Finely Tuned Fluorescence Emission of Polydiphenylacetylene Films Obtained by Copolymerization

PDPAs containing longer (octadecyl, C18) and shorter (methyl, C1) alkyl side chains in the same backbone are synthesized. The copolymerization of C1 and C18 monomers at a range of feed ratios afford high‐molecular‐weight (M _w > 10⁶) copolymers almost quantitatively. As the content of longer alkyl chain units in the copolymers increases, the emission band in the bulk film shifts to shorter wavelengths and the emission intensity increases. The lamellar layer distance increases with increasing C18 content. The excited species with shorter lifetimes decrease gradually with increasing C18 content, whereas the longer‐lasting emission increases. Fine tuning of the FL emission of PDPAs is achieved by simple copolymerization of monomers with different alkyl side‐chain lengths.     

Efficient Polymer Solar Cells Based on New Random Copolymers with Porphyrin‐Incorporated Side Chains

Two new wide bandgap block copolymers (PL1 and PL2) with porphyrin‐incorporated side chains are designed and used as electron donors for solution‐processed bulk heterojunction polymer solar cells. The photophysical, electrochemical, and photovoltaic properties, charge transport mobility and film morphology of these two block copolymers are investigated. Detailed investigations reveal that the different alkyl groups and electron‐withdrawing substituents on the porphyrin pendant units have significant influence on the polymer solubility, absorption energy level, band gap, and charge separation in the bulk‐heterojunction thin films, and thus the overall photovoltaic performances. Organic photovoltaic devices derived from these copolymers and ([6,6]‐phenyl‐C₇₁‐butyric acid methyl ester) (PC₇₁BM) acceptor show the best power conversion efficiencies of 5.83% and 7.14%, respectively. These results show that the inclusion of a certain proportion of side chain porphyrin group as a pendant in the traditional donor‐acceptor (D‐A) type polymer can broaden the molecular absorption range and become a full‐color absorbing molecule. The size of the porphyrin pendant also has an obvious effect on the properties of the molecule.     

Copolythiophenes with Hydrophilic and Hydrophobic Side Chains: Synthesis,Characterization, and Performance in Organic Field Effect Transistors

Statistical copolymers of regioregular polythiophene with hydrophobic hexyl side chains (P3HT) and hydrophilic 3,6‐dioxaheptyl side chains (P3DOHT) are synthesized by the GRIM method. A comparable study on the different polymers has been accomplished regarding solubility, thin film structure, and performance in organic field effect transistors (OFETs). DSC and XRD measurements are done to investigate the crystallinity of the copolymers. The novel functionalized fully π‐conjugated copolymers P(3HT‐co‐3DOHT) with feed molar ratios of 1:1, 2:1, and 1:2 show hole mobilities in the range of 10^?2 cm² V^?1 s^?1. Using poly(methyl methacrylate) as the dielectric layer in a top gate device architecture leads to air stable transistors without significant losses in the OFET performance over several months.     

Synthesis and Characterization of Poly(Dithieno[3,2‐b:2′,3′‐d]pyrrole) Derivatives Containing Thiophene Moieties and Their Application to Organic Devices

A series of conjugated polymers (PDTP, PDTPT, PDTPTT) based on dithieno[3,2‐b:2′,3′‐d]pyrrole (DTP) containing branched side‐chains is synthesized. The synthesized polymers show good solubility due to branched side‐chains in the organic solvent in the absence of heat treatment. To increase the oxidation potential, unsubstituted thiophene units are introduced into the polymer backbone. The introduction of unsubstituted thiophene units increases the oxidation potential, elevates degradation temperature, and enhances electronic properties. The PDTPTT FETs show the highest charge‐carrier mobility among the three polymers. These polymers are used as a donor material in bulk heterojunction solar cells, and the PDTPTT photovoltaic cells exhibit high performance.     

