Effect of the side chain length on the optical and electrical properties of soluble PPV derivatives

2-Alkoxy-5-methoxy poly(1,4-phenylenevinylene) derivatives with different lengths of the alkoxy side chain have been synthesized via a modified Gilch polymerization. Their number-average molecular weights are in the range of 10,000–14,000. ¹H NMR, ¹³C NMR, FT-IR spectroscopies have shown that the polymer structures are the expected ones and were free from defects. The polymers are amorphous and show good thermal stability up to 300 °C. The optical absorption band of MB-PPV, MH-PPV, MO-PPV and MDD-PPV thin films are at 496 nm, 496 nm, 494 nm and 507 nm, respectively. Photoluminescence emission maxima of the above polymers appear at 624 nm, 582 nm, 629 nm and 578 nm, respectively. A composite photoluminescence response is observed at the exception of MO-PPV showing a single PL maximum. Light-emitting diodes (LEDs) based on these polymers were fabricated and characterized by current–voltage measurements. The comparison of the optical and electrical properties of these different polymers showed a small influence of the length of the side alkoxy chain and/or to the length of the main polymeric chain.     

Alkyl-π engineering in state control toward versatile optoelectronic soft materials

Abstract

Organic π-conjugated molecules with extremely rich and tailorable electronic and optical properties are frequently utilized for the fabrication of optoelectronic devices. To achieve high solubility for facile solution processing and desirable softness for flexible device fabrication, the rigid π units were in most cases attached by alkyl chains through chemical modification. Considerable numbers of alkylated-π molecular systems with versatile applications have been reported. However, a profound understanding of the molecular state control through proper alkyl chain substitution is still highly demanded because effective applications of these molecules are closely related to their physical states. To explore the underlying rule, we review a large number of alkylated-π molecules with emphasis on the interplay of van der Waals interactions (vdW) of the alkyl chains and π–π interactions of the π moieties. Based on our comprehensive investigations of the two interactions’ impacts on the physical states of the molecules, a clear guidance for state control by alkyl-π engineering is proposed. Specifically, either with proper alkyl chain substitution or favorable additives, the vdW and π–π interactions can be adjusted, resulting in modulation of the physical states and optoelectronic properties of the molecules. We believe the strategy summarized here will significantly benefit the alkyl-π chemistry toward wide-spread applications in optoelectronic devices.     

A Chemically Doped Naphthalenediimide‐Bithiazole Polymer for n‐Type Organic Thermoelectrics

The synthesis of a novel naphthalenediimide (NDI)‐bithiazole (Tz2)‐based polymer [P(NDI2OD‐Tz2)] is reported, and structural, thin‐film morphological, as well as charge transport and thermoelectric properties are compared to the parent and widely investigated NDI‐bithiophene (T2) polymer [P(NDI2OD‐T2)]. Since the steric repulsions in Tz2 are far lower than in T2, P(NDI2OD‐Tz2) exhibits a more planar and rigid backbone, enhancing π–π chain stacking and intermolecular interactions. In addition, the electron‐deficient nature of Tz2 enhances the polymer electron affinity, thus reducing the polymer donor–acceptor character. When n‐doped with amines, P(NDI2OD‐Tz2) achieves electrical conductivity (≈0.1 S cm^?1) and a power factor (1.5 µW m^?1 K^?2) far greater than those of P(NDI2OD‐T2) (0.003 S cm^?1 and 0.012 µW m^?1 K^?2, respectively). These results demonstrate that planarized NDI‐based polymers with reduced donor–acceptor character can achieve substantial electrical conductivity and thermoelectric response.     

Pd- and Ni-catalyzed cross-coupling reactions in the synthesis of organic electronic materials

Organic molecules and polymers with extended π-conjugation are appealing as advanced electronic materials, and have already found practical applications in thin-film transistors, light emitting diodes, and chemical sensors. Transition metal (TM)-catalyzed cross-coupling methodologies have evolved over the past four decades into one of the most powerful and versatile methods for C–C bond formation, enabling the construction of a diverse and sophisticated range of π-conjugated oligomers and polymers. In this review, we focus our discussion on recent synthetic developments of several important classes of π-conjugated systems using TM-catalyzed cross-coupling reactions, with a perspective on their utility for organic electronic materials.     

