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

Abstract

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.

Photo- and electroluminescence in a series of PPV type terpolymers containing fluorene, thiophene and phenylene units

“…In addition, all of these spectra have a higher intensity red-edge bands which are characteristic of aggregates. Aggregate emission of polymers in solid state is a common phenomenon [18][19][20]26,27]. The LaPPS30-0 emission band is very similar in energy and vibronic structure as other polyfluorenes in [13,20] and some aggregation is evidenced by the red-edge tail around 550 nm.…”

“…When in solid state, in addition to the intrachain energy transfer and charge transfer processes, interchain photophysical processes also play important roles due the possibility of polymer aggregation, a very common process in both polyfluorenes and polythiophenes [18][19][20][21][22][23][24][25][26][27]. In photoluminescence (PL), along with the emission of isolated chains, emission of aggregates may be possible in some cases, whereas in others the quenching of the emission is the most important process.…”

Molecular relaxations in polyfluorene based cast films

“…An interesting feature is that the curves for carbons in the middle and end of the side-chain are similar in Ge108 (so the side-chain execute large angle rotations), but clearly distinct in Be329. This difference is explained taking into account that BE329 has a crystalline phases where the side chains are heavily packed [13], leading to fraction of side-chains that only can execute restricted rotations [13]. Thus, one can ascribe these side chain motions to the ␤ relaxation that appears at low temperatures in the DMTA data.…”

“…Solid-State NMR experiments were performed using a 9.4 T VARIAN spectrometer in a 7-mm MAS-VT probe head. Typical /2 pulses lengths of 3.5 and 4.0 s were applied for 13 C and 1 H.…”

Side-Chain Influence on the Mass Density and Refractive Index of Polyfluorenes and Star-Shaped Oligofluorene Truxenes

“…Methods reported in the literature to study the density of thin films include the pressure-of-flotation method 23 , Xray reflectivity 24 , selected-area electron diffraction combined with X-ray diffraction 25 , and the solution absorbance method 26 . In the pressure-of-flotation method the density is obtained by measuring the relative density difference and mass difference between a clean substrate and a substrate coated with the film.…”