Molecular Packing in Crystalline Poly(9,9-di-n-octyl-2,7-fluorene)

• Published in: Macromolecules 2004-09, Vol.37 (18), p.6833-6838
• Main Authors: Chen, S. H, Chou, H. L, Su, A. C, Chen, S. A
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Structure, morphology and analysis
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma049346a

Presented are transmission electron microscopic observations of micron-sized single crystals of poly(9,9-di-n-octyl-2,7-fluorene) (PFO) prepared from thin films in the melt state. A preliminary determination of unit cell dimensions and molecular packing (orthorhombic, a = 2.56 nm, b = 2.34 nm, c = 3.32 nm, 8 chains, with space group P212121 and density 1.041 g mL-1) was made via combined considerations of the selected-area electron diffraction (SAED) pattern obtained along the [00l] zone of the single crystals, the SAED “fiber” pattern obtained from shear-oriented films, and the “powder” pattern from X-ray diffraction of melt-crystallized thick films in the absence of preferred orientation. In this model, PFO backbones are generally separated by transversely extended alkyl side chains, consistent with the dominance of single-chromophore emissions and the general lack of interbackbone delocalization of PFO chains in this ordered state as indicated by earlier photophysical studies. In addition, microscopic evidence for the presence of a vast number of nanograins was presented, and its implications in the crystallization process of semirigid PFO chains were discussed.