High-spin Polymers Research Articles

Thermoelectric Performance in Triplet-Ground-State Polymer Intrinsically Boosted by Enhanced Proquinoidal Characteristic.

Over the past decade, polymer thermoelectric materials featuring flexibility, lightness, and bio-friendliness have been paid increasing attention as promising candidates for waste heat recovery and energy generation. For a long time, the dominant approach to optimizing the thermoelectric performance of most organic materials is chemical doping, which, however, is not always ideal for practical applications due to its tendency to involve intricate processing procedure and trigger material and device instability. Currently, the pursuit of single-component neutral thermoelectric materials without exogenous doping presents a compelling alternative. In this work, we designed and synthesized a high-spin polymer material, PBBT-TT, by simultaneously employing thieno[3,4-b]thiophene (TbT) and benzo[1,2-c : 4,5-c']bis[1,2,5]thiadiazole (BBT) units with pronounced proquinoidal characteristics, its analogue, PBBT-T to demonstrate the effect of the TbT unit was also synthesized. The results indicate that because of the enhanced quinoidal resonance, increased spin density and strong intermolecular antiferromagnetic coupling, PBBT-TT exhibits high intrinsic electrical conductivity and Seebeck coefficient, which showcases an outstanding power factor of 26.1 μW m-1 K-2 without doping. This achievement surpasses other neutral organic conjugated polymer and radical conductors, and is even comparable to some typical early-stage doped polymers. Notably, PBBT-TT exhibits remarkable ambient stability, retaining its initial thermoelectric performance over a 120-day period. Our finding demonstrates that modulating the intermolecular spin interactions in open-shell polymers through the introduction of strong proquinoidal units is an effective strategy for the development of doping-free, intrinsically high-performance polymer thermoelectric materials.

A high-spin s-triazine linked fluorenyl radical polymer.

The syntheses of high-spin organic polymers have been a daunting task due to the highly reactive nature of organic radicals, especially when they are ferromagnetically coupled. In this paper, we report our approach to obtain high-spin organic polymers, in which a reasonably stable fluorenyl radical was employed as the primary radical unit, and s-triazine serves as the connector that facilitates ferromagnetic coupling between them. Initially, the diamagnetic polymer precursor was synthesized by cyclotrimerization of a cyano-monomer. Subsequently, the high-spin polymers were obtained by oxidizing corresponding anionic polymers using O2 (6) or I2 (7). The temperature-dependent magnetic moments, and field-dependent magnetization data obtained from SQUID measurements revealed ferromagnetic couplings between primary radical units, with coupling J = 7.5 cm-1 and 38.6 cm-1. The percentages of primary unit in the radical form are 29%, and 47% for 6 and 7, respectively. Notably, this marks the first reported instance of a high-spin fluorenyl radical polymer exhibiting ferromagnetic coupling.

Elucidating the structure of donor-acceptor conjugated polymer aggregates in liquid solution.

High-spin donor-acceptor conjugated polymers are extensively studied for their potential applications in magnetic and spintronic devices. Inter-chain charge transfer among these high-spin polymers mainly depends on the nature of the local structure of the thin film and π-stacking between the polymer chains. However, the microscopic structural details of high-spin polymeric materials are rarely studied with an atomistic force field, and the molecular-level local structure in the liquid phase remains ambiguous. Here, we have examined the effects of oligomer chain length, side chain, and processing temperature on the organization of the high-spin cyclopentadithiophene-benzobisthiadiazole donor-acceptor conjugated polymer in chloroform solvent. We find that the oligomers display ordered aggregates whose structure depends on their chain length, with an average π-stacking distance of 3.38 ± 0.03 Å (at T = 298 K) in good agreement with the experiment. Also, the oligomers with longer alkyl side chains show better solvation and a shorter π-stacking distance. Furthermore, the clusters grow faster at higher temperature with more ordered aggregation between the oligomer chains.

