Epitaxially grown highly oriented
crystalline films, named form
I and form II, and spin-coated films of poly{[<i>N</i>,<i>N</i>′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-<i>alt</i>-5,5′-(2,2′-bithiophene)}, P(NDI2OD-T2),
have been investigated through infrared vibrational spectroscopy techniques
(infrared absorption in double transmission at normal incidence (IRA-TR)
and reflection absorption infrared spectroscopy at grazing angle incidence
(RAIRS)) to get access to polymer chain orientation and structure.
An analytic model to correlate the experimental intensities of the
IR bands with structural parameters has been developed and applied
for the three film morphologies. While spin-coated and form I films
show P(NDI2OD-T2) chains lying parallel to the substrate in the face-on
arrangement, form II films feature a structure with chains tilted
out from the surface. The combined experimental and theoretical methodology
gives insights into the local molecular orientations of naphthalene
diimide (NDI2OD) and bithiophene (T2) counits. This approach can be
easily extended to a variety of organic polymer semiconductors, allowing
one to directly correlate molecular structure to properties such as
charge transport, which is of fundamental relevance for developing
quantitative models for applications in organic electronics and photovoltaics
