Positioning lithium ions by host–guest chemistry combined with self‐assembly using a thiophene‐based all‐conjugated amphiphilic block copolymer

Self‐assembly of poly(3‐hexylthiophene) ( P3HT) driven by π–π stacking, combined with “Host‐Guest Chemistry” of ethylene glycol oligomer and lithium ion is demonstrated using a thiophene‐based all conjugated amphiphilic block copolymer, containing 93 mol % of P3HT and 7 mol % of poly(3‐(2‐(2‐{2‐[2‐(2‐methoxy‐ethoxy)‐ethoxy]‐ethoxy}‐ethyl))thiophene), P3EGT blocks. An ion chelating ability of ethylene glycol oligomers with lithium ions in the P3EGT block is confirmed using ¹H‐NMR spectrometry. This method could allow positioning lithium ions at the interface between P3HT domains and PC₆₁BM clusters, confirmed using XRD and photoluminescence quenching experiments. The compact lamellar P3HT domains by side repulsion driven self‐assembly of amphiphilic block copolymer and the molecular engineering of the interface with an optimized lithium contents are resulted in the improvement of photovoltaic performance in an organic solar cell (2.1–3.0%). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1068–1074     

One‐pot synthesis of conjugated poly(3‐hexylthiophene)‐b‐poly(phenyl isocyanide) hybrid rod–rod block copolymers and its self‐assembling properties

In this article, the synthesis of a series of conjugated rod–rod block copolymers based on poly(3‐hexylthiophene) (P3HT) and poly(phenyl isocyanide) (PPI) building blocks in a single pot is presented. Ni‐catalyzed Grignard metathesis polymerization of 2,5‐dibromo‐3‐hexylthiophene and subsequent addition of 4‐isocyanobenzoyl‐2‐aminoisobutyric acid decyl ester in the presence of Ni(dppp)Cl₂ as a single catalyst afford P3HT‐b‐PPI with tunable molecular weights and compositions. In solid state, microphase separation occurred as differential scanning calorimetric analysis of P3HT‐b‐PPI revealed two glass transition temperatures. In solutions, the copolymers can self‐assemble into spherical aggregates with P3HT core and PPI shell in tetrahydrofuran and exhibit amorphous state in CHCl₃. However, atomic force microscopy revealed that the block copolymers self‐assemble into nanofibrils on the substrate. These unique features warrant the resultant conjugated rod–rod copolymers' potential study in organic photovoltaic and other electronic devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2939–2947     

Morphology control of poly(3‐hexylthiophene)‐b‐poly(ethylene oxide) block copolymer by solvent blending

The use of mixed solvents provided an effective way to control the self‐assembly behavior and photophysical properties of a conjugated rod–coil block copolymer, poly(3‐hexylthiophene)‐b‐poly(ethylene oxide) (P3HT‐b‐PEO). It was shown that the balance between the π–π stacking of the P3HT and microphase separation of the copolymer could be dynamically controlled and shifted by solvent blending. Depending on the mixed solvent ratio (i.e., chloroform/methanol, anisole/chloroform, or anisole/methanol), the copolymer chains experienced different kinetic pathways, yielding a series of nanostructures such as disordered wormlike pattern, densely packed nanofibrils, and isolated nanofibrils. With the varying solvent selectivity, the P3HT‐b‐PEO chains displayed a hybrid photophysical property depending on the competition between intrachain and interchain excitonic coupling, resulting in the transformation between J‐ and H‐aggregation. Overall, this work offered an effective way to demonstrate the correlation and transformation between π–π stacking of P3HT and microphase separation, and how the conformation of P3HT chains influenced the photophysical properties of the copolymer during solvent blending. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 544–551     

Synthesis and characterization of six‐arm star polystyrene‐block‐poly (3‐hexylthiophene) copolymer by combination of atom transfer radical polymerization and click reaction