High-mobility semiconducting polymers with different spin ground states

Organic semiconductors with high-spin ground states are fascinating because they could enable fundamental understanding on the spin-related phenomenon in light element and provide opportunities for organic magnetic and quantum materials. Although high-spin ground states have been observed in some quinoidal type small molecules or doped organic semiconductors, semiconducting polymers with high-spin at their neutral ground state are rarely reported. Here we report three high-mobility semiconducting polymers with different spin ground states. We show that polymer building blocks with small singlet-triplet energy gap (ΔES-T) could enable small ΔES-T gap and increase the diradical character in copolymers. We demonstrate that the electronic structure, spin density, and solid-state interchain interactions in the high-spin polymers are crucial for their ground states. Polymers with a triplet ground state (S = 1) could exhibit doublet (S = 1/2) behavior due to different spin distributions and solid-state interchain spin-spin interactions. Besides, these polymers showed outstanding charge transport properties with high hole/electron mobilities and can be both n- and p-doped with superior conductivities. Our results demonstrate a rational approach to obtain high-mobility semiconducting polymers with different spin ground states.

ChemInform Abstract: Polymers for Electronics and Spintronics

AbstractReview: <550 refs.

Polymers for electronics and spintronics

This critical review is devoted to semiconducting and high spin polymers which are of great scientific interest in view of further development of the organic electronics and the emerging organic spintronic fields. Diversified synthetic strategies are discussed in detail leading to high molecular mass compounds showing appropriate redox (ionization potential (IP), electron affinity (EA)), electronic (charge carrier mobility, conductivity), optoelectronic (electroluminescence, photoconductivity) and magnetic (magnetization, ferromagnetic spin interactions) properties and used as active components of devices such as n- and p-channel field effect transistors, ambipolar light emitting transistors, light emitting diodes, photovoltaic cells, photodiodes, magnetic photoswitches, etc. Solution processing procedures developed with the goal of depositing highly ordered and oriented films of these polymers are also described. This is completed by the description of principal methods that are used for characterizing these macromolecular compounds both in solution and in the solid state. These involve various spectroscopic methods (UV-vis-NIR, UPS, pulse EPR), electrochemistry and spectroelectrochemistry, magnetic measurements (SQUID), and structural and morphological investigations (X-ray diffraction, STM, AFM). Finally, four classes of polymers are discussed in detail with special emphasis on the results obtained in the past three years: (i) high IP, (ii) high |EA|, (iii) low band gap and (iv) high spin ones.

Magnetic properties of very-high-spin organic π-conjugated polymers based on Green’s function theory

Magnetic properties of two very-high-spin organic pi-conjugated polymers have been investigated theoretically by means of the many-body Green's function method with random phase approximation. The polymers are designed with a large density of cross-links and alternating connectivity of radical modules with unequal spin quantum numbers (S), macrocyclic S=2 or 3, and cross-linking S=1/2 modules, which permit large net S values for either antiferromagnetic or ferromagnetic exchange coupling between the modules. The numerical results reveal that, ascribing to the zero-temperature spin fluctuations, the sublattice magnetizations of the two polymers are both smaller than their classical spin values and the ground-state magnetizations of them are also smaller than their predicted values in the antiferromagnetic exchange coupling case. However, these magnetic behaviors do not occur in the ferromagnetic exchange coupling case. On the basis of our synthesis of the temperature dependence of the magnetic susceptibility multiplied by temperature, and through comparing the theoretical results with the experimental measurements, it is concluded that the magnetic exchange couplings between the modules within the two high-spin polymers should be ferromagnetic exchange couplings, which are consistent with other theoretical results drawn from the investigations into the ground-state properties of the two organic polymers.

