Performance Comparisons of Polymer Semiconductors Synthesized by Direct (Hetero)Arylation Polymerization (DHAP) and Conventional Methods for Organic Thin Film Transistors and Organic Photovoltaics.

C-C bond forming reactions are central to the construction of π-conjugated polymers. Classical C-C bond forming reactions such as the Stille and Suzuki coupling reactions have been widely used in the past for this purpose. More recently, direct (hetero)arylation polymerization (DHAP) has earned a place in the spotlight with an increasing number of π-conjugated polymers being produced using this atom-economic and more sustainable chemistry. As semiconductors in organic electronics, the device performances of the polymers made by DHAP are of great interest and importance. This review compares the device performances of some representative π-conjugated polymers made using the DHAP method with those made using the conventional C-C bond forming reactions when they are used as semiconductors in organic thin film transistors (OTFTs) and organic photovoltaics (OPVs).

Synthesis and structure-property relationships of phthalimide and naphthalimide based organic π-conjugated small molecules.

Five organic π-conjugated small molecules with bithiophene-phthalimide backbones bearing alkyl chains of different symmetry, length and branching character were synthesized using optimized microwave and direct heteroarylation protocols. The chosen alkyl chains were 1-ethylpropyl, 1-methylbutyl, pentyl, hexyl and octyl. A sixth compound was also synthesized replacing the phthalimide terminal units with octylnaphthalimide for additional scope. Through the thorough analysis of both thermal and optical properties and the investigation of self-assembly tendencies by single crystal X-ray diffraction and variable angle spectroscopic ellipsometry it is evident that alkyl side chains and building block size influence many facets of material properties. Within this class of materials the 1-ethylpropyl derivative exhibited the most unique behaviour.

Preparation of a diphosphine with persistent phosphinyl radical character in solution: characterization, reactivity with O2, S8, Se, Te, and P4, and electronic structure calculations.

A new, easily synthesized diphosphine based on a heterocyclic 1,3,2-diazaphospholidine framework has been prepared. Due to the large, sterically encumbering Dipp groups (Dipp = 2,6-diisopropylphenyl) on the heterocyclic ring, the diphosphine undergoes homolytic cleavage of the P-P bond in solution to form two phosphinyl radicals. The diphosphine has been reacted with O(2), S(8), Se, Te, and P(4), giving products that involve insertion of elements between the P-P bond to yield the related phosphinic acid anhydride, sulfide/disulfide, selenide, telluride, and a butterfly-type perphospha-bicyclobutadiene structure with a trans,trans-geometry. All molecules have been characterized by multinuclear NMR spectroscopy, elemental analysis, and single-crystal X-ray crystallography. Variable-temperature EPR spectroscopy was utilized to study the nature of the phosphinyl radical in solution. Electronic structure calculations were performed on a number of systems from the parent diphosphine [H(2)P](2) to amino-substituted [(H(2)N)(2)P](2) and cyclic amino-substituted [(H(2)C)(2)(NH)(2)P](2); then, bulky substituents (Ph or Dipp) were attached to the cyclic amino systems. Calculations on the isolated diphosphine at the B3LYP/6-31+G* level show that the homolytic cleavage of the P-P bond to form two phosphinyl radicals is favored over the diphosphine by ~11 kJ/mol. Furthermore, there is a significant amount of relaxation energy stored in the ligands (52.3 kJ/mol), providing a major driving force behind the homolytic cleavage of the central P-P bond.

Anhydrous TEMPO-H: reactions of a good hydrogen atom donor with low-valent carbon centres.

