Soluble Π-conjugated Polymers Research Articles

Diketopyrrollopyrrole anchored carbazole-alt-thiophene based Fe3+-coordinated metallopolymer for the selective recognition of ATP

The emissive π-conjugated polymers are attractive candidates as sensory materials for environmentally and biologically relevant species. In this work, we report design and synthesis of carbazole-thiophene based A- alt -B type efficient fluorescent π-conjugated copolymer probe with diketopyrrollopyrrole units through Pd(II)-catalyzed Sonogashira polymerization from the respective monomers. The well-defined and soluble π-conjugated polymer has been characterized by multinuclear NMR spectra as well as tetradetector GPC studies, showing molecular weight (M w ) of 33.1 kDa. The emissive π-conjugated macromolecular probe consisting of the carbazole-thiophene backbone with diketopyrrolopyrrole ( P1 ) anchoring unit shows selectivity toward Fe 3+ ions inducing quenching of the fluorescence by ca. 72%. More interestingly, the resulting P1· Fe 3+ metallopolymer exhibits high sensitivity and selectivity toward adenosine 5′-triphosphate (ATP) over the other representative pyrophosphate anions. Most importantly, the probe discriminates it from adenosine 5′-diphosphate (ADP) and adenosine 5′-monophosphate (AMP), presumably due to the much stronger electrostatic interaction between polymer and ATP than the others. To understand the sensing mechanism, the detailed photophysical and sensing studies have been carried out to understand the insight of metallopolymer-ATP interaction, which is responsible for selective fluorescence enhancing of P1· Fe 3+ metallopolymer. The limit of detection of the metallopolymer probe towards ATP was found to be in the range of 7.92 × 10 −7 M (365 ppb) with a high association constant in the order of 1.96 × 10 5 M −1 . FLIM analysis and the time-resolved fluorescence anisotropy study have also been carried out to investigate molecular interaction between P1· Fe 3+ metallopolymer and ATP. • Design and synthesis of well-defined diketopyrrolopyrrole anchored carbazole-thiophene emissive polymers. • Selective and sensitive turn-off fluorescent probe for Fe 3+ . • Trace and selective detection of ATP in ppb level. • Efficient strategy to develop simple, sensitive and reusable fluorescent probe for biologically relevant species.

Vinylene-versus azomethine-bridged carbazole-based polymers for light emission and sensor applications

Two new carbazole-based soluble π-conjugated polymers were synthetized and investigated: P1 is a poly(p-phenylenevinylene) analogue and P2 is a poly-azomethine-type polymer. The macromolecular structures of P1 and P2 were confirmed by nuclear magnetic resonance and infrared spectroscopies. The effect of vinylene (in P1) and azomethine (in P2) π-linkers on thermal, optical and electrical properties of the two macromolecules was mainly studied. The differential scanning calorimetry and thermogravimetric analyses showed that both polymers are amorphous and better thermal stability was observed in the case of the azomethine containing polymer. The photophysical behavior of these π-conjugated systems were investigated by UV–visible absorption and photoluminescence spectroscopies. Schottky single-layer diodes and Organic Field-Effect Transistors (OFETs) using P1 and P2 as active layers were elaborated in order to study the electrical properties of these polymeric materials. P1 is a semi-conducting and fluorescent polymer, with a yellowish-green emission and a charge carrier mobility of 5.1 10−6 m²/V.s making it a good candidate for organic light emitting devices (OLED) applications. However, the poly-azomethine P2, in its neutral state, is of little interest when compared to the polyvinylene derivative, due to its very low charge transport capacity and negligible fluorescence intensity. We demonstrate in this study that the electrical and optical properties of the poly-azomethine P2 can be dramatically improved by nitrogen protonation of the azomethine linkers. Indeed, under exposure to trifluoroacetic acid (TFA) vapors, an emitted fluorescence that is a linear function of the amount of TFA added to the P2 solution was observed and a charge carrier mobility of 7 10−5 m²/V.s was achieved. This opens the way for these azomethine-containing carbazole-based polymers to promising applications in electrical and fluorescence turn-on sensors.