Disjoint and coextensive amminium radical cations: a general problem in making amminium radical cation based high-spin polymers

A two-electron oxidation of N, N, N′, N′-tetrakis(2-methoxyphenyl)-1,3-diaminobenzene 12 gives the diradical dication 12 2 + , which is an aza analogue of the Schlenk hydrocarbon and, like the Schlenk hydrocarbon, has a triplet ground state. However, an attempt to produce pentuplet tetraradical tetracations by extending the same ferromagnetic spin-coupling motif in a linear or a cyclic fashion was unsuccessful. Two-electron oxidations to give disjoint diradical dications (in which the charges and spins are spatially separated) are relatively easy but it proved impossible to remove the third and fourth electrons. This would require generation of coextensive radical ions in which the charges and spin distributions overlap. The results obtained with these model oligomers illustrate what is a general problem in the creation of high-spin polymers in which the spin-bearing centres are amminium radical cations. Strong ferromagnetic spin-coupling depends on the formation of coextensive rather than disjoint radical cations but the formation of coextensive radical cations with strong ferromagnetic coupling involves a large additional coulombic penalty.

Ferromagnetic spin-coupling 4,4″-through metaterphenyl: models for high-spin polymers

Model diradical dications have been synthesised which have the 4,4″-through metaterphenyl spin-coupling pathway found in arylamine high-spin polymers. In the model triplet diradical dication derived by a two-electron oxidation of N,N,N″,N″-tetrakis(4-tert-butyl-2-methoxyphenyl)-3,3″-dimethoxy[1,1′;3′,1″]terphenyl-4,4″-diamine the separation between the triplet and singlet states was found to be 0.083 kcal mol−1. This value is close to that predicted on the basis that the energy difference should be proportional to the product of the spin densities in the ‘common’ ring (the ring in which the two spin densities overlap). This is an important principle in the design of new high-spin polymers.

Organic spin clusters: annelated macrocyclic polyarylmethyl polyradicals and a polymer with very high spin S=6-18.

Synthesis and magnetic studies of annelated macrocyclic polyradicals and a related high-spin polymer with macrocyclic repeat units are described. Polyarylmethyl polyether precursors to the polyradicals and the related polymer are prepared by using Negishi cross-coupling of difunctionalized calix[4]arene-based macrocycles. The three lowest homologues, with high degree of monodispersity, are tetradecaether (14-ether) 3-(OCH(3))(14), octacosaether (28-ether) 4-(OCH(3))(28), and dotetracontaether (42-ether) 5-(OCH(3))(42), in which 2, 4, and 6 calix[4]arene-based macrocycles are annelated to the center macrocycle, respectively. The evidence for their annelated structures (ladder connectivities) is based upon FAB-MS and the (1)H NMR based end-group analysis. The absolute masses (4-12 kDa) were determined by FAB-MS and GPC/MALS. Small angle neutron scattering (SANS) provides the radii of gyration of 1.7, 2.0, and 3.2 nm for 4-(OCH(3))(28), 5-(OCH(3))(42), and polymer 6-(OCH(3))(n), respectively. The corresponding polyarylmethyl polyradicals 3 and 4, and polymer 6 possess average values of S approximately 6-7, S approximately 10, and S approximately 18, respectively, as determined by SQUID magnetometry and numerical fits to linear combinations of Brillouin functions. The quantitative values of magnetization at saturation and of magnetic susceptibilities indicate that about 40-60 % of unpaired electrons are present at low temperatures (T=1.8-5 K). For polyradical 3, the variable temperature magnetic data are fit to the Heisenberg Hamiltonian based model. The variable magnetic field data at low temperatures are also fit to a percolation-based model for organic spin cluster, with random distribution of chemical defects, and ferromagnetic versus antiferromagnetic couplings, providing quantitative agreement between the experiment and the theory. For polyradical 3 (with S approximately 6-7), annealing at room temperature for 0.5 h leads to a polyradical with S approximately 5.

