文摘
Orientation and order of distinct molecular subunits in solid layers of the high mobility n-type copolymer poly[N,N′-bis(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-5,5′-(2,2′-bithiophene) P(NDI2OD-T2) are investigated by means of infrared transition moment orientational analysis. This novel spectroscopic technique based on concurrent absorbance measurements of structure-specific bands in dependence on inclination and polarization of the incoming light enables to determine the complete tensor of absorption independently for each transition moment. As a result, for nanometer thin films pronounced in-plane anisotropy arising from self-aggregated order is detected, which, however, is no longer discernible for micrometer thick samples. In contrast, the out-of-plane orientation (inclination of molecular subunits) is retained irrespective of the widely varying layer thicknesses (150 nm vs 1.4 μm). Thus, the conception of the sample morphology occurs as stratification of slightly misaligned layers of oriented polymers; with increasing film thickness the macroscopic in-plane order diminishes, whereas the out-of-plane orientation is preserved.
