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.

We present the synthesis, characterization, and structural analysis of a thiophene-rich heteroacene, dibenzothiopheno[6,5-b:6',5'-f]thieno[3,2-b]thiophene (DBTTT) as well as its application in field-effect transistors. The design of DBTTT is based on the enhancement of intermolecular charge transfer through strong S-S interactions. Crystal structure analysis showed that the intermolecular π-π distance is shortened and that the packing density is higher than those of the electronically equivalent benzene analogue, dinaphtho-[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT). The highest hole mobility we obtained in polycrystalline DBTTT thin-film transistors was 19.3 cm(2)·V(-1)·s(-1), six times higher than that of DNTT-based transistors. The observed isotropic angular mobilities and thermal stabilities at temperatures up to 140 °C indicate the great potential of DBTTT for attaining device uniformity and processability.

Four kinds of new π-conjugated copolymers of electron-donating thiophene with highly electron-withdrawing pyrido[3,4-b]pyrazine derivatives have been prepared by using the Stille reaction and electrochemical oxidative polymerization in high yields, and their optical and electrochemical properties have been compared with those of previously reported CT-type π-conjugated polymers. Chemically prepared polymers show an [η] value of about 0.3 dL g-1. The π−π* absorption bands (λmax = ca. 633 nm) of the copolymers are observed at a longer wavelength by about 30 nm than those of similar CT-type copolymers of thiophene with pyridine and quinoxaline. These UV−vis data are considered to reflect a stronger CT interaction between thiophene and pyrido[3,4-b]pyrazine, which has a higher electron-withdrawing ability than pyridine and quinoxaline. The copolymers are electrochemically active in both oxidation and reduction regions. In the reduction (n-doping) region, the copolymers show normal three couples of n-doping and n-undoping between −1.55 and −2.25 V vs Ag/Ag+. On the other hand, they receive oxidation (p-doping) at E pa of 0.9 V vs Ag/Ag+. The electrochemical p- and n-doping of the film of the copolymers is accompanied by changes in its UV−vis spectra (electrochromism), and new absorption bands emerge in the range 900−1500 nm by the p- and n-doping. The X-ray diffraction pattern of the copolymer having a long alkyl side chain suggests self-assembling of the polymer assisted by side chain crystallization.

Five kinds of polythiophenes bearing a crown ethereal subunit directly bonded to the thiophene ring have been prepared by the following organometallic polycondensation:,5-diyl with the crown ethereal subunit. Polythiophenes with alkoxy substituents (OCH3 and O(CH2)2OCH3) are also prepared by the organometallic polycondensation. The crown ethereal polymers exhibit photoluminescence in a range of 467-603 nm in both CHCl3 solutions and films. Their electroluminescence spectra essentially agree with the photoluminescence spectra. The crown ethereal polythiophenes have a high affinity toward Na + . After chemical oxidation (or p-doping) and reduction (or n-doping), the polymers show an electrical conductivity of 5.4 × 10 -7 to 1.8 S cm -1 . The Na-doped and electrically conducting state of crown ethereal polythiophenes shows some stability under air, which is attributed to the strong affinity of the polymer to Na + . Cyclic voltammetry of the crown and linear ethereal polythiophenes reveals a large difference (about 2 V) between n-doping and n-undoping potentials.