Structure and properties of non-classical polymers. Part XIII. 1-D high-spin polymers with out of chain radical sites

The magnetic properties of some classes of 1-D high-spin alternant organic polymers were studied theoretically. The objects considered in this paper are π-conjugated linear polymers bearing radical groups that are attached to the π-conjugated backbone to yield non-classical (non-Kekule) structures (pendant-type polyradicals). The polymers have similar energy spectra: a large energy gap in the middle of which a half-filled band (HFB) of degenerate MOs is situated. In all cases the π-electrons within the HFB are ferromagnetically coupled with the main contribution of the direct (Coulomb) exchange. However, the different topologies and geometries of the polymers determine the essentially different magnitude of the magnetic coupling. Especially the high-spin derivatives of polymers built up from poly(acene) cata-condensed chains (ribbons) are characterized by very large values of the effective exchange integral which increases drastically with increasing the number of the poly(acene) ribbons.

Density functional study of intramolecular ferromagnetic interaction through m-phenylene coupling unit. III. Possibility of high-spin polymer

Because it has been well-known that the effective exchange interaction of spins is much larger within a molecule than between molecules, it is very important to design high-spin polymers linking high-spin molecules with each other as a constituent unit to obtain molecule-based ferromagnetic materials with high transition temperature. Experimental efforts to synthesize such polymers extended in one- or two-dimensions have been made in recent years while theoretical treatment of infinite polymers has been behind in the sense that no study of electronic and magnetic structure calculations by ab initio periodic approaches exists until now. We examined the magnetic properties in m-phenylene and related molecules with organic radicals by density functional and molecular orbital methods as monomer units of high-spin polymers in Part I and Part II of this series, since it has already been confirmed experimentally and theoretically that m-phenylene coupling unit leads to the ferromagnetic coupling between spins. In Sec. III, we examine the possibility of ferromagnetic polymers in which organic radicals are arranged thorough m-phenylene bridge periodically in one dimension. For this purpose, ab initio crystal orbital methods based on density functional and Hartree–Fock approximations are employed for m-phenylene polymers with four species of C, CH, N, and NH+ radical groups as spin sources. It is shown that these polymers have the high-spin ground states and the density functional approaches can yield reasonable results which are comparable with the experiment. Implications of the calculated results are also discussed in relation to ferromagnetic polymers with different coupling units.

Very High-Spin Organic Polymer: π-Conjugated Hydrocarbon Network with Average Spin of S ≥ 40

Very High-Spin Organic Polymer: π-Conjugated Hydrocarbon Network with Average Spin of <i>S</i> ≥ 40

Ground State Spin Multiplicity of Cation Diradicals Derived from Pyrroles Carrying Nitronyl Nitroxide

Pyrroles substituted by nitronyl nitroxide (1–3) have been prepared and the ground state multiplicity of their cation diradicals have been examined. The triplet was found to be the ground state for 2+., 3+., although the triplet signal was not observed for 1+. The ground state spin multiplicity of these cation diradicals was rationalized in terms of the exchange interaction between unpaired electrons which reside SOMO and SOMO' of these species, respectively. A novel approach to polaronic high spin polymers obtained from 1,3-phenylene-bis(2′-1H-pyrrole) is also mentioned.

FT pulsed-ESR/electron spin transient nutation of hyperbranched polycationic organic high-spin polymers

As a novel electron magnetic resonance technique for the characterization of organic molecule-based magnets, an electron spin transient nutation method based on Fourier-transformed pulsed ESR spectroscopy was applied to polycationic organic polymers. The polymers are triphenylamine-based in the hyperbranched three-dimensional network with the unpaired electrons at the nitrogen cation sites. The FIDdetected nutation spectrum from one of the polymers exhibited several nutation-frequency components corresponding to high-spin species containing S=3. The static magnetic susceptibility of the polymer supported the high-spin ground state in the system under study. The present results demonstrate the potentialities of the charged high-spin polymers as well as the methodological advantage of nutation spectroscopy in identifying the spin multiplets of the molecule-based magnets in the frequency domain.