Direct writing of 3D conjugated polymer micro/nanostructures for organic electronics and bioelectronics

3D direct writing and meniscus-guided pen writing methods, which are capable of fabricating 3D micro/nanostructures from soluble π-conjugated polymers (CPs) and CP precursors, and recent advances in these techniques are addressed in this review.

Poly(benzodithieno-imidazole-alt-carbazole) based π-conjugated copolymers: Highly selective and sensitive turn-off fluorescent probes for Hg2+

In this work, highly emissive and soluble π-conjugated poly(benzodithieno-imidazole-alt-carbazole) π-conjugated copolymers (P1 and P2) have been synthesized through Pd(0)-catalyzed Suzuki coupling polymerization protocol from the corresponding monomers. For solubilizing in common organic solvents, heptyl (in P1) or 2-(2-(2-methoxyethoxy)ethoxy)ethyl (in P2) substituents have been introduced at benzodithieno-imidazole and 9-position of carbazole unit. The well-defined and soluble π-conjugated polymers have been characterized by multinuclear NMR spectra as well as by tetradetector GPC studies showing molecular weight (Mn) of 16.5 and 14.3 kDa with the polydispersity indices of 1.36 and 1.31 respectively. The emissive π-conjugated polymers show remarkable selectivity and sensitivity towards Hg2+ ion as turn-off fluorescent probes as a result of molecular wire effect, without interference by other competing metal ions. The detailed photophysical and sensing studies have been demonstrated to understand the insight of polymer-metal ion interaction which is responsible for selective fluorescence quenching of the π-conjugated polymers. DFT studies have been performed to gain the insight of the electronic properties of the sensor by determining the frontier molecular orbitals and the HOMO-LUMO energy levels for a model probe (M1). The polymeric probes (P1 and P2) are reversible in nature, and can also act as secondary sensors for S2-. The limit of detection of the polymer probes towards Hg2+ is found to be in the range of 40–50 ppb with high association constant in the order of 105 M−1 suggesting its high applicability as chemosensor for Hg2+. The polymers have also been explored as thin film polymeric sensor towards Hg2+ to demonstrate its practical utility.

Synthesis and characterization of 1,2,3-triazole appended polythiophene based reusable fluorescent probe for the efficient detection of trace nitroaromatics

Emissive π-conjugated poly(3-benzyl-1,2,3-triazole thiophene) (P1) and poly(3- benzylthiophene) (P2) have been synthesized via Ni(II)-mediated Grignard metathesis (GRIM) polymerization from the corresponding monomers, 2-bromo-5-iodo-3-benzyl-1,2,3-triazole thiophene (M2) and 2,5-dibromo-3-benzyl thiophene (M3) respectively. The well-defined and soluble π-conjugated polymers have been characterized by multinuclear NMR spectra as well as by tetradetector GPC studies showing molecular weight (Mn) of 19.3 and 17.6 kDa with the polydispersity indices of 1.35 and 1.24 respectively. The synthesized π-conjugated polymers have been explored as fluorescent chemosensor for nitroaromatics (NACs). P1 polymeric probe having 1,2,3-triazole appendage shows the superiority over P2 towards the detection of picric acid vapor as manifested by the fluorescent quenching profile (89% and 41% respectively) due to the facile supramolecular interaction between p-type polymer and electron deficient NACs assisted by the polar 1,2,3-triazolyl unit. To understand the ‘turn-off’ sensing mechanism though photo-induced electron transfer (PET), the detailed photophysical studies have been carried out Furthermore, test paper kits have also been fabricated, showing remarkable trace detection towards picric acid in nano-molar range by naked eye, making it a useful tool for a quick, easy and inexpensive way of detecting NAC explosives.

