-phenylenevinylene)s L4. Fluorene-Based Conjugated Polymers L4.1. Fluorene-Based Copolymers ContainingElectron-Rich MoietiesM4.2. Fluorene-Based Copolymers ContainingElectron-Deﬁcient MoietiesN4.3. Fluorene-Based Copolymers ContainingPhosphorescent ComplexesQ5. Carbazole-Based Conjugated Polymers R5.1. Poly(2,7-carbazole)-Based Polymers R5.2. Indolo[3,2-

https://ir.nctu.edu.tw:443/bitstream/11536/6508/1/000271856900020.pdf

Synthesis of Conjugated Polymers for Organic Solar Cell Applications

When considering new sensory technologies one should look to nature for guidance. Indeed, living organisms have developed the ultimate chemical sensors. Many insects can detect chemical signals with perfect specificity and incredible sensitivity. Mammalian olfaction is based on an array of less discriminating sensors and a memorized response pattern to identify a unique odor. It is important to recognize that the extraordinary sensory performance of biological systems does not originate from a single element. In actuality, their performance is derived from a completely interactive system wherein the receptor is served by analyte delivery and removal mechanisms, selectivity is derived from receptors, and sensitivity is the result of analyte-triggered biochemical cascades. Clearly, optimal artificial sensory sys-

Conjugated polymer-based chemical sensors.

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Aryl-aryl bond formation one century after the discovery of the Ullmann reaction.

Since the discovery of highly conducting polyacetylene by Shirakawa, MacDiarmid, and Heeger in 1977, π-conjugated systems have attracted much attention as futuristic materials for the development and production of the next generation of electronics, that is, organic electronics. Conceptually, organic electronics are quite different from conventional inorganic solid state electronics because the structural versatility of organic semiconductors allows for the incorporation of functionality by molecular design. This versatility leads to a new era in the design of electronic devices. To date, the great number of π-conjugated semiconducting materials that have either been discovered or synthesized generate an exciting library of π-conjugated systems for use in organic electronics. 11 However, some key challenges for further advancement remain: the low mobility and stability of organic semiconductors, the lack of knowledge regarding structure property relationships for understanding the fundamental chemical aspects behind the structural design, and realization of desired properties. Organic field-effect transistors (OFETs) are a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals (drain, source, and gate electrodes). OFETs are not only essential building blocks for the next generation of cheap and flexible organic circuits, but they also provide an important insight into the charge transport of πconjugated systems. Therefore, they act as strong tools for the exploration of the structure property relationships of πconjugated systems, such as parameters of field-effect mobility (μ, the drift velocity of carriers under unit electric field), current on/off ratio (the ratio of the maximum on-state current to the minimum off-state current), and threshold voltage (the minimum gate voltage that is required to turn on the transistor). 17 Since the discovery of OFETs in the 1980s, they have attracted much attention. Research onOFETs includes the discovery, design, and synthesis of π-conjugated systems for OFETs, device optimization, development of applications in radio frequency identification (RFID) tags, flexible displays, electronic papers, sensors, and so forth. It is beyond the scope of this review to cover all aspects of π-conjugated systems; hence, our focus will be on the performance analysis of π-conjugated systems in OFETs. This should make it possible to extract information regarding the fundamental merit of semiconducting π-conjugated materials and capture what is needed for newmaterials and what is the synthesis orientation of newπ-conjugated systems. In fact, for a new science with many practical applications, the field of organic electronics is progressing extremely rapidly. For example, using “organic field effect transistor” or “organic field effect transistors” as the query keywords to search the Web of Science citation database, it is possible to show the distribution of papers over recent years as shown in Figure 1A. It is very clear

Semiconducting π-conjugated systems in field-effect transistors: a material odyssey of organic electronics.