Enhancing Molecular n‐Type Doping of Donor–Acceptor Copolymers by Tailoring Side Chains

In this contribution, for the first time, the molecular n‐doping of a donor–acceptor (D–A) copolymer achieving 200‐fold enhancement of electrical conductivity by rationally tailoring the side chains without changing its D–A backbone is successfully improved. Instead of the traditional alkyl side chains for poly{[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl](NDI)‐alt‐5,5′‐(2,2′‐bithiophene)} (N2200), polar triethylene glycol type side chains is utilized and a high electrical conductivity of 0.17 S cm^?1 after doping with (4‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazol‐2‐yl)phenyl)dimethylamine is achieved, which is the highest reported value for n‐type D–A copolymers. Coarse‐grained molecular dynamics simulations indicate that the polar side chains can significantly reduce the clustering of dopant molecules and favor the dispersion of the dopant in the host matrix as compared to the traditional alkyl side chains. Accordingly, intimate contact between the host and dopant molecules in the NDI‐based copolymer with polar side chains facilitates molecular doping with increased doping efficiency and electrical conductivity. For the first time, a heterogeneous thermoelectric transport model for such a material is proposed, that is the percolation of charge carriers from conducting ordered regions through poorly conductive disordered regions, which provides pointers for further increase in the themoelectric properties of n‐type D–A copolymers.     

Synthesis,characterization and structure dependence of thermochromism of polythiophene derivatives

In order to investigate the effect of the bulky pendant group and the spacer length between the pendant group and polythiophene main chain on the optical property of polythiophene backbone, a series of polythiophene derivatives were synthesized via copolymerization of 3-hexylthiophene with four different types of 4-((4-(phenyl)azo)phenoxy)alkyl-3thienylacetate. The alkyl spacers with different lengths, i.e., butyl, hexyl, octyl and undecyl groups were used between the bulky azobenzene group and the thiophene ring. The compositions and structures of these polythiophene derivatives were characterized. The structural dependence of thermochromic behaviour of these copolymers were systematically studied and results compared with poly(3-hexylthiophene) (P3HeT). A thermochromic temperature coefficient (C_TC) was defined for the first time in an attempt to quantitatively compare the sensitivity of the thermochromism in the copolymers. The results have shown that these copolymers with a bulky azobenzene group in side chain have a higher (C_TC) value than P3HT and the C_TC value of the copolymers increase with increasing the spacer length.     

Inhibition of Alzheimer amyloid β aggregation by polyvalent trehalose

Abstract

A glycopolymer carrying trehalose was found to suppress the formation of amyloid fibrils from the amyloid β peptide (1–42) (Aβ), as evaluated by thioflavin T assay and atomic force microscopy. Glycopolymers carrying sugar alcohols also changed the aggregation properties of Aβ, and the inhibitory effect depended on the type of sugar and alkyl side chain. Neutralization activity was confirmed by in vitro assay using HeLa cells. The glycopolymer carrying trehalose strongly inhibited amyloid formation and neutralized cytotoxicity.     

Study and explanation about the morphological,electrochemical and structural properties of differently synthesized polypyrrole

Polypyrrole (ppy), a conducting polymer was synthesized by four different polymerization methods viz. electrochemical polymerization (EP), interfacial polymerization (IP), chemical oxidative polymerization (COP) and template-assisted polymerization (TAP). The change in morphology that occurred due to the variation of polymerization method used was studied with scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The samples were analyzed by Fourier transform infrared (FT-IR) spectroscopy to confirm the successful polymerization of pyrrole to polypyrrole with the appearance of characteristic bands for N–H stretching, C–N stretching, ppy ring stretching, C–H and C–C bending vibrations. Optical studies were done by UV–Vis absorption spectroscopy that displayed π→π^* and polaronic/bipolaronic transitions of ppy. XRD analysis revealed amorphous nature of ppy. Examination of SEM micrographs disclosed that ppy synthesized by EP had the typical cauliflower structure while ppy formed by IP were in the form of chain like network with a thickness of 250–290 nm, COP resulted in the formation of interlinked microspheres of polypyrrole and TAP formed polypyrrole nanofibers. Electrochemical characterization showed that ppy prepared by EP had the lowest redox activity and the samples were also tested to detect Pb²⁺.     