A novel six‐arm star block copolymer comprising polystyrene (PS) linked to the center and π‐conjugated poly (3‐hexylthiophene) (P3HT) was successfully synthesized using a combination of atom transfer radical polymerization (ATRP) and click reaction. First, star‐shaped PS with six arms was prepared via ATRP of styrene with the discotic six‐functional initiator, 2,3,6,7,10,11‐hexakis(2‐bromoisobutyryloxy)triphenylene. Next, the terminal bromides of the star‐shaped PS were substituted with azide groups. Afterward, the six‐arm star block copolymer PS‐b‐P3HT was prepared using the click coupling reaction of azide‐terminated star‐shaped PS with alkynyl‐terminated P3HT. Various techniques including ¹H NMR, Fourier‐transform infrared and size‐exclusion chromatography were applied to characterize the chemical structures of the intermediates and the target block copolymers. Their thermal behaviors and optical properties were investigated using differential scanning calorimetry and UV–vis spectroscopy. Moreover, atomic force microscopy (AFM) was utilized to observe the morphology of the star block copolymer films. In comparison with two linear diblock copolymer counterparts, AFM results reveal the effect of the star block copolymer architecture on the microphase separation‐induced morphology in thin films. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Trefoil‐Shaped Porous Nanographenes Bearing a Tribenzotriquinacene Core by Three‐fold Scholl Macrocyclization

Porous curved polycyclic aromatic compounds 6 and 14 bearing a tribenzotriquinacene (TBTQ) core encircled by an m,p,p,m,m,p,p,m,m,p,p,m‐cyclododecaphenylene belt were synthesized and characterized by NMR spectroscopy and mass spectrometry. These trefoil hydrocarbon macrocycles were constructed in high yield using an intramolecular three‐fold Scholl macrocyclization. X‐ray crystal analysis of 14 demonstrated a large wizard‐hat‐shaped structure with three pores (radii 2.9–3.0 Å). The π‐stacking aggregation of the hexa‐n‐dodecyloxy derivative 6 a and the chloride anion binding properties of 14 were studied by NMR spectroscopy. Such stacking and anion binding properties were much weaker in the singly 11 and doubly macrocyclized products 12 .     

Excited‐State Dynamic Planarization of Cyclic Oligothiophenes in the Vicinity of a Ring‐to‐Linear Excitonic Behavioral Turning Point

Excited‐state dynamic planarization processes play a crucial role in determining exciton size in cyclic systems, as reported for π‐conjugated linear oligomers. Herein, we report time‐resolved fluorescence spectra and molecular dynamics simulations of π‐conjugated cyclic oligothiophenes in which the number of subunits was chosen to show the size‐dependent dynamic planarization in the vicinity of a ring‐to‐linear behavioral turning point. Analyses on the evolution of the total fluorescence intensity and the ratio between 0–1 to 0–0 vibronic bands suggest that excitons formed in a cyclic oligothiophene composed of six subunits fully delocalize over the cyclic carbon backbone, whereas those formed in larger systems fail to achieve complete delocalization. With the aid of molecular dynamics simulations, it is shown that distorted structures unfavorable for efficient exciton delocalization are more easily populated as the size of the cyclic system increases.     

Solvent Vapor‐Induced Nanowire Formation in Poly(3‐hexylthiophene) Thin Films

Summary: Nanowire lengths and length‐to‐width aspect ratios in regioregular poly(3‐hexylthiophene) (P3HT) were simply controlled through changes in the solvent vapor pressure during solidification. It is demonstrated that the nanowires grew by rod‐to‐rod association, in which the molecular long axis of the P3HT chains appeared to be well‐oriented parallel to the silicon substrate (Si/SiO_x). The formation of the nanowires took place by one dimensional self‐assembly, governed by π‐π stacking of the P3HT units.

TEM high contrast images showing P3HT nanowires fabricated by spin‐coating under a solvent vapor pressure.     