In this paper, we report a novel synthesis of anhydrous 1-hydroxy-2,2,6,6-tetramethyl-piperidine (TEMPO-H). An X-ray crystal structure and full characterization of the compound are included. Compared to hydrated TEMPO-H, its anhydrous form exhibits improved stability and a differing chemical reactivity. The reactions of anhydrous TEMPO-H with a variety of low-valent carbon centres are described. For example, anhydrous TEMPO-H was reacted with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), an unsaturated NHC. Crystals of [CHNC(6)H(2)(CH(3))(3)](2)C···HO(NC(5)H(6)(CH(3))(4)), IMes···TEMPO-H, were isolated and a crystal structure determined. The experimental structure is compared to the results of theoretical calculations on the hydrogen-bonded dimer. Anhydrous TEMPO-H was also reacted with the saturated NHC, 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene (SIPr), giving the product [CH(2)Ni-Pr(2)C(6)H(3)](2)CH···O(NC(5)H(6)(CH(3))(4)). In contrast, the reaction of hydrated TEMPO-H with 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene gave small amounts of the hydrolysis product, N-(2,6-diisopropylphenyl)-N-[2-(2,6-diisopropylphenylamino)ethyl]formamide. Finally, anhydrous TEMPO-H was reacted with (triphenylphosphoranylidene)ketene to generate Ph(3)PC(H)C(=O)O(NC(5)H(6)(CH(3))(4)). A full characterization of the product, including an X-ray crystal structure, is described.

(η5-Cyclopentadienyl)(η6-phenoxathiin 10,10-dioxide)iron(II) hexafluoridophosphate and phenoxathiin 10,10-dioxide.

In the structure of the title complex salt, [Fe(C(5)H(5))(C(12)H(8)O(3)S)]PF(6), the coordinated cyclopentadienyl (Cp) and benzene ring planes are almost parallel, with a hinge angle between the planes of 0.8 (2)°. The hinge angle between the planes of the peripheral (coordinated and uncoordinated) benzene rings in the coordinated phenoxathiin 10,10-dioxide molecule is 169.9 (2)°, and the FeCp moiety is located inside the shallow fold of the heterocycle. The hinge angle between the benzene ring planes in the free heterocycle, C(12)H(8)O(3)S, is 171.49 (6)°.

[η6-1-Chloro-2-(pyrrolidin-1-yl)benzene](η5-cyclopentadienyl)iron(II) hexafluoridophosphate and (η5-cyclopentadienyl){2-[η6-2-(pyrrolidin-1-yl)phenyl]phenol}iron(II) hexafluoridophosphate.

In the complex salt [η(6)-1-chloro-2-(pyrrolidin-1-yl)benzene](η(5)-cyclopentadienyl)iron(II) hexafluoridophosphate, [Fe(C(5)H(5))(C(10)H(12)ClN)]PF(6), (I), the complexed cyclopentadienyl and benzene rings are almost parallel, with a dihedral angle between their planes of 2.3 (3)°. In a related complex salt, (η(5)-cyclopentadienyl){2-[η(6)-2-(pyrrolidin-1-yl)phenyl]phenol}iron(II) hexafluoridophosphate, [Fe(C(5)H(5))(C(16)H(17)NO)]PF(6), (II), the analogous angle is 5.4 (1)°. In both complexes, the aromatic C atom bound to the pyrrolidine N atom is located out of the plane defined by the remaining five ring C atoms. The dihedral angles between the plane of these five ring atoms and a plane defined by the N-bound aromatic C atom and two neighboring C atoms are 9.7 (8) and 5.6 (2)° for (I) and (II), respectively.

A new polymorph of 2,6-bis-(trifluoro-meth-yl)benzoic acid.

The asymmetric unit of a second polymorph of the title compound, C(9)H(4)F(6)O(2), contains five independent mol-ecules, which form hydrogen-bonded O-H⋯O dimers about inversion centers. The most significant structural difference between this structure and that of the first polymorph [Tobin & Masuda (2009 ▶). Acta Cryst. E65, o1217] is the hydrogen-bonded, dimeric orientation of the carb-oxy-lic acid functionalities.

1-(2,4,6-Triisopropyl-phen-yl)ethanone.

The title compound, C(17)H(26)O, is a di-ortho-alkyl substituted phenyl ethanone that exhibits a significant twisting of the ketone fragment relative to the aromatic ring [O-C-C-C torsion angle = 89.32 (17)°] due to steric pressure from the ortho-isopropyl groups. One ortho- and the para-isopropyl group exhibit orientational disorder with a refined site occupancy factor of 0.562 (3):0.438 (3).