Energy Storage Application of Conducting Polymers Featuring Dual Acceptors: Exploring Conjugation and Flexible Chain Length Effects

Solution-processable conducting polymers (CPs) are a compelling alternative to inorganic counterparts because of their potential for tuning chemical properties and creating flexible organic electronics. CPs, which typically comprise either only an electron donor (D) or its alternative combinations with an electron acceptor (A), exhibit charge transfer behavior between the units, resulting in an electrical conductivity suitable for utilization in electronic devices and for energy storage applications. However, the energy storage behavior of CPs with a sequence of electron acceptors (A–A), has rarely been investigated, despite their promising lower band gap and higher charge carrier mobility. Utilizing the aforesaid concept herein, four CPs featuring benzodithiophenedione (BDD), and diketopyrrolepyrrole (DPP) are synthesized. Among them, the BDDTH-DPPEH polymer exhibited the highest specific capacitance of 126.5 F g⁻¹ at a current density of 0.5 A g⁻¹ in an organic electrolyte over a wide potential window of −0.6–1.4 V. Notably, the supercapacitor properties of the polymeric electrode materials improved with increasing conjugation length by adding thiophene donor units and shortening the alkyl chain lengths. Furthermore, a symmetric supercapacitor device fabricated using BDDTH-DPPEH exhibited a high-power density of 4000 W kg⁻¹ and an energy density of 31.66 Wh kg⁻¹.     

Orientation phenomena in chromophore DR1-containing polymer films and their non-linear optical response

The effectiveness of chromophore alignment in polymer films following corona poling can be assessed by the generated second harmonic signal. Optimization of the stability and strength of this nonlinear optical response may improve with a better understanding of the underlying principal order phenomena. Structural analysis by vibrational, optical, and ¹H NMR spectroscopy reveals side chain tacticity, aggregation effects, and changes in orientation as a function of temperature. Co-polymers with the functionalized chromophore Disperse Red 1 methacrylate (MDR1) were prepared for three different methacrylate types. High side chain polarity and short side chain length increase generally chromophore aggregation in films, whereas the very long poly-ether side chains in PMEO based co-polymers are wrapped separately around the DR1 entities. Side chain tacticity depends on space requirements, but also on the capacity of side groups to form OH-bridges. Side chain tacticity might present an additional parameter for the assessment of chromophore aggregation and poling induced alignments. Stepwise heating of co-polymer films causes an increase in the number of random over ordered side chain arrangements. Cross-linking by anhydride formation is observed after heating the methacrylic acid based co-polymer.     

Pyridinic Nitrogen Doped Carbon Dots Supply Electrons to Improve Photosynthesis and Extracellular Electron Transfer of Chlorella pyrenoidosa

Optimizing photosynthesis is imperative for providing energy and organics for all life on the earth. Here, carbon dots doped with pyridinic nitrogen (named lev-CDs) are synthesized by the one-pot hydrothermal method, and the structure–function relationship between functional groups on lev-CDs and photosynthesis of Chlorella pyrenoidosa (C. pyrenoidosa) is proposed. Pyridinic nitrogen plays a key role in the positive effect on photosynthesis caused by lev-CDs. In detail, lev-CDs act as electron donors to supply photo-induced electrons to P680⁺ and QA⁺, causing electron transfer from lev-CDs to the photosynthetic electron transport chain in the photosystems. In return, the recombination efficiency of electron–hole pairs on lev-CDs decreases. As a result, the electron transfer rate in the electron transport chain, the activity of photosystem II, and the Calvin cycle are enhanced. Moreover, the electron transfer rate between C. pyrenoidosa and external circumstances enhanced by lev-CDs is about 50%, and electrons exported from C. pyrenoidosa can be used to reduce iron(III). This study is of great significance for engineering nanomaterials to improve photosynthesis.     

Enhancing Performance of Nonfullerene Acceptors via Side‐Chain Conjugation Strategy