Strong Solid‐state Luminescence Enhancement in Supramolecular Assemblies of Polyoxometalate and “Aggregation‐Induced Emission”‐active Phospholium

Two new supramolecular fluorescent hybrid materials, combining for the first time [M₆O₁₉]^2? (M=Mo, W) polyoxometalates (POMs) and aggregation‐induced emission (AIE)‐active 1‐methyl‐1,2,3,4,5‐pentaphenyl‐phospholium ( 1⁺ ), were successfully synthesized. This novel molecular self‐assembling strategy allows designing efficient solid‐state emitters, such as (1)₂[W₆O₁₉] , by directing favorably the balance between the AIE and aggregation‐caused quenching (ACQ) effects using both anion‐π⁺ and H‐bonding interactions in the solid state. Combined single‐crystal X‐ray diffraction, Raman, UV‐vis and photoluminescence analyses highlighted that the nucleophilic oxygen‐enriched POM surfaces strengthened the rigidity of the phospholium via strong C?H???O contacts, thereby exalting its solid‐state luminescence. Besides, the bulky POM anions prevented π–π stacking interactions between the luminophores, blocking detrimental self‐quenching effects.     

Aggregation of polythiophene homopolymer and block copolymer in solution utilizing the characteristics of pyridine at the side chain

Poly[3‐(5′‐hexylpyridine‐2′‐yl)thiophene] ( P3PT ) (M_n = 13900, H‐T content = 90%) was prepared by the regioselective Grignard metathesis reaction and the subsequent Kumada coupling polymerization. Likewise, poly(3‐hexylthiophene)‐b‐poly[3‐(5′‐hexylpyridine‐2′‐yl)thiophene] ( P3HT‐b‐P3PT ) (M_n = 17,300) was synthesized in the one‐pot and successive monomer addition protocol, in which the segment ratio was calculated to be 56 ( P3HT )/44 ( P3PT ) base on the ¹H NMR spectrum. The absorption and emission spectra of homopolymer P3PT(H) , obtained by the protonation of the pyridine nitrogen, in THF/cyclohexane shifted to the longer wavelength as compared with those collected in THF, suggesting the aggregation in poor solvent. The aggregation of P3PT induced by the addition of Sc(OTf)₃ could be controlled by the molar ratio of pyridine and scandium complex. The protonated block copolymer P3HT‐b‐P3PT(H) was also subjected to the aggregate formation. The absorption maximum in THF/CH₃OH showed a bathochromic shift and the fluorescence emission was almost quenched. From the ¹H NMR spectra and DLS measurements, P3HT‐b‐P3PT(H) forms nanometer scale aggregates particularly with the insolubility and stacking of non‐ionic P3HT in alcohol as the driving force. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3383–3389     

Controlled dispersion of polystyrene‐capped Au nanoparticles in P3HT:PC61BM and consequences upon active layer nanostructure

Numerous recent publications detail higher absorption and photovoltaic performance within organic photovoltaic (OPV) devices which are loaded with Au or Ag nanoparticles to leverage the light management properties of the localized surface plasmon resonance (LSPR). This report details the impact upon film morphology and polymer/nanoparticle interactions caused by incorporation of polystyrene‐coated Au nanoparticles (Au/PS) into the P3HT:PC₆₁BM bulk heterojunction film. Nanostructural analysis by transmission electron microscopy and X‐ray scattering reveals tunable Au/PS particle assembly that depends upon the choice of casting solvent, polymer chain length, film drying time, and Au/PS particle loading density. This Au/PS particle assembly has implications on the spectral position of the Au nanoparticle LSPR, which shifts from 535 nm for individually dispersed particles in toluene to 650 nm for particles arranged in large clusters within the P3HT:PC₆₁BM matrix. These results suggest a critical impact from PS/P3HT phase separation, which causes controlled assembly of a separate Au/PS phase in the nanoparticle/OPV composite; controlled Au/PS phase formation provides a blueprint for designing AuNP/OPV hybrid films that impart tunable optical behavior and potentially improve photovoltaic performance. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 709–720     

Synthesis of poly(3‐hexylthiophene)‐block‐poly(ethylene)‐block‐poly(3‐hexylthiophene) via a combination of ring‐opening olefin metathesis polymerization and grignard metathesis polymerization