About Supramolecular Assemblies of π-Conjugated Systems

± [1] S. Chandrasekhar, Liquid Crystals, Cambridge University Press, Cambridge 1992. [2] G. Blasse, G. J. Dirksen, A. Meijerink, J. F. Van der Pol, E. Neeleman, W. Drenth, Chem. Phys. Lett. 1989, 154, 420. [3] D. Markovitsi, I. Lecuyer, P. Lianos, J. Malthte, J. Chem. Soc., Faraday Trans. 1991, 87, 1785. [4] D. Markovitsi, F. Rigaut, M. Mouallem, J. Malthte, Chem. Phys. Lett. 1987, 135, 236. [5] D. Adam, F. Closs, T. Frey, D. Funhoff, D. Haarer, H. Ringsdorf, P. Schuhmacher, K. Siemensmeyer, Phys. Rev. Lett. 1993, 70, 457. [6] D. Adam, P. Schuhmacher, J. Simmerer, L. Hauuling, K. Siemensmeyer, K. H. Etzbach, H. Ringsdorf, D. Haarer, Nature 1994, 371, 141. [7] D. Adam, P. Schuhmacher, J. Simmerer, L. Hauuling, K. Paulus, K. Siemensmeyer, K. H. Etzbach, H. Ringsdorf, D. Haarer, Adv. Mater. 1995, 7, 276. [8] J. Simmerer, B. Glusen, W. Paulus, A. Kettner, P. Schuhmacher, A. Adam, K.-H. Etzbach, K. Siemensmeyer, J. H. Wendorff, H. Ringsdorf, D. Haarer, Adv. Mater. 1996, 8, 815. [9] T. Christ, B. Glusen, A. Greiner, A. Kettner, R. Sander, V. Stumpflen, V. Tsukruk, J. H. Wendorff, Adv. Mater. 1997, 9, 48. [10] T. Christ, V. Stumpflen, J. H. Wendorff, Macromol. Chem. Rapid Commun. 1997, 18, 93. [11] I. H. Stapff, V. Stumpflen, J. H. Wendorff, D. B. Spohn, D. Mobius, Liq. Cryst. 1997, 23, 613. [12] G. Lussem, J. H. Wendorff, Polym. Adv. Technol. 1998, 9, 443. [13] B. Glusen, W. Heitz, A. Kettner, J. H. Wendorff, Liq. Cryst. 1996, 20, 627. [14] B. Glusen, A. Kettner, J. Kopitzke, J. H. Wendorff, J. Non-Cryst. Solids 1998, 241, 113. [15] B. Glusen, Ordnung und Beweglichkeit: Untersuchungen zur Struktur und Dynamik diskotischer Flussigkristalle, Gorich & Weiershauser, Marburg, Germany 1997. [16] T. Christ, F. Geffarth, B. Glusen, A. Kettner, G. Lussem, O. Schafer, V. Stumpflen, J. H. Wendorff, V. V. Tsukruk, Thin Solid Films 1997, 302, 214. [17] C. Baehr, M. Ebert, G. Frick, J. H. Wendorff, Liq. Cryst. 1990, 7, 601. [18] G. Strobl, The Physics of Polymers, Springer, Berlin 1996, p. 157. [19] W. L. Winterbottom, Acta Metall. 1967, 15, 303. [20] H. Sato, S. Shinozaki, Surf. Sci. 1970, 22, 229. [21] B. Kevenhorster, Diploma Thesis, Universitat Marburg, Germany 1998. A Simple Method to Prepare Head-to-Tail Coupled, Regioregular Poly(3-alkylthiophenes) Using Grignard Metathesis**

A Simple Method to Prepare Head‐to‐Tail Coupled, Regioregular Poly(3‐alkylthiophenes) Using Grignard Metathesis

An investigation of the new synthetic method to synthesize regioregular, head-to-tail coupled poly(3-alkylthiophenes) using magnesium-halogen exchange (Grignard metathesis) called the GRIM method is described. Treatment of 2,5-dibromo-3-alkylthiophenes with a variety of alkyl and vinyl Grignard reagents resulted in two metalated, regiochemical isomers, namely, 2-bromo-3-alkyl-5-bromomagnesio- thiophene and 2-bromomagnesio-3-alkyl-5-bromothiophene in an 85:15 ratio. This ratio appears to be independent of reaction time, temperature, and Grignard reagent employed. Introduction of a catalytic amount of Ni(dppp)Cl2 to this isomeric mixture afforded poly(3-alkylthiophene) that contained greater than 95% HT-HT couplings (typically 98% HT couplings were seen). The high degree of regioregularity found in the polymer can be explained by a combination of kinetic and thermodynamic effects arising from steric and electronic effects found in the catalytic reaction. A series of reaction investigations led to a general explanation of the origin of regioregularity in polythiophene polymerization reactions. These reactions included kinetic studies and competition experiments.