Ab initio MO study of m-phenylenediamine and 2,4-diamino-1,3,5-triazine dication diradicals

Ab initio MO calculations of m-phenylenediamine ( 1) and 2,4-diamino-1,3,5-triazine ( 2) dication diradicals, which are the model molecules of two possible high-spin polymers (poly( m-aniline) and poly(imino-1,3,5-triazinediyl) cation radicals), have been carried out with the 6–31G * basis set at the ROHF, GVB and CASSCF levels. In accordance with qualitative MO considerations, the electronic structures of 1 2+ and 2 2+ were quite different from each other. In the planar C 2V geometry, the singlet-triplet splittings (ΔE S-T) of 1 2+ and 2 2+ were calculated to be 0.7 and 12.5 kcal/mol, respectively, at the CASPT2 level. m-1,3,5-triazinediyl is another effective ferromagnetic coupler for the aza-substituted systems.

P-Doped high spin polymers1

High spin polymers have been created from p-doping of networked polyaryl and polyarylamine polymers which were synthesized using the Pd0 mediated coupling reaction of aryl di- and tri-bromides with aryl bis- and tris-boronic acids. The doping procedures produce polyradical polycations in which (in the limit of 100% doping) each spin is coextensive in its spatial distribution with three neighbouring spins. Magnetic susceptibility studies show the expected ferromagnetic spin-coupling. In this respect the best of these systems is the polymer obtained by the Pd0 mediated coupling of 1,3-dibromo-5-tetradecylbenzene with tris(4-boronic acid-2-hexyloxyphenyl)amine which was subsequently p-doped with NO+BF4– . A Brillouin function fit to the field dependence of the magnetization of this doped polymer at 2 K corresponds to an average spin S of 5/2. The best levels of doping achieved so far are about 15% of the theoretical maximum. These are sufficient to demonstrate the genuine high-spin nature of these polymers but are well short of the ca. 70% percolation limit needed for bulk superparamagnetic or ferromagnetic behaviour. The low doping levels are attributed to steric rather than coulombic effects.

Disjoint and coextensive diradical diions

N,N,N′,N′- Tetraanisyl-3,3′-diaminobiphenyl and N,N,N′,N′-tetraanisyl- 3,4′-diaminobiphenyl have been synthesised and their oxidations studied by cyclic voltammetry and EPR spectroscopy. A two-electron oxidation of the former species gives a π system which is disjoint and oxidation of the latter gives a π system which is coextensive. Cyclic voltammetry is shown to be a useful tool for revealing the difference between the disjoint and coextensive π systems. The coulombic contribution to the difference between the half-wave potentials for the first and second oxidation steps (ωE), which measures the ‘hole–hole’ repulsion energy, was extracted by measuring ωE as a function of the relative permittivity of the medium. This was substantially greater in the coextensive case. Both diradical diions gave triplet EPR spectra. A comparison of the cyclic voltammetry of N,N,N′,N′-tetraanisyl- 3,4′-diaminobiphenyl and that of a high-spin polymer precursor with the same local topology showed that, in the oxidised polymer, the additional hole–hole repulsion energy associated with the coextensive spin–spin distribution is of the order of 0.1–0.2 V—a noticeable effect but not one large enough to explain the difficulties that have been encountered in achieving high doping levels in this and related high-spin polymers.

Ferromagnetic Interaction between Aminium Radical Centers through m-Phenylene and m-1,3,5-Triazinediyl.

Ab initio MO study (at the ROHF, GVB, and CASSCF levels) of m-phenylenediamine (1) and 2,4-diamino-1,3,5-triazine (2) dication diradicals, which are model molecules of two possible high-spin polymers, poly(m-aniline) and poly(imino-1,3,5-triazinediyl) cation radicals, is presented. On the basis of qualitative MO considerations, it was seen that the electronic structures of 1(2+) and 2(2+) differed considerably. The singlet-triplet splittings (DeltaE(S)(-)(T)) of 1(2+) and 2(2+) were calculated to be 0.7 and 12.5 kcal/mol, respectively, at the CASPT2 level. m-1,3,5-Triazinediyl is shown to be a strong ferromagnetic coupler for aza-substituted systems.

高分子科学最近の進歩 高スピンポリマー

高分子科学最近の進歩 高スピンポリマー