Π-conjugated Monomers Research Articles

Controlled Supramolecular Polymerization via Bioinspired, Liquid-Liquid Phase Separation of Monomers.

Dynamic supramolecular assemblies, driven by noncovalent interactions, pervade the biological realm. In the synthetic domain, their counterparts, supramolecular polymers, endowed with remarkable self-repair and adaptive traits, are often realized through bioinspired designs. Recently, controlled supramolecular polymerization strategies have emerged, drawing inspiration from protein self-assembly. A burgeoning area of research involves mimicking the liquid-liquid phase separation (LLPS) observed in proteins to create coacervate droplets and recognizing their significance in cellular organization and diverse functions. Herein, we introduce a novel perspective on synthetic coacervates, extending beyond their established role in synthetic biology as dynamic, membraneless phases to enable structural control in synthetic supramolecular polymers. Drawing parallels with the cooperative growth of amyloid fibrils through LLPS, we present metastable coacervate droplets as dormant monomer phases for controlled supramolecular polymerization. This is achieved via a π-conjugated monomer design that combines structural characteristics for both coacervation through its terminal ionic groups and one-dimensional growth via a π-conjugated core. This design leads to a unique temporal LLPS, resulting in a metastable coacervate phase, which subsequently undergoes one-dimensional growth via nucleation within the droplets. In-depth spectroscopic and microscopic characterization provides insights into the temporal evolution of disordered and ordered phases. Furthermore, to modulate the kinetics of liquid-to-solid transformation and to achieve precise control over the structural characteristics of the resulting supramolecular polymers, we invoke seeding in the droplets, showcasing living growth characteristics. Our work thus opens up new avenues in the exciting field of supramolecular polymerization, offering general design principles and controlled synthesis of precision self-assembled structures in confined environments.

Degradable π-Conjugated Polymers.

The integration of next-generation electronics into society is rapidly reshaping our daily interactions and lifestyles, revolutionizing communication and engagement with the world. Future electronics promise stimuli-responsive features and enhanced biocompatibility, such as skin-like health monitors and sensors embedded in food packaging, transforming healthcare and reducing food waste. Imparting degradability may reduce the adverse environmental impact of next-generation electronics and lead to opportunities for environmental and health monitoring. While advancements have been made in producing degradable materials for encapsulants, substrates, and dielectrics, the availability of degradable conducting and semiconducting materials remains restricted. π-Conjugated polymers are promising candidates for the development of degradable conductors or semiconductors due to the ability to tune their stimuli-responsiveness, biocompatibility, and mechanical durability. This perspective highlights three design considerations: the selection of π-conjugated monomers, synthetic coupling strategies, and degradation of π-conjugated polymers, for generating π-conjugated materials for degradable electronics. We describe the current challenges with monomeric design and present options to circumvent these issues by highlighting biobased π-conjugated compounds with known degradation pathways and stable monomers that allow for chemically recyclable polymers. Next, we present coupling strategies that are compatible for the synthesis of degradable π-conjugated polymers, including direct arylation polymerization and enzymatic polymerization. Lastly, we discuss various modes of depolymerization and characterization techniques to enhance our comprehension of potential degradation byproducts formed during polymer cleavage. Our perspective considers these three design parameters in parallel rather than independently while having a targeted application in mind to accelerate the discovery of next-generation high-performance π-conjugated polymers for degradable organic electronics.

Spatiotemporal dynamics of supramolecular polymers by in situ quantitative catalyst-free hydroamination.