Novel rod–coil–rod ABA triblock copolymers, poly(3‐hexylthiophene)‐block‐poly(ethylene)‐block‐poly(3‐hexylthiophene) (P3HT‐b‐PE‐b‐P3HT) were synthesized by using a combination of a Ru‐catalyzed ring‐opening metathesis polymerization of 1,4‐cyclooctadiene in the presence of a suitable chain transfer agent (CTA) and a Ni‐catalyzed Grignard metathesis polymerization of 5‐chloromagnesio‐2‐bromo‐3‐hexylthiophene followed by hydrogenation. Using this methodology, the molecular weights of the poly(butadiene) (PBD) or the P3HT blocks were controlled by adjusting the initial monomer/CTA or the initial monomer/macroinitiator ratio, respectively. In addition, the triblock structure was confirmed by selective oxidative degradation of the PBD block found in the intermediate P3HT‐b‐PBD‐b‐P3HT copolymer produced in the aforementioned method, followed by analysis of the degradation products. Thermal analysis and atomic force microscopy of P3HT‐b‐PE‐b‐P3HT revealed that the material underwent phase separation in the solid state, a feature which may prove useful for improving charge mobilities within electronic devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3810–3817     

Effects of aggregation of poly(3-hexylthiophene) in solution on uniaxial alignment of nanofibers during zone casting

We report on the effects of aggregation of P3HT with ordered conformation in solution on improving the uniaxial alignment of the P3HT nanofibers by zone casting.Two approaches were employed to change the aggregation of P3HT:P3HT blending with coil insulating polymer and ultrasonic oscillating.The insulator polymer(i.e.PS) which has good solubility in the solution would disturb the aggregation of P3HT to prevent the chains entanglement.The ultrasonic oscillation can further improve the P3HT aggregation with ordered conformation in the solution.As a result,the P3HT nanofibers in the film grew much orientedly by zone casting the ultrasonic oscillating P3HT/PS polymer blends solution than the same solvent P3HT solution without ultrasonic oscillating and blending.The P3HT tt-tt stacking direction is parallel to the alignment direction of the nanofibers.Meanwhile,the P3HT/PS blend ratio and PS molecular weight have influence on the uniaxial alignment of P3HT nanofibers.Only P3HT/PS is 1:1, the P3HT nanofibers oriented well.The low molecular weight PS can make the P3HT nanofibers orient better than that of the high molecular weight.     

A new methanol solvate and Hirshfeld analysis of π‐stacking in 2,3,6,7,10,11‐hexahydroxytriphenylene solvates

The structure of 2,3,6,7,10,11‐hexahydroxytriphenylene (hhtp) methanol monosolvate, C₁₈H₁₂O₆·CH₃OH, has triclinic symmetry (space group P). The compound has a three‐dimensional layered network structure formed by intermolecular hydrogen bonding. Structure analysis with Hirshfeld surfaces is shown to be a sensitive method for comparing π‐stacking effects in the five known solvates of hhtp. The title structure shows slightly weaker π‐stacking than the dihydrate, but stronger π‐stacking than the other three solvates.     

Exploring the relevance of thiophene rings as bridge unit in acceptor‐bridge‐donor dyes on self‐aggregation and performance in DSSCs