A side‐chain conjugation strategy in the design of nonfullerene electron acceptors is proposed, with the design and synthesis of a side‐chain‐conjugated acceptor (ITIC2) based on a 4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b :4,5‐b′ ]di(cyclopenta‐dithiophene) electron‐donating core and 1,1‐dicyanomethylene‐3‐indanone electron‐withdrawing end groups. ITIC2 with the conjugated side chains exhibits an absorption peak at 714 nm, which redshifts 12 nm relative to ITIC1. The absorption extinction coefficient of ITIC2 is 2.7 × 10⁵m ^?1 cm^?1, higher than that of ITIC1 (1.5 × 10⁵m ^?1 cm^?1). ITIC2 exhibits slightly higher highest occupied molecular orbital (HOMO) (?5.43 eV) and lowest unoccupied molecular orbital (LUMO) (?3.80 eV) energy levels relative to ITIC1 (HOMO: ?5.48 eV; LUMO: ?3.84 eV), and higher electron mobility (1.3 × 10^?3 cm² V^?1 s^?1) than that of ITIC1 (9.6 × 10^?4 cm² V^?1 s^?1). The power conversion efficiency of ITIC2‐based organic solar cells is 11.0%, much higher than that of ITIC1‐based control devices (8.54%). Our results demonstrate that side‐chain conjugation can tune energy levels, enhance absorption, and electron mobility, and finally enhance photovoltaic performance of nonfullerene acceptors.     

Comparative study of porphyrin derivatives in monolayers at the air-water interface and in Langmuir-Blodgett films

The orientation and aggregation of various porphyrin derivatives at the air-water interface and in Langmuir-Blodgett films were investigated. Monolayer properties of these molecules, where long alkyl chain(s) were covalently bound through different functionality of varying hydrophilicity were studied by measuring surface pressure area isotherms. Such derivatives, where ether functionality (functionalities) was (were) used for linking long alkyl chain(s), did not form uniform monolayer; instead they were found to form multilayer clusters or aggregates on the water surface. On the other hand, porphyrin derivative functionalized at the four peripheral phenyl rings with eight hexadecyl ether chains formed stable spherical vesicles when deposited on mica. Tetra N-alkyl pyridinium porphyrins with long alkyl chain were found to form various phases on the water surface. Evidence of transition from horizontal orientation to vertical orientation of porphyrin rings of porphyrin molecules having C₁₄ chains was observed. This type of transition was lost with the porphyrin molecule with a relatively smaller chain (C₈).     

Programmed self-assembly of large π-conjugated molecules into electroactive one-dimensional nanostructures

Abstract

Electroactive one-dimensional (1D) nano-objects possess inherent unidirectional charge and energy transport capabilities along with anisotropic absorption and emission of light, which are of great advantage for the development of nanometer-scale electronics and optoelectronics. In particular, molecular nanowires formed by self-assembly of π-conjugated molecules attract increasing attention for application in supramolecular electronics. This review introduces recent topics related to electroactive molecular nanowires. The nanowires are classified into four categories with respect to the electronic states of the constituent molecules: electron donors, acceptors, donor–acceptor pairs and miscellaneous molecules that display interesting electronic properties. Although many challenges still remain for practical use, state-of-the-art 1D supramolecular nanomaterials have already brought significant advances to both fundamental chemical sciences and technological applications.     

9,9′-联芴烯衍生物在有机光伏电池中的应用

由于具有独特的14π电子芳香结构和扭曲的非平面构型,9,9′-联芴烯衍生物成为近年来被广泛研究的一类新型有机光伏材料。9,9′-联芴烯衍生物含有两个刚性平面内的联苯单元,因此具有良好的热稳定性和化学稳定性;且其具有优良的光电特性,很容易接受电子,从而提升自身的最低未占分子轨道(LUMO)能级,使得其有机光伏器件的开路电压增大。此外,9,9′-联芴烯有12个不同的取代位,与富勒烯衍生物相比,其结构更具灵活性。但是,该类化合物的电子迁移率较低,使得其光伏电池的光电转化效率过低。如何通过提高该类材料的电子迁移率、拓展其光谱吸收范围和吸收强度来提高光伏器件的光电转换效率,受到越来越多的关注和研究。阐述了近年来联芴烯衍生物在有机光伏电池中的研究进展,并对其结构、性能进行了简要的分析。最后,对联芴烯类材料的发展前景进行了展望。     

Side Chain Engineering on Medium Bandgap Copolymers to Suppress Triplet Formation for High‐Efficiency Polymer Solar Cells

