Influence of the Supramolecular Organization on the Magnetic Properties of Poly(3-alkylthiophene)s in Their Neutral State

Abstract

b S Supporting Information ' INTRODUCTIONFor almost three decades, π-conjugated polymers have been explored extensively. Besides their optical, electrical, and electronic properties, 1 also the magnetic behavior has been investigated, albeit to a lesser extent. In order for an organic compound to exhibit ferromagnetism, unpaired electrons (spins) should be present. Mostly, spins are intrinsic 2À4 to the material or introduced as radicals, carbenes, or by oxidation. 2,3,5 A second requirement is a pathway by which unpaired spins can mutually interact (spin coupling). 6 In this point of view, a conjugated π-system is ideal to act as a (ferro)magnetic linker between different spins. However, the substitution pattern and the connectivity are crucial parameters to have ferromagnetic spin coupling, aligning spins in the same direction of an external magnetic field. 7 Quite some "high-spin" molecules, 8,9 oligomers, 10 and polymers 11À14 have been reported based on this approach, and remarkable advances have been achieved.Besides the "high-spin" molecules, also some typical conjugated polymers were reported, showing magnetic behavior under very specific conditions. Typical examples are poly(aniline)s, 15À18 poly(pyrrole), 19 regioirregular poly(3-alkylthiophene)s, 20À24 and (substituted) poly(acetylene)s. 25 In all these examples, the materials were chemically or electrochemically doped, introducing spins (polarons). In contrast to these results, we have previously reported on the magnetic behavior of neutral (undoped) poly(thiophene)s carrying an alkyl, alkoxy, or alkylthio side chain. 26 A comparison of the ESR and SQUID data reveals the presence of (at least) two spin systems. A first electron spin system gives rise to a paramagnetic behavior. A second spin system (of which the origin is unknown) results in a superparamagnetic behavior at 300 K and (for most polymers) a ferromagnetic behavior at 5 K. The ESR-active system is not responsible for the ferromagnetic behavior at 5 K. This has been concluded from the fact that it exhibits a paramagnetic behavior and that there is a large discrepancy between the number of spins (S = 1/2), determined by ESR, and the number of Bohr magnetons (magnetic moment of an electron) measured by SQUID magnetometry. Concerning the presence of ferromagnetism and the coercivity, it was found that polymers in which strong π-interactions between stacked polymer chains are present show the highest coercivity. Therefore, it can be hypothesized that these π-interactions determine the ferromagnetic behavior (coercivity).In this article, the influence of supramolecular organization and π-stacking of a chiral substituted, head-to-tail coupled poly-(3-alkylthiophene) (HT-P3AT) on its magnetic behavior is investigated ( Figure 1). First, since aggregate formation is influenced by the molar mass of these polymers, samples with different molar masses were prepared by fractionation. Differences in their ABSTRACT: The influence of the supramolecular behavior on the magnetic properties of head-to-tail ...

Vapour-Induced Liquid Crystallinity and Self-Recovery Mechanochromism of Helical Block Copolymer

“…The PDI value was relatively high because the GRIM reaction usually proceeds in living fashion. The high value of PDI is probably caused by the broad polydispersity nature of Ni-teriminated PTh macroinitiator as reported in the literature 26 . PTh- b -PPI was thoroughly characterised by NMR, IR, UV, CD, and PL (Figures S1 and S2, Fig.…”

“…This large red-shift indicates conformational change of the PTh block into J -aggregation states with planar main-chain conformation. The spectra strongly support formation of PTh- b -PPI aggregation driven by π-π interaction between the PTh blocks 26 . PL spectra (Fig.…”

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

“…(B)]. As mentioned previously, the absorption spectrum of aggregated P3AT consists of three chromophores. One band [Fig.…”

“…In all these cases, the materials were chemically or electrochemically doped, introducing spins (polarons). In contrast to these results, we have previously reported on the magnetic behavior of neutral (undoped) poly(thiophene)s carrying an alkyl, alkoxy, or alkylthio sidechain . The samples were examined by ESR spectroscopy and SQUID magnetometry.…”

Asymmetric electrochemical polymerization in cholesteric liquid crystalline media: Effect of isomeric structures of chiral inducers containing bornyl group

“…Highly-ordered structure in polymers has a great advantage for obtaining macroscopic properties such as ionic conduction [1], mechanical properties [2] and characteristic morphorogies [3]. Many approaches for controlling highly-ordered structure of conjugated polymers have been examined [4][5][6][7]. Highly-ordered conjugated polymers have attraction in their energy transferring and optical properties [8][9][10], forming mesoscopically characteristic structure such as lamellae [11], nanofibers [12] and one-handed helical aggregations [13].…”