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

Abstract

The density of organic semiconductor films is an important quantity because it is related to intermolecular spacing which in turn determines the electronic and photophysical properties.We report thin film density and refractive index measurements of polyfluorenes and starshaped oligofluorene truxene molecules. An ellipsometer and a procedure using a spectrophotometer were used to determine film thickness and mass of spin-coated films, respectively. We present a study of the effect of alkyl side chain length on the volumetric mass density and refractive index of the materials studied. The density measured for poly(9,9-di-n-octylfluorene) (PF8) was 0.88 ± 0.04 g/cm 3 and decreased with longer alkyl side chains. For the truxene molecule with butyl side chains (T3 butyl), we measured a density of 0.90 ± 0.04 g/cm 3 , which also decreased with increasing side-chain length.2

Coherent acoustic phonon dynamics in chiral copolymers

“…For normal incidence and ideal mechanical contact, the intensity reflection coefficient R 12 of an acoustic wave at an interface can be determined from the acoustic impedances Z 1 and Z 2 of the two media as R12=true(Z1−Z2Z1+Z2true)2, with Zi=ρi cL,i.Here, ρ i and c L, i are the density and the speed of sound in the two media, respectively. Using typical values for a polymer/nitrogen interface [ ρ nitrogen = 1.138 kg m −3 (ideal gas), c L,nitrogen = 350.8 m s −1 , 31 ρ polymer = 880 kg m −3 (polyfluorene PF8), 32 and c L,polymer = 2550 m s −1 (PFPh)], one obtains the reflectivity R 12 (polymer/nitrogen) = 100%, which is the “zero-stress boundary condition” for a free surface 4 . Therefore, significant attenuation of the sound wave only occurs at the glass/polymer interface, having an “approximately zero displacement boundary condition.” 4 Because the measured damping time constant is close to the measured oscillation period, i.e., τ d ≈ τ a , the “experimentally determined reflectivity” is about 1/ e (= 37%).…”

Theory-Driven Insight into the Crystal Packing of Trialkylsilylethynyl Pentacenes

“…Single crystals of organic semiconductors provide distinctive systems to investigate how molecular structure, including the chemical composition, atomic arrangements, and larger molecular architecture, can be tuned to precisely direct molecular packing. As such, crystal engineering, and in particular the use of solubilizing alkyl side chains to guide the molecular packing of electronically active polycyclic aromatic hydrocarbon (PAH) chromophores, is a highly active field. − …”

Ionic Conductivity in Polyfluorene-Based Diblock Copolymers Comprising Nanodomains of a Polymerized Ionic Liquid and a Solid Polymer Electrolyte Doped with LiTFSI

“…This situation is similar to the PEO-based electrolytes at the respective salt concentrations. − ,− Informative at this point is the comparison of the normalized ionic conductivity by the volume fraction of the EO-rich nanophase of the undoped and the salt-doped diblock copolymer electrolytes with the respective conductivity of the homopolymer PEO/LiTFSI (Figure ). For the undoped electrolytes, the volume fraction of the EO-PF phase is Here, A refers to the EO-PF repeat and B to the IL+PF repeat, PA and PB refer to the respective polymers, υ i = M i /ρ i Ν Α is the volume of the each phase, M i is the molar mass ( M EO = 44.05 g·mol –1 , M fluorene = 166.22 g·mol –1 , and M IL = 304.51 g·mol –1 ), and ρ i is the density of each component (ρ PEO = 1.128 g·cm –3 , ρ PF = 0.88 g·cm –3 , and ρ IL = 1.23 g·cm –3 ). − Subsequently, we calculated the volume fraction of EO in the EO-PF nanophase, by employing eq (in this case, as A refers to the EO phase and as B refers to the PF phase). As a result, the volume fraction of the EO phase is 0.40, 0.45, and 0.50, for the undoped electrolytes with x = 3, 4, and 5 EO repeat units.…”