Implementing chemical reactivity into synthetic supramolecular polymers based on π-conjugated molecules has been of great interest to create functional materials with spatiotemporal dynamic properties. However, the development of an in situ chemical reaction within supramolecular polymers is still in its infancy, because one needs to design optimal π-conjugated monomers having excellent reactivity under mild conditions possibly without byproducts or a catalyst. Herein we report the synthesis of a supramolecular polymer based on ethynyl core-substituted naphthalenediimide (S-NDI2) molecules that react with various amines quantitatively in a nonpolar solvent, without a catalyst, at 298 K. Most interestingly, the in situ reaction of the S-NDI2 supramolecular polymer with a linear aliphatic diamine proceeded much faster than the homogeneous reaction of a monomeric naphthalenediimide with the same diamine, affording diamine-linked S-NDI2 oligomers and polymers. The acceleration of in situ hydroamination was presumably due to rapid intra-supramolecular cross-linking between ethynyl and amino groups fixed in close proximity within the supramolecular polymer. Such intra-supramolecular cross-linking did not occur efficiently with an incompatible diamine. The systematic kinetic studies of in situ catalyst-free hydroamination within supramolecular polymers provide us with a useful, facile and versatile tool kit for designing dynamic supramolecular polymeric materials based on electron-deficient π-conjugated monomers.

Tricomponent Supramolecular Multiblock Copolymers with Tunable Composition via Sequential Seeded Growth.

Synthesis of supramolecular block co-polymers (BCP) with small monomers and predictive sequence requires elegant molecular design and synthetic strategies. Herein we report the unparalleled synthesis of tri-component supramolecular BCPs with tunable microstructure by a kinetically controlled sequential seeded supramolecular polymerization of fluorescent π-conjugated monomers. Core-substituted naphthalene diimide (cNDI) derivatives with different core substitutions and appended with β-sheet forming peptide side chains provide perfect monomer design with spectral complementarity, pathway complexity and minimal structural mismatch to synthesize and characterize the multi-component BCPs. The distinct fluorescent nature of various cNDI monomers aids the spectroscopic probing of the seeded growth process and the microscopic visualization of resultant supramolecular BCPs using Structured Illumination Microscopy (SIM). Kinetically controlled sequential seeded supramolecular polymerization presented here is reminiscent of the multi-step synthesis of covalent BCPs via living chain polymerization. These findings provide a promising platform for constructing unique functional organic heterostructures for various optoelectronic and catalytic applications.

Porphyrin Nanowire Bundles for Efficient Photoconductivity, Photoemission, and Generation of Singlet Oxygens toward Photodynamic Therapy

Energy released from an accelerated high-energy single/cluster particle triggers solid-state polymerization and crosslinking reactions of porphyrin-based π-conjugated monomers within a nm-scaled 1-...

Electropolymerized Porous Conjugated Polymer Film as an Electrode for a Stable, High Energy Density Thin Film Asymmetric Supercapacitor

A novel π-conjugated monomer tert-butyl 3,8-di([2,2′-bithiophen]-5-yl)-6- oxophenanthridine-5(6H)-carboxylate (PNBTH-Boc) with a labile side chain was synthesized. The monomer was electropolymerize...

Substituent effects on fluorene-based linear supramolecular polymerizsation

ABSTRACTTwo supramolecular systems were constructed based on fluorene-based π-conjugated monomers with or without spiro structures, respectively, and their self-assemble behaviour and optical properties were investigated. Concentration-dependent 1H NMR and viscosity measurements indicated a transition from cyclic or oligomeric species at low concentrations to linear supramolecular polymers at high concentrations in the system without spiro structures. In contrast, the formation of cyclic species is minimised and not observed in the system with spiro structures.

Rhodium‐Catalyzed Stitching Polymerization of 1,5‐Hexadiynes and Related Oligoalkynes

A new mode of polymerization, rhodium-catalyzed stitching polymerization, has been developed for the synthesis of π-conjugated polymers with bridged repeating units from nonconjugated 1,5-hexadiynes containing both terminal and internal alkyne moieties as monomers. The polymerization proceeded smoothly with a high degree of stitching efficiency under mild conditions, and 1,5,9-decatriyne and 1,5,9,13-tetradecatetrayne monomers could also be employed. The present polymerization strategy would be particularly beneficial for the synthesis of polymers consisting of a repeating unit that is difficult to prepare as a stable monomer because it does not require the use of a preformed bridged π-conjugated monomer.

