly due to slow initiation and slow termination with 2 , rather than polymer–polymer coupling. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2498–2504