The possibility of dye charge recombination in DSSCs remains a challenge for the field. This consists of: (a) back‐transfer from the TiO₂ to the oxidized dye and (b) intermolecular electron transfer between dyes. The latter is attributed to dye aggregation due to dimeric conformations. This leads to poor electron injection which decreases the photocurrent conversion efficiency. Most organic sensitizers are characterized by an Acceptor‐Bridge‐Donor ( A ‐Bridge‐ D ) arrangement that is commonly employed to provide charge separation and, therefore, lowering the unwanted back‐transfer. Here, we address the intermolecular electron transfer by studying the dimerization and photovoltaic performance of a group of A ‐Bridge‐ D structured dyes. Specifically, eight famous sulfur containing π‐bridges were analyzed ( A and D remained fixed). Through quantum mechanical and molecular dynamics approaches, it was found that the formation of weakly stabilized dimers is allowed. The dyes with covalently bonded and fused thiophene rings as Bridges, 6d and 7d as well as 8d with a fluorene, would present high aggregation and, therefore, high probability of recombination processes. Conversely, using TiO₂ cluster and surface models, delineated the shortest bridges to improve the adsorption energy and the stability of the system. Finally, the elongation of the bridge up to 2 and 3 units and their photovoltaic parameters were studied. These results showed that all the sensitizers are able to provide similar photocurrent outcomes, regardless of whether the bridge is elongated. © 2017 Wiley Periodicals, Inc.     

Synthesis and self‐assembly of rod‐coil molecules with n‐shaped rod building block

The rod‐coil molecules with n‐shaped rod building block, consisting of an anthracene unit and two biphenyl groups linked together with acetylenyl bonds at the 1,8‐position of anthracene as a rigid rod segment, and the alkyl or alkyloxy chains with various length (i.e., methoxy‐ ( 1 ), octyl‐ ( 2 ), hexadecyl‐ ( 3 )) at the 10‐position of anthracene and poly(ethylene oxide) with the number of repeating units of 7 connected with biphenyl as coil segments were synthesized. The molecular structures were characterized by ¹H NMR and MALDI‐TOF mass spectroscopy. The self‐assembling behavior of new type of molecules 1–3 was investigated by means of DSC, POM, and SAXS at the bulk state. These molecules with a n‐shaped rod building block segment self‐assemble into supramolecular structures through the combination of π–π stacking of rigid rod building blocks and microphase separation of the rod and coil blocks. SAXS studies reveal that molecules 1 and 2 show hexagonal columnar and rectangular columnar structures in the liquid crystalline phase, respectively; meanwhile, molecules 1–3 self‐organize into lamellar structures in the crystalline state. In addition, self‐assembling studies of molecules 1–3 by DLS and TEM indicated that these molecules self‐assemble into elongated nanofibers in aqueous medium. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1415–1422, 2010     

Donor–acceptor rod–coil block copolymers comprising poly[2,7‐(9,9‐dihexylfluorene)‐alt‐bithiophene] and fullerene as compatibilizers for organic photovoltaic devices

The successful synthesis is described for a donor–acceptor rod–coil block copolymer comprising blocks of poly[2,7‐(9,9‐dihexylfluorene)‐alt‐bithiophene] (F6T2) and polystyrene functionalized with fullerene (PS(C₆₀)) (F6T2‐b‐PS(C₆₀)). This new material was obtained by combining Suzuki polycondensation with radical addition fragmentation chain transfer. The block copolymer was characterized by nuclear magnetic resonance, gel permeation chromatography, and optical spectroscopy methods. Photophysical data for (F6T2‐b‐PS(C₆₀)) and a related block copolymer (F6T2‐b‐PS(PCBM)) (PCBM, phenyl‐C61‐butyric acid methyl ester) are reported and their performance as compatibilizers in bulk heterojunction organic solar cells is assessed. It is demonstrated that the addition of the rod–coil block copolymers to the active layer extends the operational stability of organic photovoltaic devices. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 888–903     

Quantifying the efficiency of förster‐assisted optical gain in semiconducting polymer blends by excitation wavelength selective amplified spontaneous emission

We study the correlation between Förster resonance energy transfer (FRET) and optical gain properties in conjugated polymer blends based on regioregular poly(3‐hexylthiophene) (P3HT) and poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (F8BT). First, FRET dynamics are investigated with femtosecond transient absorption spectroscopy observing a sub‐picosecond energy transfer from F8BT to P3HT (550 fs) at medium doping levels (40% wt P3HT in F8BT). Amplified spontaneous emission (ASE) is then characterized in blends upon exciting predominantly the host and guest polymers, respectively. The corresponding density of absorbed photons at threshold conditions is compared upon host or guest photoexcitation as a method to quantitatively determine the FRET‐assisted ASE efficiencies. We observe a reduction in ASE efficiency upon host photoexcitation of 20%, in the best case, respect to guest photoexcitation. Our results confirm that even in strongly coupled host:guest mixtures delayed exciton population by energy transfer is subtle to losses ascribed to exciton–exciton annihilation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2311–2317.     