(η-Cyclo-penta-dien-yl)[(1,2,3,4,4a,12a-η)-naphtho-[2,3-b][1,4]benzodioxine]iron(II) hexa-fluoridophosphate.

At 296 (2) K, both complexed rings in the iron(II) complex cation of the title salt, [Fe(C(5)H(5))(C(16)H(10)O(2))]PF(6), are almost parallel [dihedral angle between planes = 2.4 (3)°]. The quaternary C atoms of the complexed arene ring are located at the longest distance from the Fe atom, with Fe-C distances of 2.112 (4) and 2.105 (3) Å, which are slightly longer than the average Fe-C distance for this ring (2.083 Å). The Fe ion is located 1.660 (1) and 1.543 (1) Å, respectively, from the cyclo-penta-dienyl and the complexed arene ring.

1,3-Bis(2,6-diisopropyl-phen-yl)imidazolidinium tetra-phenyl-borate dichloro-methane disolvate.

The title compound, C(27)H(39)N(2) (+)·C(24)H(20)B(-)·2CH(2)Cl(2), is the first reported imidazolidinium cation with the sterically demanding 2,6-diisopropyl-phenyl groups in the 1,3-positions. The crystal structure is stabilized by weak inter-molecular C-H⋯π(arene) inter-actions. Due to the bulky nature of both the flanking 2,6-diisopropyl-phenyl substituents and the tetra-phenyl-borate counter-ion, anion inter-actions with the imidazolidinium H atom in the 2-position are not observed, also a first for this class of ortho-alkyl-substituted Arduengo-type carbene precursors.

1,3-Bis(2,6-diisopropyl-phen-yl)imidazolidin-2-yl-idene.

The title compound, C(27)H(38)N(2), is the first reported free imidazolidin-2-yl-idene carbene with 2,6-diisopropyl-phenyl groups in the 1,3-positions. The five-membered ring adopts a twisted conformation and the dihedral angle between the aromatic rings is 48.81 (6)°. Both isopropyl groups attached to one of the benzene rings are disordered over two sets of sites in 0.74 (2):0.26 (2) and 0.599 (8):0.401 (8) ratios.

Atomic Precision Graphene Model Compound for Bright Electrochemiluminescence and Organic Light-Emitting Diodes.

An N-annulated perylene diimide dimer, tPDI2N-hex, a graphene model compound with atomic precision, was investigated for luminescence applications. Electrochemiluminescence (ECL) of tPDI2N-hex was studied with tri-n-propylamine (TPrA) as a reducing coreactant. ECL-voltage curves along with spooling ECL spectra provided details of light generation mechanisms. The relative ECL quantum efficiency of the Ru(bpy)3(PF6)2/TPrA system was calculated to be 64%, which is superior to that of many other organic molecules because of the desired excited state in the absence of surface states. An organic light-emitting diode (OLED) fabricated with tPDI2N-hex displayed bright orange-red emission with a low color temperature, which is very desirable. It is plausible that the sterically constrained and thus orthogonal aromatic moieties in the tPDI2N-hex structure, with atomic precision graphene layer characteristics, lead to the excellent luminescence performances. The ECL and OLED studies of tPDI2N-hex showcase great application potentials of tPDI2N-hex in both solution-based ECL probes and solid-state light devices.

Facile synthesis of a semiconducting bithiophene-azine polymer and its application for organic thin film transistors and organic photovoltaics.

A new azine polymer poly(4,4'-didodecyl-2,2'-bithiophene-azine) (PDDBTA) was synthesized in only three steps. PDDBTA showed hole mobilities of up to 4.1 × 10-2 cm2 V-1 s-1 in organic thin film transistors (OTFTs) as a p-channel material. As a donor in organic photovoltaics (OPVs), power conversion efficiencies (PCEs) of up to 2.18% were achieved, which is the first example of using an azine-based polymer for OPVs. These preliminary results demonstrate the potential of bithiophene-azine polymers as a new type of low-cost semiconductor material for OPVs and other organic electronics.