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Regioregular, Head-to-Tail Coupled Poly(3-alkylthiophenes) Made Easy by the GRIM Method: Investigation of the Reaction and the Origin of Regioselectivity

Regioregular, head-to-tail coupled, poly(3-alkylthiophenes), synthesized by three different methods, were subjected to MALDI-TOF MS analysis. Polymer samples of both high and low polydispersities were examined. Polymer samples of narrow polydispersity were obtained by fractionation of the polymer by Soxhlet extraction with various solvents. Comparisons between the molecular weights calculated by MALDI and GPC of all fractionated polymer samples showed that GPC calculated molecular weights are a factor of 1.2−2.3 times higher than MALDI. The polydispersities calculated by MALDI were identical or slightly lower than those calculated by GPC. Polymer end-group compositions were also analyzed. We found that more than one type of end-group structure could be detected, and these structures are dependent on the synthetic method employed. Chemical modification of the end-group structure was also performed and monitored by MALDI with successful results. We observed that smaller polymer chains were subject to end-gr...

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Employing MALDI-MS on Poly(alkylthiophenes): Analysis of Molecular Weights, Molecular Weight Distributions, End-Group Structures, and End-Group Modifications

The development of polythiophene (PT) derivatives with essentially 100% head-to-tail (HT) couplings1,2 has led to the discovery of materials that self-assemble both in solution and in the solid state. Light-scattering studies on regioregular, HTpoly(3-dodecylthiophene) (HT-PDDT) show that a supramolecular organization occurs via intermolecular aggregation.3 This solution aggregation is precursive to a microcrystalline, self-assembled structure which has been characterized by X-ray studies.1,2,4 Polythiophenes possessing this metastable organization evidence high electrical conductivities1,2,5-8 and very small bandgaps. Previous work in our lab has shown that both conformational order and solid state organization in regioregular PT derivatives are remarkably sensitive to the placement and nature of the substituent chains.1,6,7,9 This sensitivity provides the opportunity to design new conducting polymers in which self-assembly is controlled by environmental factors. One remarkable example is HT-2,5-poly(thiophene-3-propionic acid) (3, PTPA). This polymer was designed such that upon deprotonation, water soluble polythiophene salts are formed.10 Both 3 and its partially deprotonated derivative 5 undergo protein-like hydrophobic assembly, with subsequent H-bond stabilization, to generate a self-assembled conducting polymer aggregate. Varying the size of the counterion in the carboxylate polymer changes the effective steric bulk of the substituent. Small cations favor a self-assembled (purple) state and large cations can completely disrupt the aggregated phase. In fact, a remarkable chemoselective counterion size-dependent chromaticity (Figure 1) is observed for polymer 5. The UV-vis λmax can be varied over a 130 nm range (from purple to yellow) simply by changing the countercation. Initially, we prepared the carboxylate precursor polymer 2 using the Ni(dppp)Cl2 cross-coupling method for the synthesis of HT polythiophenes.5,6,9 This method leads to low molecular weights (Mn ) 1.5-3.0 K), low yields (<5%), and polymers that show variable ionic chromaticity. However, the regioregular oxazoline polythiophene (2) (Mn ) 8 K, PDI ) 1.2) is prepared (Scheme 1) from monomer11 1 in high yields (84%)

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Self-Assembly and Disassembly of Regioregular, Water Soluble Polythiophenes: Chemoselective Ionchromatic Sensing in Water

A method of forming a regioregular polythiophene from a polymerization reaction is described. The method proceeds by combining a soluble thiophene having at least two leaving groups with an organomagnesium reagent to form a regiochemical isomer intermediate, and adding thereto an effective amount of Ni(II) catalyst to initiate the polymerization reaction.

Robert S. Loewe

Papers

A Simple Method to Prepare Head‐to‐Tail Coupled, Regioregular Poly(3‐alkylthiophenes) Using Grignard Metathesis

Regioregular, Head-to-Tail Coupled Poly(3-alkylthiophenes) Made Easy by the GRIM Method: Investigation of the Reaction and the Origin of Regioselectivity

Employing MALDI-MS on Poly(alkylthiophenes): Analysis of Molecular Weights, Molecular Weight Distributions, End-Group Structures, and End-Group Modifications

Self-Assembly and Disassembly of Regioregular, Water Soluble Polythiophenes: Chemoselective Ionchromatic Sensing in Water

A method of forming poly-(3-substituted) thiophenes