New soluble π-conjugated polymers containing 2-diisopropylamino-1,3,5-triazine unit: synthesis, characterization and optical properties

A new type of π-conjugated polymers containing 2-diisopropylamino-1,3,5-triazine were prepared via Sonogashira or Suzuki coupling reaction. The structures of the polymers were performed by FT-IR, 1H-NMR, UV–vis spectroscopy, photoluminescence spectroscopy, gel permeation chromatography, thermal analysis and X-ray diffraction analysis. These derived polymers were soluble in common organic solvents such as tetrahydrofuran, chloroform, toluene, and showed good thermal stability. Polymers containing 1,4-diethynyl-2,5-bis(dialkoxy)benzene unit in polymer main chain emitted blue-green light in solution phase under UV light irradiation except with polymer containing 9,9-dioctylfluorene(blue light). Acidochromic behaviors of polymers were studied in CHCl3-CF3COOH mixtures. 9,9-Dioctylfluorene-containing polymer displayed better acidochromic property and linear relationship between absorbance and concentration with the concentration of CF3COOH from 5.384 × 10−4 to 26.92 × 10−4 mol/L. Electrochemical behaviors of polymers depicted p-doping and some hole-transporting properties. XRD results showed that polymers exhibited certain crystallinity.

Synthesis and Electro-Optical Properties of Fluorene-Based Copolymer for Organic Photovoltaic Device Application

The following soluble π-conjugated polymer was synthesized by palladium-catalyzed Suzuki polymerization: poly[(9,9-dioctylfluorene)-alt-(3-hexylthiophen-5-yl)-(4′-hexylthiazol-5′-yl)] poly(FO-HThHTha) derived from poly(9,9-dioctylfluorene) (PFO) and poly[(3-hexylthiophen-5-yl)-2,2′-(4′-hexylthiazol-5′-yl)] poly(HThHTa). The polymer, poly(FO-HThHTa) was soluble in common organic solvents and easily spin coated onto indium-tin oxide (ITO) coated glass substrates. Bulk heterojunction photovoltaic cells with an ITO/PEDOT/poly(FO-HThHTa):PC70BM/TiOx/Al configuration were fabricated and the photovoltaic cell using poly(FO-HThHTa):PC70BM (1:4) showed the best photovoltaic performance compared with those using poly(FO-HThHTa):PC70BM (1:2 and 1:6). The optimal bulk heterojunction photovoltaic cell exhibits a power conversion efficiency (PCE) of 0.39% (Voc = 0.44 V, Jsc = 2.57, FF = 0.34) with poly(FO-HThHTa):PC70BM (1:4) measured by using an AM 1.5 G irradiation (100 mW/cm2) on an Oriel Xenon solar simulator (Oriel 300 W).

π-Conjugated polymers with thermocleavable substituents for use as active layers in organic photovoltaics

The incorporation of tetrahydropyranyl (THP) groups into poly(3-alkylthiophene) offers an opportunity to prepare soluble π-conjugated polymers (πCPs) which, upon thermal annealing, may be rendered insoluble. Recent studies have shown that πCPs that may be rendered insoluble following thin film fabrication have potential use in photovoltaic (PV) applications. Furthermore, inclusion of 3,4-ethylenedioxythiophene (EDOT) into the polymer backbone, which lowers the band gap of the πCPs, provides a system with increased absorption over the solar spectrum. In that regard, the synthesis, absorption profiles, thin film X-ray diffraction and PV properties of poly(3-(6-(2-tetrahydropyranyloxy)hexyl)thiophene), poly(3-(8-(2-tetrahydropyranyloxy)octyl)thiophene) and poly[3,4-ethylenedioxy-3′-(6-(2-tetrahydropyranyloxy)hexyl)-2,2′-bithiophene] are reported herein. In addition to absorption profiles similar to that of poly(3-hexylthiophene) (P3HT), a large degree of order was observed, especially for the octyl derivative; however, upon device fabrication these systems proved to be inferior to that of P3HT:PCBM the current standard for polymeric PVs. This is attributed to a reduction in crystallinity of the conjugated polymer upon: (i) deprotection to the insoluble thin film and (ii) blending with PCBM.