Air and temperature sensitivity of n-type polymer materials to meet and exceed the standard of N2200.

N-type organic semiconductors are notoriously unstable in air, requiring the design of new materials that focuses on lowering their LUMO energy levels and enhancing their air stability in organic electronic devices such as organic thin-film transistors (OTFTs). Since the discovery of the notably air stable and high electron mobility polymer poly{[N,N'-bis (2-octyldodecyl)- naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,29-bisthiophene)} (N2200), it has become a popular n-type semiconductor, with numerous materials being designed to mimic its structure. Although N2200 itself is well-studied, many of these comparable materials have not been sufficiently characterized to compare their air stability to N2200. To further the development of air stable and high mobility n-type organic semiconductors, N2200 was studied in organic thin film transistors alongside three N2200-based analogues as well as a recently developed polymer based on a (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)benzo[1,2-b:4,5-b']difuran-2,6(3 H,7 H)-dione (IBDF) core. This IBDF polymer has demonstrated promising field-effect mobility and air stability in drop-cast OTFTs. While N2200 outperformed its analogues, the IBDF-based polymer displayed superior air and temperature stability compared to N2200. Overall, polymers with more heteroatoms displayed greater air stability. These findings will support the development of new air-stable materials, and further demonstrate the persistent need for the development of novel n-type semiconductors.

Synthesis of Poly(bisisoindigo) Using a Metal-Free Aldol Polymerization for Thin-Film Transistor Applications.

Typical syntheses of conjugated polymers rely heavily on organometallic reagents and metal-catalyzed cross-coupling reactions. Here, we show that an environmentally benign aldol polymerization can be used to synthesize poly(bisisoindigo), an analog of polyisoindigo with a ring-fused structural repeat unit. Owing to its extended conjugation length, poly(bisisoindigo) absorbs across the UV/vis/NIR spectrum, with an absorption tail that reaches 1000 nm. Due to the four electron-deficient lactam units on each repeat unit, poly(bisoindigo) possesses a low-lying LUMO, which lies at -3.94 eV relative to vacuum. Incorporation of the ring-fused monomer unit also lowered the overall torsional strain in the polymer backbone (relative to polyisoindigo), and the polymer was successfully used in prototype unipolar n-channel organic thin-film transistors.

(Eta5-cyclopentadienyl)[(1,2,3,4,4a,10a-eta)-1-methylthianthrene]iron(II) hexafluoridophosphate acetone 0.33-solvate.

The title complex salt, [Fe(C(5)H(5))(C(13)H(10)S(2))]PF(6).0.33C(3)H(6)O, obtained from an acetone-diethyl ether-dichloromethane mixture at 280 (2) K, has three cationic molecules (A-C), three hexafluoridophosphate counter-anions and one acetone solvent molecule in the asymmetric unit. Two of the three cations contain FeCp (Cp is cyclopentadienyl) inside the fold of the heterocycle. The dihedral angles between the planes of the external (complexed and uncomplexed) benzene rings in the thianthrene molecule are 146.5 (2) degrees for FeCp-out-of-fold molecule A, and 139.0 (3) and 142.5 (2) degrees for the two FeCp-in-fold molecules B and C, respectively. The complexed Cp and benzene rings in each molecule are almost parallel, with a dihedral angle between the planes of 0.2 (5) degrees for molecule A, 2.8 (5) degrees for B, and 2.19 (4) and 6.86 (6) degrees for the disordered Cp ring in C.

Hexaaqua-gallium(III) trinitrate trihydrate.

The title compound, [Ga(H(2)O)(6)](NO(3))(3)·3H(2)O, is isostructural to other known M(III) nitrate hydrates (M = Al, Cr, Fe). The structure contains two distinct octa-hedral Ga(OH(2))(6) units (each of symmetry) which are involved in inter-molecular hydrogen bonding with the three nitrate anions and three water mol-ecules within the asymmetric unit.

[2,2'-Bithiophene]-4,4'-dicarboxamide: a novel building block for semiconducting polymers.

