H-Aggregated Form II Spherulite of Poly(3-butylthiophene) Grown from Solution.

New large-size poly(3-butylthiophene) (P3BT) spherulites are obtained by solution aging. These P3BT spherulites are composed of nanoribbons, and the P3BT molecules arrange into Form II structure with a backbone π-stacking distance of 0.47 nm. P3BT lamellae adopt "flat-on" orientation at the edge of the spherulite, and the spherulite preferentially grows along the π-π stacking direction. These spherulites could be obtained in bulk solution or at the top or bottom of the solution, depending on the competition of gravity and Brownian motion. Temperature-dependent photoluminescence spectra demonstrate that the polymer chains are arranged in H-aggregation model. The 0-0 transition in UV-visible absorption spectra blue shifts from 2.03 eV (610 nm, Form I) to 2.11 eV (589 nm, Form II). These results provide a further understanding of the crystallization and photophysical properties of poly(3-alkylthiophene) (P3AT), and the preparation method of large size and pure P3AT spherulites shows potential in applications of organic electronics.