A New Class of Organosoluble Rigid‐Rod,Fully Aromatic Poly(1,3,4‐oxadiazole)s and Their Solid‐State Properties, 2. Solid‐State Properties

New symmetrical and unsymmetrical dialkoxy‐substituted aromatic poly(1,3,4‐oxadiazole)s are investigated by cyclovoltammetric measurements. The electrochemical redox behaviour of these materials is compared with the chemical structure. The reduction behaviour allows the estimation of the electron affinity, and shows that these polymers are suitable candidates for electron‐transport materials in electronic devices. Surprisingly it is found from UV‐vis and fluorescence spectroscopic measurements that the polyoxadiazole with linear alkoxy side chains (C16) shows a reversible thermochromism in solution as well as in the solid state. The changes in this temperature range are ascribed to a phase transition between aggregated chains, in solution as well as in the film, at room temperature and molecularly dissolved polymer chains at higher temperature. The other poly(1,3,4‐oxadiazole)s with branched alkoxy side chains exhibit an improved solubility and they are completely soluble in o‐dichlorobenzene at room temperature. The absorption and emission behaviour does not change in the temperature range from 25°C to 100°C. The fluorescence excitation studies of these poly(1,3,4‐oxadiazole)s show a blue emission in solution and in the film. Due to these results the poly(1,3,4‐oxadiazole)s are used as electron transport and blue emitting layers in electronic devices like diodes or polymer light emitting diodes (PLED).     

Crystalline and disordered state of poly(dihexylsilylene) copolymers

A systematic comparison of random copolymers, derived from poly(dihexylsilylene) (PDHS) by incorporation of monomeric units with shorter unbranched alkyl side chains, has been carried out based on calorimetry, variable temperature UV spectroscopy, and ²⁹Si MAS (magic angle spinning) solid state NMR investigations. Also, hexylmethylsilylene units and branched monomers have been copolymerized. Up to 10% comonomer with shorter linear side chains (i. e., pentyl to propyl) could be incorporated into PDHS without impeding the all-trans order of the crystalline phase. In this case, the UV absorption maximum of the crystalline low-temperature phase was affected only slightly according to the length and fraction of the comonomer side chains. A less ordered crystal structure (λ_max = 345–355 nm) was observed when the content of comonomers with shorter side chains was about 20%. Yet, all these materials form conformationally disordered mesophases. A clear disordering transition and corresponding thermochromism was not observed any more when 50% of propyl side chains were incorporated. The order of the crystalline and the mesophase is also strongly perturbed if only a small fraction (4%) of the side chains are branched at C².     

Oxidative Coupling Copolymerization of 4‐Methyltriphenylamine with Arenes

A novel synthetic method for the preparation of high‐molecular‐weight conjugated polymers is presented. It consists of the oxidation copolymerization of different arenes with triphenylamine. The structure of the copolymers was characterized by ¹H and ¹³C NMR spectra. The copolymers have good solubility in common organic solvents and are thermally stable. Photoluminescence (PL) spectra (see Figure) showed that the color of emission depends on the type of arene units in the copolymer chain. Cyclic voltammetry (CV) measurements revealed electrochemical activity of the copolymers.

PL spectra of the copolymers.     

Synthesis of N-Substituted Maleimides and Poly(styrene-co-N-maleimide) Copolymers and Their Potential Application as Photoresists

Poly(styrene-co-N-maleimide) copolymers bearing tert-butoxycarbonyl (t-BOC)-protected amine groups attached to side chains of varying lengths are synthesized via activators regenerated by electron transfer atom transfer radical polymerization (ARGET-ATRP) and investigated from the perspective of photoresist applications. The length of the alkyl substituents enables control of thermal properties as well as hydrophobicity, which are critically important for resist processing. Removal of the acid labile t-BOC group during deep-UV (DUV)exposure shifts solubility in the exposed areas and well-defined line space patterns of 1 µm are obtained for the selected copolymers. The correlation between glass transition temperature (T_g) and solubility contrast determines the lithographic performance where the copolymers with shorter alkyl chains exhibit promising results.     

Effect of Branched Side Chains on the Physicochemical and Photovoltaic Properties of Poly(3‐hexylthiophene) Isomers

Two P3HT isomers with branched alkyl side chains, P3EBT and P3MPT, are synthesized. The HOMO energy levels of P3EBT and P3MPT are ?5.35 and ?5.24 eV, respectively, which are significantly lower than that of P3HT with a linear side chain. The absorption edges of the two P3HT isomer films, especially those of P3EBT, are blue‐shifted in comparison with that of P3HT. A PSC based on P3EBT:IC₆₀BA (2:1 w/w) shows a high open‐circuit voltage of 0.98 V, which is the highest V_oc reported so far for polythiophene‐based PSCs. A PSC based on P3MPT:IC₇₀BA (2:1 w/w) exhibits a power conversion efficiency of 3.62% with a V_oc of 0.91 V. P3MPT is suitable for the application in tandem PSCs.     