A novel electron deficient building block [2,2'-bithiophene]-4,4'-dicarboxamide (BTDCA) was designed to lower the highest occupied molecular orbital (HOMO) energy level of polythiophenes in order to achieve a higher open circuit voltage (V oc) and thus a higher power conversion efficiency in polymer solar cells (PSCs). BTDCA dibromo monomers were conveniently synthesized in four steps, and were used to prepare three thiophene-based D-A polymers, P(BTDCA66-BT) (66BT), P(BTDCA44-BT) (44BT) and P(BTDCA44-TT) (44TT). All the polymers exhibited unipolar hole transport properties, exhibiting mobilities in the range of ∼10-4 to 10-2 cm2 V-1 s-1 with the highest hole mobility of up to 1.43 × 10-2 cm2 V-1 s-1 achieved for 44BT in bottom-gate bottom-contact organic thin film transistors (OTFTs). In PSCs, these polymers achieved high V oc's of 0.81-0.87 V when PCBM or ITIC was used as acceptor. When 44TT was used as donor and ITIC was used as acceptor, a power conversion efficiency (PCE) of up to 4.5% was obtained, a significant improvement when compared with the poly(3-hexylthiophene) (P3HT):ITIC devices, which showed the highest PCE of merely 0.92%.

Design and synthesis of stable indigo polymer semiconductors for organic field-effect transistors with high fluoride sensitivity and selectivity.

We report the design and synthesis of two novel indigo donor-acceptor (D-A) polymers, PIDG-T-C20 and PIDG-BT-C20, comprising an indigo moiety that has intramolecular hydrogen-bonds as the acceptor building block and thiophene (T) and bithiophene (BT) as the donor building block, respectively. PIDG-T-C20 and PIDG-BT-C20 exhibited characteristic p-type semiconductor performance, achieving hole mobilities of up to 0.016 and 0.028 cm2 V-1 s-1, respectively, which are highest values reported for indigo-based polymers. The better performing PIDG-BT-C20 was used for the fabrication of water-gated organic field-effect transistors (WGOFETs), which showed excellent stability at ambient conditions. The PIDG-BT-C20-based WGOFETs exhibited rapid response when fluoride ions were introduced to the water gate dielectric, achieving a limit of detection (LOD) of 0.40 mM. On the other hand, the devices showed much lower sensitivities towards other halide ions with the order of relative response: F- ≫ Cl- > Br- > I-. The high sensitivity and selectivity of PIDG-BT-C20 to fluoride over other halides is considered to be realized through the strong interaction of the hydrogen atoms of the N-H groups in the indigo unit with fluoride ions, which alters the intramolecular hydrogen-bonding arrangement, the electronic structures, and thus the charge transport properties of the polymer.

Poly(3-alkylthiophene)- block-poly(3-alkylselenophene)s: Conjugated Diblock Co-polymers with Atypical Self-Assembly Behavior.

Understanding self-assembly behavior and resulting morphologies in block co-polymer films is an essential aspect of chemistry and materials science. Although the self-assembly of amorphous coil-coil block co-polymers is relatively well understood, that of semicrystalline block co-polymers where each block has distinct crystallization properties remains unclear. Here, we report a detailed study to elucidate the rich self-assembly behavior of conjugated thiophene-selenophene (P3AT- b-P3AS) block co-polymers. Using a combination of microscopy and synchrotron-based X-ray techniques, we show that three different film morphologies, denoted as lamellae, co-crystallized fibers, and patchy fibers, arise from the self-assembly of these block co-polymers over a relatively narrow range of overall degrees of polymerization (30 < N < 90). Crystallization-driven phase separation occurs at a very low N (<35), and lamellar films are formed. Conversely, at medium N (50-60) and high N (>80), the thiophene and selenophene blocks co-crystallize into nanofibers, where medium N leads to much more mixing than high N. The overall tendency for phase separation in these systems follows rather different trends than phase separation in amorphous polymers in that we observe the greatest degree of phase separation at the lowest N. Finally, we demonstrate how each morphology influences transport properties in organic thin-film transistors comprised of these conjugated polymers.