Oligo(p‐phenyleneethynylene)‐based coil–rod–coil triblock copolymer: Synthesis and controlled self‐organization in solution

The self‐assembling ability of block copolymers offers an attractive strategy for the organization of π‐conjugated polymers. This article reports the synthesis of a coil–rod–coil triblock copolymer consisting of oligo(p‐phenyleneethynylene) as the rodlike segment and polystyrene as the coil‐like segment. The chemical structure of the afforded triblock copolymer has been fully characterized by various spectroscopic techniques such as NMR, Raman, gel permeation chromatography, differential scanning calorimetry, ultraviolet–visible, and fluorescence spectroscopy. The small‐angle neutron scattering and photophysical measurements indicate that this triblock copolymer exhibits unique solvatochromatic behaviors through the interplay of aggregation‐induced π–π stacking and planarization of the conjugated backbone. Supramolecular gel nanostructures have been produced via the controlled assembly of the polymer into H‐aggregates. It has been demonstrated that the use of the solvent composition to influence chain conformations and thus to manipulate the packing of the conjugated polymer blocks is important for achieving control in the assembly of conducting polymers and associated optical characteristics. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6007–6019, 2005     

Influence of the bulkiness of the substituent on the aggregation and magnetic properties of poly(3‐alkylthiophene)s

A series of poly(3‐alkylthiophene)s (P3ATs) ( P1–P5 ) has been synthesized via a Ni(dppp)‐mediated polymerization, varying the bulkiness of the alkyl side chains in order to investigate the influence of the bulkiness of the alkyl substituent on the aggregation and magnetic properties of P3ATs. UV–Vis spectroscopy, performed in solution as well as in film, shows that the stacking of the polymers becomes more complicated as the bulkiness of the side chains increases. Both the π‐interactions and the planarization of the polymer chains are diminished. While aggregation is absent in poor solvent for the polymer with the most bulky side chains, aggregation was present in film, albeit slowed down. This behavior was also confirmed by X‐ray diffraction (XRD) and differential scanning calorimetry (DSC) experiments. Electron spin resonance (ESR) measurements, performed at 300 K on powders, confirmed the trend of decreasing supramolecular order with increasing bulkiness of the side‐chain. Magnetization measurements, performed at 5 and 300 K, are in line with our hypothesis on the influence of π‐interactions and the fraction of planar polymer chains on the coercivity and saturation magnetization, respectively. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 76–86     

Time‐Dependent Aggregation‐Induced Enhanced Emission,Absorption Spectral Broadening,and Aggregation Morphology of a Novel Perylene Derivative with a Large D–π–A Structure

Strong aggregation‐caused quenching of perylene diimides (PDI) is changed successfully by simple chemical modification with two quinoline moieties through C?C at the bay positions to obtain aggregation‐induced enhanced emission (AIEE) of a perylene derivative ( Cya‐PDI ) with a large π‐conjugation system. Cya‐PDI is weakly luminescent in the well‐dispersed CH₃CN or THF solutions and exhibits an evident time‐dependent AIEE and absorption spectra broadening in the aggregated state. In addition, morphological inspection demonstrates that the morphology of the aggregated form of Cya‐PDI molecules changed from plate‐shaped to rod‐like aggregates under the co‐effects of time and water. An edge‐to‐face arrangement of aggregation was proposed and discussed. The fact that the Cya‐PDI aggregates show a broad absorption covering the whole visible‐light range and strong intermolecular interaction through π–π stacking in the solid state makes them promising materials for optoelectric applications.