Synthesis and Characterization of Isoindigo‐Based Polymers with Thermocleavable Side Chains

Stability of bulk heterojunction films for organic solar cells is a critical factor for commercial viability. One method to stabilize these films is to include cleavable side chains, which reduce the solubility of the polymers when removed. In order to study the stabilizing effect of cleavable side chains, a series of random copolymers using isoindigo with 0, 10, 20, 50, and 100% thermally cleavable side chains based on the tert‐butyloxycarbonyl (t‐BOC) group are synthesized. The polymers show a distinct one‐step thermal cleavage of the side chains, with no separable dealkylation and decarboxylation steps. The thermal stability in film is studied with transmission electron microscopy and atomic force microscopy. The polymer with all t‐BOC side chains on isoindigo significantly improves thermal stability with regard to crystal growth and phase separation in film. These results suggest BOC‐substitution can be used for large scale processing to produce insoluble polymer films with a high degree of thermal stability.     

Nano‐Scale Molecular Shapes of Water‐Soluble Chitin Derivatives Having Monodisperse Poly(2‐alkyl‐2‐oxazoline) Side Chains

The molecular shapes and the sizes of structures formed by chitin derivatives with monodisperse poly(2‐alkyl‐2‐oxazoline) side chains were investigated using atomic force microscopy (AFM), cryo‐transmission electron microscopy (cryo‐TEM), and small‐angle neutron scattering (SANS) analyses. A ring structure with an outside diameter of 45–60 nm and a cross‐sectional diameter of 10–18 nm was observed in the AFM image for chitin‐graft‐poly(2‐methyl‐2‐oxazoline) 1d (DP of the side chain, 8.5; [side chain]/[glucosamine unit], 0.53). From the cryo‐TEM observation of the graft copolymer 1d in 0.5 wt.‐% D₂O solution, an average diameter of 40 nm for the particles was determined, with a narrow size distribution. SANS measurements of the 0.5 wt.‐% D₂O solution of 1d revealed that the outside diameter of the particles and the cross‐sectional diameter were 57 nm and 8 nm, respectively. The absolute weight average molecular weight of 1d was determined to be 5.4 × 10⁵ by static light scattering. From these results it was concluded that 1d can form a unimolecular ring structure in aqueous solution. However, graft copolymers with fewer side chains ( 1c ; [side chain]/[glucosamine unit], 0.30) and with more side chains ( 1e ; [side chain]/[glucosamine unit], 0.96) did not form rings but instead formed monodisperse unimolecular spherical particles of diameters of 28–36 nm by AFM. A graft copolymer 1f with relatively long side chains (DP of side chain, 19.6; [side chain]/[glucosamine unit], 1.00) was also observed as a spherical particle by AFM (diameter: 30–40 nm by AFM; 40 nm by SANS). On the other hand, an intermolecular aggregate formation (diameter of the aggregate: 36–143 nm) was observed for graft copolymers 1a and 1b having short side chains (DP of side chains, 5.6; [side chain]/[glucosamine unit], 0.35 and 0.48, respectively), with a spherical molecular particle of diameter 36 nm by the AFM analysis. Chitin‐graft‐poly(2‐ethyl‐2‐oxazoline) ( 2 ) (DP of side chains, 21.7; [side chain]/[glucosamine unit], 0.95) generated larger aggregates of diameter 100–400 nm by AFM. The complexation behavior of graft copolymer 1d with magnesium 8‐anilino‐1‐naphthalenesulfonate (ANS) and with N‐phenyl‐1‐naphthylamine (PNA) was also examined by fluorescence measurement in an aqueous solution. It was found that graft copolymer 1d complexed with both ANS and PNA, and the binding constants were calculated to be 7.5 × 10⁴ M ^?1 and 5.3 × 10⁴ M ^?1, respectively.

Chemical structure of chitin‐graft‐poly(2‐alkyl‐2‐oxazoline).     