Polymer conformation-assisted wrapping of single-walled carbon nanotube: The impact of cis-vinylene linkage

A soluble π-conjugated polymer cis-P mPV is found to be twice as effective as its trans-P mPV isomer in dispersing SWNTs into organic solvents. The improved efficiency is related to the specific conformation of cis-vinylene-enriched P mPV, which facilitates a planar π–π interaction with SWNT surface and leads to improved nanotube dispersion. 1H NMR spectra indicate that the cis-CH CH bonds are partially converted to the trans-CH CH, thereby providing necessary conformational cavity for SWNT wrapping. Irradiation triggers a precipitation from SWNT dispersion, providing a purified SWNT/conjugated polymer composite.

Molecular Bulk Heterojunctions: An Emerging Approach to Organic Solar Cells

The predicted exhaustion of fossil energy resources and the pressure of environmental constraints are stimulating an intensification of research on renewable energy sources, in particular, on the photovoltaic conversion of solar energy. In this context, organic solar cells are attracting increasing interest that is motivated by the possibility of fabricating large-area, lightweight, and flexible devices using simple techniques with low environmental impact. Organic solar cells are based on a heterojunction resulting from the contact of a donor (D) and an acceptor (A) material. Absorption of solar photons creates excitons, Coulombically bound electron-hole pairs, which diffuse to the D/A interface, where they are dissociated into free holes and electrons by the electric field. D/A heterojunctions can be created with two types of architectures, namely, bilayer heterojunction and bulk heterojunction (BHJ) solar cells. BHJ cells combine the advantages of easier fabrication and higher conversion efficiency due to the considerably extended D/A interface. Until now, the development of BHJ solar cells has been essentially based on the use of soluble pi-conjugated polymers as donor material. Intensive interdisciplinary research carried out in the past 10 years has led to an increase in the conversion efficiency of BHJ cells from 0.10 to more than 5.0%. These investigations have progressively established regioregular poly(3-hexylthiophene) (P3HT) as the standard donor material for BHJ solar cells, owing to a useful combination of optical and charge-transport properties. However, besides the limit imposed to the maximum conversion efficiency by its intrinsic electronic properties, P3HT and more generally polymers pose several problems related to the control of their structure, molecular weight, polydispersity, and purification. In this context, recent years have seen the emergence of an alternative approach based on the replacement of polydisperse polymers by soluble, conjugated single molecules as donor materials in BHJ cells. In fact, molecular donors present specific advantages in terms of structural definition, synthesis, and purification. In this Account, we present a brief survey of recent work in this nascent field of new single-molecule donors in organic solar cells. Various series of three-dimensional donors built by the attachment of different kinds of conjugated branches on a central node, including silicon, twisted bithiophene, triphenylamine, and borondipyrromethene (BODIPY), are discussed in relation to the performances of the resulting solar cells. Furthermore, it is shown that the concept of a molecular donor with internal charge transfer leads at the same time to improved light-harvesting properties, red-shifted photoresponse, and a higher open-circuit voltage, resulting in a considerable increase of conversion efficiency, up to values now approaching 3%. These results show that soluble molecular donors can lead to BHJ cells that combine high conversion efficiency with the distinct advantages of working with single molecules, including structural definition, synthesis, purification, and reproducibility.

Chloro-Nickel and Chloro-Cobalt Complexes Containing Phosphine Ligands: Efficient Initiators for Polymerization of Alkynes

We have developed a new series of single-component air- and moisture-stable catalysts for alkyne polymerization based on chloro-nickel and chloro-cobalt complexes containing phosphine ligands. The polymerization of p-diethynylbenzene initiated by these complexes proceeds smoothly in the presence of amines at room temperature to afford soluble π-conjugated polymers in yields as high as 81% with weight-average molecular weight up to 17 600.

