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 stretc...

Extensive studies on pi-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

Clarifying the changes in the physical behavior of flexible side chain substituted π-conjugated and other rodlike polymers continues to be an important research topic. For conducting polymers, this side chain addition, when coupled with controlled synthesis, has been shown to dramatically enhance key electronic properties and profoundly alter the macromolecular structures. 1-4 In particular, the ability to specify the extent of poly(3-alkylthiophene) (P3AT) chemical regularity, 4-6 with respect to side chain positioning, has increased the maximum observable conductivities as well as focused attention on the role that side chains play. Regioregular poly(3-dodecylthiophene) (R-P3DDT), with 98% head-to-tail (HT) coupling of the alkyl side chains along the backbone, has conductivities (when doped with an electron acceptor) up to 50 times those seen in the \" regioirregular \" counterpart (IR-P3DDT) having only 75% HT linkages. R-P3DDT, which contains a high proportion of insulating side chains, also exhibits conductivities up to twice those reported for the unsubsti-tuted parent polymer, polythiophene. There are other surprising features as well. P3AT's are also found to be thermo-and solvatochromic. 1,7 Many P3AT samples exhibit semicrystalline lamellar phases exhibiting a thermotropic transition to a liquid crystalline (LC) state. 8,9 While these mesophases may improve proces-sibility, they also have the potential for altering the electronic properties. Consequently, the full range of structure-property interrelationships that side chains impart to these polymers needs to be explored in order to realize their full potential and limitations. 10 The most prevalent crystal structure reported for P3AT's has been studied extensively. 8,9,11-13 These studies support a lamellar base structure in which parallel stacks of polymer main chains are separated by regions filled by the alkyl side chains (see inset of Figure 1). Each layer consists of stacked arrays of the main chains spaced 3.8 Å apart and sequentially displaced, along the skeletal c-axis direction, by one thiophene unit (c/2 or 3.9 Å), resulting in a staggered nesting of the side chains. Structure factor intensity calculations 9 support a model in which these side chains are strongly tilted at an angle such that this side chain nesting approximates a 4.5 Å hexagonal close packing in close correspondence to the average packing of pure alkanes or polyethylene. 14 Overlap (interdigitation) between side chains in neighboring stacks is minimal although there can be ordering of the side chains across the layer-layer interface. 9 Additional phases are described 15-18 but the full structural details are incomplete. In this communication …

Evidence of a Novel Side Chain Structure in Regioregular Poly(3-alkylthiophenes)

The thermodynamic phase behavior and the morphology in thin films of poly(3-hexylthiophene) (P3HT) has been studied using calorimetry, X-ray scattering, and scanning force microscopy (AFM). Around 225 °C a phase transition from the crystalline state to a layered, liquid crystalline structure occurs in regioregular P3HT, while the regiorandom counterpart material is disordered at all temperatures and displays a glass transition temperature T
 g
 ≈−3 °C. Regioregular P3HT is semicrystalline and forms needle or plate like crystallites which in solution cast thin films are oriented with respect to the substrate. Films produced by spin coating display a non-equilibrium structure with reduced order and orientation. Annealing of these films in the liquid crystalline state leads to the formation of a morphology similar to the one observed in solution cast films.

Semicrystalline morphology in thin films of poly(3-hexylthiophene)

We report on structural investigations of a series of regioregular poly(3-hexylthiophene) with well-defined molecular weight (5−19 kg/mol) using DSC, small angle and wide-angle X-ray scattering, and AFM. With increasing temperature, we identify three ordered phases, namely 3D crystalline, 2D crystalline with disordered side chains, and a layered phase of smectic symmetry, followed by complete melting. Although all samples crystallize in extended chain conformation, the lower molecular weight material exhibits a lower crystallinity, most likely caused by noncrystallizable end groups. The crystallinity increases strongly with increasing molecular weight, which could be a possible explanation for the known dependence of charge transport properties on molecular weight.

Temperature and Molecular Weight Dependent Hierarchical Equilibrium Structures in Semiconducting Poly(3-hexylthiophene)

Thermochromism of a series of cast films of poly(3-alkylthiophenes) (P3ATs, A = hexyl, octyl, dodecyl, and hexadecyl) with different head-to-tail (HT) diad content (70−100%) was studied. The thermochromic behavior is found to be controlled by the HT diad content and the side chain length. P3ATs with moderate HT diad content give rise to a clear thermochromic isosbestic point irrespective of the length of the alkyl side chain. Regioregular polymers possessing a >90% HT diad content exhibit either a continuous thermochromic blue shift or an isosbestic point, depending on the alkyl side chain length. The different thermochromic characteristics are attributed to subtle morphological differences between the polymers. DSC and X-ray diffraction studies indicate that P3AT samples with moderate HT regularity are formally amorphous with a quasi-ordered phase dispersed in continuous disordered domains. P3ATs with high HT regularity consist of crystalline, quasi-ordered, and disordered phases. For polymers with short...

M.J. Winokur

Papers

Structural and absorption studies of the thermochromic transition in poly(3-hexylthiophene)