Conjugated Side Chain Tuning Effect of Indacenodithieno[3,2‐b]thiophene and Fluoro‐Benzothiadiazole‐Based Regioregular Copolymers for High‐Performance Organic Field‐Effect Transistors

Two regioregular indacenodithieno[3,2‐b ]thiophene and fluoro‐benzothiadiazole‐based donor–acceptor (D–A) type copolymers with different conjugated side chains of hexyl‐phenyl or hexyl‐thienyl are designed and synthesized to study the effects of the side chain on performance of organic field‐effect transistors (OFETs). The effect of the different conjugated side chains on the energy levels, optoelectronic properties, film morphology, and transistors performance as well as the solvent effect on the performance of both D–A copolymers are thoroughly studied. Top‐gate/bottom‐contact OFETs with a hexyl‐thienyl substituted polymer show higher hole mobility up to 0.211 cm² V⁻¹ s⁻¹ than 0.086 cm² V⁻¹ s⁻¹ observed for the polymer with hexyl‐phenyl side chains. In addition, the hexyl‐thienyl substituted side chain polymer shows relatively better stability under bias stress compared to hexyl‐phenyl conjugated side chain. This result sheds light on the impact of conjugated side chain engineering on the performance and stability of OFETs with D–A copolymers.     

Mixed Alkyl‐ and Alkoxy‐Substituted Poly[(phenylene ethynylene)‐alt‐(phenylene vinylene)] Hybrid Polymers: Synthesis and Photophysical Properties

Summary: We report the synthesis, characterisation and photophysical properties of mixed alkyl‐ and alkoxy‐substituted poly[(phenylene ethynylene)‐alt‐(phenylene vinylene)] hybrid polymers with the general constitutional unit: (? Ph? C?C? Ph? C?C? Ph? CH?CH? Ph? CH?CH? )_n ( 7 ). The polymers were obtained through the Horner‐Wadsworth‐Emmons olefination reaction of alkyl‐substituted luminophoric dialdehydes, 5a–b , and alkoxy‐substituted bisphosphonates. Contrary to their alkoxy‐substituted congeners, 10a–b , which exhibit solution fluorescence quantum yields close to unity, dialdehydes ( 5a–b ) fluoresce poorly at room temperature, but show phosphorescence at 77 K. High molecular weight polymers were obtained showing poor solubility compared to solely alkoxy‐substituted polymers ( 11 ) of the same backbone constitutional units. The presence of alkyl side groups in 7 leads to a 15 nm blue shift of their absorption spectra relative to 11 . Both types of polymers show however identical emission spectra with only a slight blue shift (3–4 nm) of the emission peak of 7 relative to 11 . This clearly proves that the chromophore system responsible for the emission in both types of compounds is located around the lower‐energy, alkoxy‐substituted phenylene‐vinylene portion of the polymers as confirmed by fluorescence kinetics investigations.

     

Synthesis and Characterization of Defined Branched Poly(propylene)s with Different Microstructures by Copolymerization of Propylene and Linear Ethylene Oligomers (Cn = 26–28) with Metallocenes/MAO Catalysts

Summary: Copolymers of propylene and hexacosene (C_n = 26–28) were synthesized in the presence of three different metallocene catalysts activated by methylaluminoxane. The poly(propylene) copolymers were prepared with iso‐, syndio‐, and atactic backbone microstructures by using different symmetric metallocenes such as rac‐{Me₂Si[2‐Me‐4‐(1‐Naph)Ind]₂}ZrCl₂ ( 1 ), [Ph₂C(Cp)(Flu)]ZrCl₂ ( 2 ), and [(H₃C)₂Si(9‐Flu)₂]ZrCl₂ ( 3 ) and up to 46.6 mol‐% comonomer content in the feed. The influence of the incorporated linear, ethylene‐based side chains into the poly(propylene) backbone were investigated by DSC, GPC, and ¹³C NMR. Generally, a decreasing content of comonomer in the feed enhances the activity of metallocene based catalysts. The determination of the branched microstructure by ¹³C NMR of the copolymers allows a smart identification of the amount of inserted hexacosene because of the separated backbone and side chain signals. Moreover, the relationship between the population of the side chains and the melting behavior of resulting copolymers were discussed. The melting point of the syndiotactic and isotactic poly(propylene) backbone decreases with increasing hexacosene content. When the inserted comonomer content exceeds 2 mol‐%, a second melting point of the crystallized ethylene based side chains can be observed which increases with an increasing amount of hexacosene.

