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.

Classical genetic analysis has revealed that the determinate habit of soybean (Glycine max) is controlled by a recessive allele at the determinate stem (Dt1) locus. To dissect the molecular basis of the determinate habit, we isolated two orthologs of pea (Pisum sativum) TERMINAL FLOWER1a, GmTFL1a and GmTFL1b, from the soybean genome. Mapping analysis indicated that GmTFL1b is a candidate for Dt1. Despite their high amino acid identity, the two genes had different transcriptional profiles. GmTFL1b was expressed in the root and shoot apical meristems (SAMs), whereas GmTFL1a was mainly expressed in immature seed. The GmTFL1b transcript accumulated in the SAMs during early vegetative growth in both the determinate and indeterminate lines but thereafter was abruptly lost in the determinate line. Introduction of the genomic region of GmTFL1b from the indeterminate line complemented the stem growth habit in the determinate line: more nodes were produced, and flowering in the terminal raceme was delayed. The identity between Dt1 and GmTFL1b was also confirmed with a virus-induced gene silencing experiment. Taken together, our data suggest that Dt1 encodes the GmTFL1b protein and that the stem growth habit is determined by the variation of this gene. The dt1 allele may condition the determinate habit via the earlier loss in GmTFL1b expression concomitant with floral induction, although it functions normally under the noninductive phase of flowering. An association test of DNA polymorphisms with the stem growth habit among 16 cultivars suggested that a single amino acid substitution in exon 4 determines the fate of the SAM after floral induction.