Investigation of Fluorine Atom Effect on Benzothiadiazole Acceptor Unit in Donor Acceptor Donor Systems

Synthesis of two new π-conjugated monomers containing fluorine substituted benzothiadiazoles as acceptor units and 3,4-ethylenedioxythiophene (EDOT) as donor unit was accomplished by facilitating Stille cross-coupling reactions (4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-5-fluorobenzo[c][1,2,5]thiadiazole (E2BTD-F) and 4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-5,6-difluorobenzo[c][1,2,5] thiadiazole (E2BTD-2F)). NMR and HRMS spectra of newly synthesized compounds are in agreement with the structures. To compare fluorine substitution effects, non-fluorinated analogue (4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)benzo[c][1,2,5]thiadiazole (E2BTD)) was also synthesized. Besides a blue shift in their absorption spectra, an anodic shift was also noted in the oxidation potentials of both monomers with fluorine atom substitution on the acceptor unit. This was further confirmed by DFT calculations such that upon fluorine substitution EDOT donor units deviate from planarity. Electropolymerization of the monomers were achieved successfully via potentiodynamic polymerization method. A similar trend in optoelectronic properties was also observed for the polymer films as for the monomers.

Multidirectional proton-conducting membrane based on sulfonated big π-conjugated monomer into block copoly(ether sulfone)s

The R&D of proton exchange membrane (PEM) with high conductivity and excellent stability is still of significance for the next generation high power density PEM fuel cells. One irreconcilable challenge is that the high proton conductivity realized through high ion exchange capacity (IEC) strategy always gets along with poor membrane stability. To alleviate this contradiction, large-size planar 4,4’-(5,11-dihydroindolo[3,2-b]carbazole-6,12-diyl)diphenol (DCP) units with highly dense sulfonation were deliberately incorporated into block poly(ether sulfone)s to facilitate the formation of hydrophobic/hydrophilic nanophase-separated structure and multidirectional proton-conducting channels through strong intermolecular π-π interaction and ionic acid-base interaction. In fact, proton conductivity of our PEMs with an IEC of 1.52 mequiv g−1 is up to 248.2 mS cm−1 at 90 °C without compromising its mechanical properties. The novel multi-sulfonated poly(ether sulfone)s could give a guideline for the development of multidirectional proton-conducting membrane.

Evaluation of an external initiating Ni(ii) diimine catalyst for electron-deficient π-conjugated polymers

We have prepared, isolated, and evaluated the first Ni(ii) diimine catalyst able to externally initiate the Kumada catalyst transfer polymerization of an electron-deficient π-conjugated monomer.

Dibenzothiophene-thiophene hybrid electrochromic polymer: effect of media on electrosynthesis and optical properties

π-Conjugated monomer, namely 2,8-bis-(4-octoxythiophen-2-yl)-dibenzothiophene (DBT-3OctTh), containing dibenzothiophene moiety as the central unit and 3-octoxythiophene as the external unit have been synthesized via Stille coupling reaction. The monomer was obtained as white powder in a yield of 75 %. Its electropolymerization was comparatively investigated in different media (dichloromethane (DCM), propylene carbonate (PC), or boron trifluoride diethyl etherate (BFEE)), all using Bu4NPF6 as the electrolyte. In BFEE, DBT-3OctTh revealed the lowest onset oxidation potential (0.67 V vs. Ag/AgCl) than DCM (1.12 V) and PC (1.13 V), leading to a facile electrodeposition to prepare poly(2,8-bis-(4-octoxythiophen-2-yl)-dibenzothiophene) (PDBT-3OctTh) with less possibility occurring on the side reactions. Doping level was calculated to be 0.32 in DCM, 0.12 in BFEE, and 0.04 in PC, respectively. The structure and performances of as-prepared polymers were systematically studied by cyclic voltammetry and spectroelectrochemistry. Spectroelectrochemical analysis revealed that PDBT-3OctTh films prepared in these media all switched light grey in the neutral state whereas blue in the oxidized state. Further, the existence of polaron or/and bipolaron in the oxidation process demonstrated that PDBT-3OctTh was p-dopable.

Molecular Wiring Method Based on Polymerization or Copolymerization of an Insulated π-Conjugated Monomer

Abstract A new type of molecular wiring method was developed based on the polymerization or copolymerization of an insulated π-conjugated monomer between nanosized electrodes.

