Extensive Studies on π-Stacking of Poly(3-alkylthiophene-2,5-diyl)s and Poly(4-alkylthiazole-2,5-diyl)s by Optical Spectroscopy, NMR Analysis, Light Scattering Analysis, and X-ray Crystallography

Abstract

Stacking of poly(3-alkylthiophene)s P3RThs and poly(4-alkylthiazole)s P4RTzs has been studied. Light scattering analysis indicates that head-to-tail (HT) type HT-P3HexTh (R = n-C6H13) gives a degree of depolarization (ρv) of 0.26 in CHCl3, which reveals that HT-P3HexTh takes a stiff structure even in the good solvent. Addition of CH3OH to CHCl3 solutions of HT-P3HexTh and head-to-head (HH) type HH-P4HepTz (R = n-C7H15) leads to π-stacking of the polymer molecules to form stable colloidal particles. The light scattering analysis of the colloidal solution of HT-P3HexTh in a 2:1 solution of CHCl3 and CH3OH reveals that HT-P3HexTh is aggregated in a parallel style. Results of filtration experiments using membranes with 0.20 and 0.02 μm pores agree with the degree of the aggregation. P3HexThs with irregular structures (P3HexTh (Fe) and P3HexTh (Ni) with HT/HH ratios of about 7/3 and 1/2, respectively) show a weaker trend to aggregate; however, P3HexTh (Fe) is considered to stack in a surface region of a stretched poly(ethylene terephthalate) PET film. A dichroism observed with the stretched PET film indicates that the π−π* absorption as well as photoluminescence of the stacked P3HexTh molecules have a transition moment along the direction of the polymer main chain. X-ray diffraction analysis of HT-P3RThs and HH-P4RTzs reveals that they take a face-to-face stacked structure with an end-to-end packing mode, except for HT-P3MeTh (R = Me). HT-P3MeTh forms a face-centered lattice with an interlayer distance of 3.51 Å. An alternative copolymer of bithiazole and 4,4‘-dibutylbithiazole is packed in an interdigitation mode. At temperatures below 0 °C, the HT-P3HexTh molecules are π-stacked in CHCl3, and the 1H NMR spectrum shows a severe magnetic effect on the thiophene ring. Solid 13C NMR data are also consistent with the π-stacking.

Synthesis and Characterization of Poly(3-hexylthiophene)-b-Polystyrene for Photovoltaic Application

“…All the spectra exhibit similar profile with maximum absorption wavelength at 560 nm. Both thermal and solvent annealing treatments provide a slight increase in absorbance at 607 nm, derived from the strong intermolecular interaction indicating the high crystallizability of the P3HT chains [27]. Therefore, the author can conclude that the the presence of PS block does not interfere with the stacking of the P3HT block .…”

Self-assembly of rod-coil block copolymers from weakly to moderately segregated regimes

“…The rod-coil block copolymer case is by far more complex, as liquid crystalline behaviour is induced by the presence of a rigid block in the block copolymer backbone, which can compete with or even dominate the classical microseparation arising from the positive enthalpy of mixing of the two different blocks. Further degrees of complexity in self-assembly of rod-coil block copolymer systems arise from intermolecular forces frequently occurring among rod-like polymers: in the cases of rod polymers realized by alpha-helices secondary structures in polypeptides, H-bonding can arise in between contiguous rods; similarly, in π-conjugated polymer rods, π-π interactions may form among closely packed rods [16][17][18]. Both types of intermolecular forces are expected to greatly affect the phase separation mechanisms.…”

Synthesis and properties of two novel regioregular conjugated polythiophenes with side-chain containing different substituted end groups

“…These data indicate the efficient π stacking and intermolecular interactions occurred in the film. In comparison with the absorption spectra of the polymer solutions in chloroform, the visible absorptions become red-shifted, similar to the case of poly(3-hexylthiophene) where a π-stacked structure in the solid state formed [22]. For P3BLMT, the visible absorption peak of film red-shifted by 21 nm from 464 to 485 nm in comparison with its chloroform solution.…”