Suppression of carrier recombination is critically important in realizing high‐efficiency polymer solar cells. Herein, it is demonstrated difluoro‐substitution of thiophene conjugated side chain on donor polymer can suppress triplet formation for reducing carrier recombination. A new medium bandgap 2D‐conjugated D–A copolymer J91 is designed and synthesized with bi(alkyl‐difluorothienyl)‐benzodithiophene as donor unit and fluorobenzotriazole as acceptor unit, for taking the advantages of the synergistic fluorination on the backbone and thiophene side chain. J91 demonstrates enhanced absorption, low‐lying highest occupied molecular orbital energy level, and higher hole mobility, in comparison with its control polymer J52 without fluorination on the thiophene side chains. The transient absorption spectra indicate that J91 can suppress the triplet formation in its blend film with n‐type organic semiconductor acceptor m ‐ITIC (3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone)‐5,5,11,11‐tetrakis(3‐hexylphenyl)‐dithieno[2,3‐d:2,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]‐dithiophene). With these favorable properties, a higher power conversion efficiency of 11.63% with high V _OC of 0.984 V and high J _SC of 18.03 mA cm^?2 is obtained for the polymer solar cells based on J91 /m ‐ITIC with thermal annealing. The improved photovoltaic performance by thermal annealing is explained from the morphology change upon thermal annealing as revealed by photoinduced force microscopy. The results indicate that side chain engineering can provide a new solution to suppress carrier recombination toward high efficiency, thus deserves further attention.     

25th Anniversary Article: High‐Mobility Hole and Electron Transport Conjugated Polymers: How Structure Defines Function

The structural organization of three different families of semicrystalline π‐conjugated polymers is reported (poly(3‐hexylthiophene) (P3HT), poly[2,6‐(4,4‐bis‐alkyl‐4H‐cyclopenta‐[2,1‐b;3,4‐b0]‐dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)](cyclopentadithiophene‐benzothiadiazole) (CDT‐BTZ) and poly(N,N"‐bis‐2‐octyldodecylnaphtalene‐1,4,5,8‐bis‐dicarboximide‐2,6‐diyl‐alt‐5,5–2,2‐bithiophene (P(NDI2OD‐T2))). These have triggered significant interest for their remarkable charge‐transport properties. By performing molecular mechanics/dynamics simulations with carefully re‐parameterized force fields, it is illustrated in particular how the supramolecular organization of these conjugated polymers is driven by an interplay between the length and nature of the conjugated monomer unit and the packing of their alkyl side chains, and to what extent it impacts the charge‐carrier mobility, as monitored by quantum‐chemical calculations of the intermolecular hopping transfer integrals. This Progress Report is concluded by providing generic guidelines for the design of materials with enhanced degrees of supramolecular organization.     

Helically assembled π-conjugated polymers with circularly polarized luminescence

We review the recent progress in the field of helically assembled π-conjugated polymers, focusing on aromatic conjugated polymers with interchain helical π-stacking that exhibit circularly polarized luminescence (CPL). In Part 1, we discuss optically active polymers with white-colored CPL and the amplification of the circular polarization through liquid crystallinity. In Part 2, we focus on the stimuli-responsive CPL that results from changes in the conformation and aggregation state of π-conjugated molecules and polymers. In Part 3, we discuss the self-assembly of achiral cationic π-conjugated polymers into circularly polarized luminescent supramolecular nanostructures with the aid of other chiral molecules.     

The Phonon Modes with Strong Electron–Phonon Interactions in p- and n-Type High T c Superconductors

The phonon modes with strong electron–phonon interactions were investigated by two-phonon Raman scattering in p- and n-type high T _c superconductors. In p-type superconductors, the strong electron–phonon interaction mode changes from the breathing mode at (π, π) to the half breathing mode at (π, 0) as carrier density increases across the optimum doping in LSCO or the 60 K phase in YBCO. It is in good accordance with the change of the superconducting coherent peak position in k-space. In n-type superconductors, the strong electron–phonon interaction modes change from (0.4π, 0.4π) to (0.4π, 0) at the insulator–superconductor transition. Electron–phonon interactions play an important role in superconductivity.     

Physicochemical characteristics and in vitro release from oil-based vehicles of peptidomimetics: parenteral depots for intra-articular administration

Results: Basic physicochemical properties including their apparent solubility in aqueous buffer and vegetable oils of a series of 11 peptidomimetics varying with respect to chain length and degree of N-methylation were estimated. It was observed that the compounds in contact with water transformed into sticky, slowly dissolving semisolid materials. Based on these observations, the in vitro release behavior of selected peptide derivatives from oil solutions and in situ formed precipitates was investigated using a validated in vitro release model. Conclusion: The results of this investigation suggest that both types of oil-based drug delivery systems might constitute alternative sustained release formulation principles of such amorphous peptide derivatives for the intra-articular route of administration.