Transition metal acetylide catalysts for polymerization of alkynes: 1. Effect of ligands on catalytic activity of nickel complexes

The catalytic activity of a series of nickel acetylides and chlorides containing different phosphine and alkynyl ligands: NiL 2(CCR) 2; NiL 2(CCR)Cl and NiL 2Cl 2 (L 2=(PPh 3) 2, (PBu 3) 2 and Ph 2PCH 2CH 2PPh 2; R= p-C 6H 4CCH, C 6H 5, H, CH 2OH and CH 2OCOCH 3), towards p-diethynylbenzene polymerization is compared. The catalytic property of these acetylides is related to chlorine, phosphines and alkynyl ligands bonded to the metal atoms. The polarity, steric hindrance and electron-donating ability of ligands are main factors influencing the catalytic activity of these complexes. Nickel acetylides were found to be novel efficient initiating systems for the alkyne polymerization. The polymerization proceeds under mild conditions to give soluble π-conjugated polymers with weight average molecular weights as high as 4.8×10 4 in yields as high as 95%.

Transition metal acetylide catalysts for polymerization of alkynes: 2. Effect of ligands on catalytic activity of palladium complexes

Single-component and environmentally stable palladium acetylides with the structures of PdL 2(CCR) 2 (L=PPh 3, PBu 3; R= p-C 6H 4CCH, C 6H 5, H, CH 2OH, CH 2OCOCH 3, CH 2OCOC 6H 5, CH 2OCOC 6H 4OH- o) are novel efficient initiating systems for p-diethynylbenzene polymerization. The polymerization proceeds under mild conditions to give soluble π-conjugated polymers with molecular weights as high as 1.8×10 4 in yields as high as 84%. The catalytic property of these acetylides is related to phosphine and alkynyl ligands bonded to the metal atoms. Palladium complexes containing PPh 3 ligand are much more active than that containing PBu 3 ligand. The complexes containing polar alkynyl ligands show higher catalytic activity than the corresponding complexes containing non-polar ligands. For the complexes containing non-polar alkynyl ligands, the greater the conjugation degree of the alkynyl ligand, the higher the catalytic activity of the corresponding complex. For the complexes containing polar alkynyl ligands, the complexes containing ester ligands show higher catalytic activity than the corresponding complex containing alcohol ligand, and the catalytic activity of the complexes containing ester ligands increases with increasing acidity of the corresponding acids.

Femtosecond Z-scan and degenerate four-wave mixing measurements of real and imaginary parts of the third-order nonlinearity of soluble conjugated polymers

We investigated the third-order nonlinear optical properties of several soluble π-conjugated polymers with a goal of reliable determination of the parameters that characterize the nonlinearity, such as the real and imaginary parts of the nonlinear refractive index n2 and the one-photon loss and two-photon loss merit factors W and T, respectively. The measurements were performed at 800 nm with 100-fs pulses from an amplified Ti:sapphire system. We present results of investigations of several 2,5-substituted poly(p-phenylene vinylenes), including poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene] and a soluble ladder poly (p-phenylene) polymer. In particular, Z-scan measurements of polymer solutions were found to be useful for the determination of the complex nonlinear refractive index. The results could be verified by time-dependent degenerate four-wave mixing studies performed on thin films of the polymers. We found generally good agreement between the values of n2 determined from Z scan and those from degenerate four-wave mixing. The results indicate that the nonlinear refractive index of the order of 10-12 cm2/W can be readily obtained for various conjugated polymers. However, the two-photon merit factors T larger than unity are commonly encountered within the two-photon absorption ranges of these compounds.

Synthesis of π-Conjugated Soluble Poly(aryleneethynylene) Type Polymers and Their Properties

Abstract Pd-catalyzed coupling reactions with dihaloaromatic compounds X-Ar-X and diethynylaromatic compounds HC≡C-Ar′-C≡CH give new soluble π-conjugated polymers when Ar and/or Ar′ group is pyridine-2,5-diyl or has a long chain alkyl substituent.