Thermal behavior of isospecific hexacosene/propylene copolymers in dependence on the incorporation of hexacosene.     

Coplanar Donor–Acceptor Semiconducting Copolymers to Achieve Better Conjugated Structures: Side‐Chain Engineering

It is reported on the allocation effects of branched alkyl chains, when used as solubility and ordering enhancers of the conjugated donor–accepter (D –A ) copolymer backbones, on the ordering and π–π overlapping of the copolymers, that drastically affect the electrical properties of organic field‐effect transistors (OFETs). Triisopropylsilylethynyl‐benzo[1,2‐b :4,5‐b ′]dithiophene (TIPSBDT) and diketopyrrolopyrrole (DPP)‐based copolymers, which have two linear alkyl spacers (methylene (C 1) or butylene (C 4)) between the DPP and side‐substituent (C₁₀H₂₁)CH(C₈H₁₇) , are synthesized by Suzuki cross‐coupling. These copolymer films are spun cast onto a polymer‐treated SiO₂ dielectric surface, and some are further thermally annealed. The longer spacer, C 4, is found to efficiently enhance the coplanarity and conjugation of the D –A backbone, while the C 1 does not. The resulting C 4‐bridged TIPSBDT‐DPP‐based copolymer readily develops a superior π‐extended layer on the dielectric surface; the edge‐on chains with randomly oriented side chains can be closely packed with a short π‐planar distance (d ₍₀₁₀₎) of 3.57 Å. Its properties are superior to those of the short spacer C 1 system with d ₍₀₁₀₎ ≈3.93 Å. The C 4‐bridged TIPSBDT‐DPP copolymer films yield a field‐effect mobility up to 1.2 cm² V⁻¹ s⁻¹ in OFETs, 12 times as higher than that of the C 1 spacer system.

     

Preparation and Properties of Poly[(2‐alkylbenzimidazole)‐alt‐thiophene]s with Long Alkyl Side Chains

New alternative copolymers of thiophene and benzimidazole with alkyl side chains (alkyl = n‐C₅H₁₁, n‐C₇H₁₅, n‐C₁₀H₂₁ , n‐C₁₂H₂₅, and n‐C₁₈H₃₇) have been prepared. The polymerization by Stille coupling of 2‐alkyl‐4,7‐dibromobenzimidazoles with 2,5‐bis(trimethylstannyl)thiophene gave the corresponding copolymers in good yields. The new copolymers showed absorption and photoluminescence peaks at about 436–460 and 520–530 nm, respectively. Quantum yields of the photoluminescence were about 21–37% in DMF. Addition of NaOH led to a red‐shift of the absorption peak by about 60 nm. Their XRD patterns showed a diffraction peak in a low angle region (Bragg spacing d₁ = 17.4–35.4 Å) and a broad peak at about d₂ = 4.0 Å. Plots of the d₁ space vs. the number of carbon atom in the alkyl side chain gave a linear line with a slope of 1.35 Å per carbon, suggesting an end‐to‐end type packing of the copolymer in the solid.     

Synthesis and Properties of Soluble,Strongly Fluorescent Poly(m‐Phenylene)s with Pendant Stilbene‐Based Chromophores

The nickel‐catalyzed dehalogenative coupling of substituted m‐dichlorobenzenes afforded a new series of poly(m‐phenylene)s with pendant 2,6‐bisstilbenyl‐N‐alkylpyridinium tetrafluoroborate groups. Characterization of polymers was accomplished by viscosimetry, GPC, FT‐IR, NMR, X‐ray, differential scanning calorimetry, thermomechanical analysis, UV‐vis, and luminescence spectroscopy. The polymers were amorphous and showed an excellent solubility being readily soluble at room temperature in THF, chloroform, and chlorobenzene. Their T_g values ranged from 96 to 148°C. The polymers with pendant stilbene‐based chromophores were strongly fluorescent both in solution and in solid state. Their photoluminescence (PL) spectra showed maxima at 391–410 nm and 445–532 nm in solution and in thin film, respectively. The structure of the alkyl attached to the pyridinium nitrogen influenced remarkably the PL quantum yield of polymers. The most efficient fluorescent polymers obtained were those bearing long chain aliphatic group on this nitrogen. Their PL quantum yield in THF solution was up to 0.65.     

