Side-chain influence on the mass density and refractive index of polyfluorenes and star-shaped oligofluorene truxenes

Morawska, Paulina O. and Wang, Yue and Ruseckas, Arvydas and Orofino-Penia, Clara and Kanibolotsky, Alexander L. and Santhanagopal, Ramkumar and Fröhlich, Nils and Fritsch, Martin and Allard, Sybille and Scherf, Ullrich and Skabara, Peter J. and Samuel, Ifor D W and Turnbull, Graham A. (2015) Side-chain influence on the mass density and refractive index of polyfluorenes and star-shaped oligofluorene truxenes. Journal of Physical Chemistry C, 119 (38). pp. 22102-22107. ISSN 1932-7447 (https://doi.org/10.1021/acs.jpcc.5b05526)

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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 star-shaped 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<sup>3</sup> 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<sup>3</sup>, which also decreased with increasing side-chain length.

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