Synthesis of two novel acenaphthyl-quinoxaline based low-band gap polymers and its electrochromic properties

Two novel π-conjugated monomers, 8,11-bis(4-octyl-2-thienyl)-acenaphthyl-[1,2-b] quinoxaline (OTAQ) and 8,12-bis(4-octyl-2-thienyl)-acenaphthyl-[1,2,5]thiadiazolo[3,4,i]quinoxaline (OTATQ), were synthesized. These polymers contains on type electron donating unit 3-octylthiophene and two type of electron withdrawing unit that acenaphthyl-quinoxaline in OTAQ and acenaphthyl-thiadiazolo-quinoxaline in OTATQ, respectively. Electrochemical polymerization of the monomers were carried out in acetonitrile/dichloromethane soluvent mixture containing tetra-n-butylammonium hexafluorophosphate and electrochromic properties of polymers are described in this paper. Furthermore, the effects of structural difference on electrochemical redox behavior and spectroelectrochemical properties of the two resulting polymers were examined. The results showed that an anodic wave at +0.56 V vs Ag wire pseudo-reference electrode corresponding to the monomer OTAQ oxidation was observed, and an anodic wave at +0.91 V was observed in oxidation of OTATQ due to it contains stronger electron withdrawing unit in which contain thiadiazolo structure. The UV–vis-NIR spectra analysis revealed that the POTAQ film has two absorbance bands centered at 694 nm and longer than 1,600 nm and the POTATQ film has an absorbance at 1,014 nm, respectively. The band gaps of these polymers, defined as the onset of the absorption band at 694 nm for POTATQ and the absorption band at 1,014 nm for POTATQ, were determined as 1.06 eV for POTAQ and as 0.76 eV for POTATQ. The electrochromic results showed that the two polymer films revealed about 30 % optical contrast in the NIR region with low response time (5 s for POTAQ and 10 s for POTATQ).

Synthesis of functionalized insulated molecular wires by polymerization of an insulated π-conjugated monomer

A new method for the synthesis of an insulated π-conjugated monomer was developed via the sequential self-inclusion followed by the elongation of the π-conjugated unit. The monomer was utilized in the synthesis of stimuli-responsive insulated molecular wires.

Donor–acceptor type neutral green polymers containing 2,3-di(5-methylfuran-2-yl) quinoxaline acceptor and different thiophene donors

A series of donor–acceptor type π-conjugated monomers containing quinoxaline moiety in the backbone as the acceptor unit and thiophene derivatives as the donor unit have been synthesized by Stille coupling. The effects of different donor substituents on the polymer’ electrochemical and spectroelectrochemical properties were examined. 2,3-di(5-methylfuran-2-yl)-5,8-bis(2-(3,4-ethylenedioxythiophene)) quinoxaline (MFEQ) with strong electron-donating ethylenedioxy group has a lower oxidation potential than that of 2,3-di(5-methylfuran-2-yl)-5,8-bis(2-thienyl) quinoxaline (MFTQ) and 2,3-di(5-methylfuran-2-yl)-5,8-bis(2-(3-methoxythiophene)) quinoxaline (MFMQ). The optical properties of polymers are also tuned due to different strength of donor units. Both PMFEQ and PMFMQ exhibit a green color in the neutral state, while PMFTQ with two absorption bands at 360nm and 558nm is purple. As donor–acceptor type materials, all three polymers can be both p- and n-doped, with fast response time, narrow band gap and high optical contrast (ΔT%).