Electroluminescent and Photovoltaic Properties of the Crosslinkable Poly(phenylene vinylene) Derivative with Side Chains Containing Vinyl Groups

Summary: The photoluminescence (PL), electroluminescence (EL), and photovoltaic properties of a poly(phenylene vinylene) derivative with its side chains containing vinyl groups, poly[(2,5‐bis‐allyloxyphenylene vinylene)‐co‐(2‐methoxy‐5‐(2′‐ethylhexyloxy)phenylene vinylene)] (A‐PPV) are reported. A‐PPV with the active vinyl units in the end of its side chains can be crosslinked either by UV light irradiation or heating. The crosslinking does not change the color of light emitted from the A‐PPV polymer light‐emitting diode (PLED). FTIR confirms that the photo/heating‐induced crosslinking does not damage the conjugation of polymer at all. However, the PL and EL efficiency of A‐PPV decreased upon photoirradiation due to the existence of residual radicals in the solid‐state film. The relatively stable radicals function as a trap that quenches the luminescence. The blend of A‐PPV and noncrosslinkable polymer, poly(2‐methyloxy‐5‐ethylhexyloxyl‐1,4‐phenylene vinylene) (MEH‐PPV) was employed in the fabrication of PLEDs, and the PLED shows improved performance with a luminous efficiency of >1 cd · A⁻¹. The blend keeps the advantage of crosslinkability of the polymers and lessens the effects of the photo‐produced radicals. The photovoltaic cells comprised of A‐PPV and C₆₀ were fabricated and the energy conversion efficiency of the devices with and without UV treatment was similar, both around 0.3%. The UV irradiation on the blend film with C₆₀ seems resistant to the residual radicals.

The I‐V, L‐V plot of PLEDs with A‐PPV treated by UV light.     

Preparation of Polyisobutene‐graft‐Poly(methyl methacrylate) and Polyisobutene‐graft‐Polystyrene with Different Compositions and Side Chain Architectures through Atom Transfer Radical Polymerization (ATRP)

Polyisobutene‐graft‐poly(methyl methacrylate) and polyisobutene‐graft‐polystyrene with controlled compositions and side chain architectures were prepared through atom transfer radical polymerization (ATRP). Poly[isobutene‐co‐(p‐methylstyrene)‐co‐(p‐bromomethylstyrene)] (PIB) was used as a macroinitiator in the presence of CuCl or CuBr as a catalyst and dNbpy as a ligand. The compositions were controlled by the conversion of the monomer with polymerization time. The molecular weight distributions of the side chains were controlled through ATRP in the presence/absence of a halogen exchange reaction. DSC and DMA measurements showed that graft copolymers have two glass transition temperatures suggesting microphase separated behavior, which was also confirmed by SAXS measurements. The phase and dynamic mechanical behaviors were strongly affected by the compositions and/or the side chain architectures. The properties of the graft copolymers were controlled in a wide range leading to toughened glassy polymers or elastomers.     

Synthesis and Photovoltaic Properties of D–A Copolymers Based on 11,12‐Difluorodibenzo[a,c]phenazine Acceptor Unit

Four conjugated D‐π‐A copolymers, P1 – P4 , based on 11,12‐difluorodibenzo[a,c]phenazine as an acceptor unit, benzodithiophene (BDT) with an alkoxy side chain ( P1 and P2 ) or thiophene‐conjugated side chain ( P3 and P4 ) as a donor unit, and thiophene π‐bridges, are designed and synthesized to investigate the effect of the side‐chain nature and position on the photovoltaic performance of the conjugated polymer donor materials in polymer solar cells (PSCs). It is found that the copolymers of P3 and P4 with thiophene conjugated side chains on the BDT unit demonstrate broader absorption and better photovoltaic performance than that of P1 and P2 with alkoxy side chains on the BDT unit. The photovoltaic performance of P1 and P3 with an alkyl side chain on the thiophene π‐bridge close to the acceptor unit is improved over that of P2 and P4 with an alkyl side chain on the thiophene π‐bridge close to the donor unit, due to the lower steric hindrance of P1 and P3 . The results indicate that side‐chain engineering is very important for improving the photovoltaic performance of conjugated polymer donor materials.