Raman spectroscopy on neat and doped conjugated polymers

Licentiatavhandling, 2026

Conjugated polymers are a class of materials that combine the mechanical
flexibility and processability of conventional polymers with tunable electronic
properties. The backbone of conjugated polymers consists of alternating single
and double bonds, creating a delocalized 𝜋-electron system that enables charge
transport. While these materials are intrinsically semiconducting, their electrical
conductivity can be significantly enhanced through chemical or electrochemical
doping, making them suitable for a wide range of semiconducting applications.
In addition to their electronic functionality, conjugated polymers retain the
advantageous mechanical properties of soft materials, such as flexibility and low
weight. Importantly, both the mechanical and electronic properties are highly
dependent on the chemical structure, including the backbone design and the
nature of the side chains, which influence molecular packing, intermolecular
interactions, and overall material morphology.

In this work, Raman spectroscopy is employed as the primary analytical tech-
nique to investigate the structural, electronic, and vibrational properties of a
thienothiophene-based conjugated polymer functionalized with polar triethylene
glycol side chains. Raman spectroscopy is particularly well suited for studying
conjugated systems due to its sensitivity to molecular vibrations associated with
the 𝜋-conjugated backbone, enabling detailed insights into bonding, conjugation
length, and doping-induced structural changes. An experimental methodology
for the assignment of vibrational modes is presented, combining spectral ana-
lysis with systematic variations in experimental conditions to accurately identify
characteristic vibrational signatures.

Temperature-dependent Raman measurements are further employed to probe
the thermal behavior of the polymer, providing insight into dynamic processes
such as molecular relaxation and the glass transition. In addition, the potential of
spatially resolved Raman mapping is explored as a powerful tool for investigating
heterogeneities within the material, particularly in relation to localized doping
phenomena.