Naphthodifuranone-Based Monomers and Polymers

The synthesis of new π-conjugated monomers and polymers containing 3,8-bisphenylnaphtho[2,1-b:3,4-b′]difuran-2,9-dione (1,10-NDF) units in the main chain is described. 1,10-NDF-monomer M1 (3,8-bis(4-bromophenyl)naphtho[2,1-b:3,4-b′]difuran-2,9-dione) was obtained upon condensation of 2,3-dihydroxy-naphthalene and 4-bromo-mandelic acid followed by oxidation with nitrobenzene. M2 (3,8-bis(4-(5-bromo-4-octylthiophen-2-yl)phenyl)naphtho[2,1-b:3,4-b′]difuran-2,9-dione) was obtained upon Stille coupling of 4-n-octylthiophen-2-yl-trimethylstannane and M1 followed by bromination of the thiophene groups with NBS. The X-ray structure analysis of M1 indicated a dihedral angle of 42–45° between the lactam phenyl groups and the NDF core, and weak intermolecular π–π stacking with a distance of 3.36 Å between the chromophors. A HOMO–LUMO calculation of M1 indicates an electron transfer from the phenyl groups to the NDF core upon excitation. Polymers were obtained upon palladium-catalyzed Suzuki and Stille coupling reactions of M1 and M2 with 2,2-(9,9-dioctyl-9H-fluorene-2,7-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) and 2,5-bis(tributylstannyl)thiophene. The polymers exhibit broad absorption bands with maxima between 508 and 564 nm and tails reaching up to 1057 nm in thin films, and high extinction coefficients of 1.1 × 104 to 3.9 × 104 L mol–1 cm–1. Band gaps are between 1.45 to 1.63 eV. Photoirradiation studies indicate that the polymers are extremely stable to UV and visible light.

Synthesis of π-Conjugated 2,2:6′,2″-Terpyridine-Substituted Oligomers Based on 3,4-Ethylenedioxythiophene

Dissymmetric π-conjugated monomers and oligomers incorporating 3,4-ethylenedioxythiophene (EDOT) units and bearing terpyridine end groups were synthesized in good yields through Vilsmeyer-Haak formylation followed by a reaction with 2-acetylpyridine in basic media or, for the longest oligomers, direct C-H bond arylation. They have a low HOMO-LUMO gap and are easily oxidized at low potentials. Upon complexation with cobalt(II) and iron(II) they yield new hybrid materials that can be used in various applications ranging from photovoltaics to spintronics.

Accelerating Ni(ii) precatalyst initiation using reactive ligands and its impact on chain-growth polymerizations

Nickel(II) complexes with varying reactive ligands, which were designed to selectively accelerate the initiation rate without influencing the propagation rate in the chain-growth polymerization of π-conjugated monomers, were investigated. Precatalysts with electronically varied reacting groups led to faster initiation rates and narrower molecular weight distributions. Computational studies revealed that the reductive elimination rates are largely modulated by the ability of the two reacting arenes to stabilize the increasing electron density on the catalyst during reductive elimination. Overall, these studies provide insight into a key mechanistic step of cross-coupling reactions (reductive elimination) and highlight the importance of initiation in controlled chain-growth polymerizations.

Tailoring the optoelectronic properties of donor–acceptor–donor type π-conjugated polymers via incorporating different electron-acceptor moieties

Syntheses of donor–acceptor–donor type of π-conjugated monomers were performed to examine the effect of the acceptor units' strength on the electrochemical and optoelectrochemical properties of the resulting monomer and polymer. Palladium catalyzed Stille cross-coupling reaction of an organotin reagent with an organic electrophile was used for the synthesis of target monomers, 5,8-bis(4-hexylthiophen-2-yl)-2-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-3-(2,3-dihydrobenzo[b][1,4]dioxin-7-yl)quinoxaline (DBQHT) and 10,13-bis(4-hexylthiophen-2-yl)dibenzo[a,c]phenazine (PHEHT).The presence of the strong electron-donating ethylenedioxy groups on pendant phenyl rings increased electron density on DBQHT, thus the oxidation potential of DBQHT shifts to a lower value than that of PHEHT. The π–π* absorption maximum of PPHEHT was about 40nm red-shifted compare to that of PDBQHT, which can be attributed to the increase of the effective conjugation and coplanarity of PPHEHT relative to PDBQHT via using phenanthrene fused quinoxaline unit as the acceptor. The electronic band gap of polymer, defined as the onset of the π–π* transition, is found to be 1.65eV for PPHEHT and 1.82eV for PDBQHT. Both polymer films showed multi-color electrochromism. PDBQHT can be switched between a red neutral state and a green oxidized state with two intermediate states; purple and brown. PPHEHT also shows multicolored electrochromic behavior with three distinct states: a blue neutral state, a gray intermediate state, and a green oxidized state.