  We exploited the high temporal and spatial resolution of neutron spin echo
spectroscopy to investigate the large-scale dynamics of semiflexible conjugated
polymer chains in solutions. We obtained the first experimental demonstration
of earlier predicted single chain glassy state. We used a generalized approach
of the well-established Zimm model of flexible polymers to describe the
relaxation mode spectra of locally stiff polythiophene chains. The Zimm mode
analysis confirms the existence of beads with a finite length that corresponds
to a reduced number of segmental modes in semiflexible chains. Irrespective of
the temperature and the molecular weight of the conjugated polymer, we witness
a universal behavior of the local chain stiffness and invariability of the
beads length. Our experimental findings indicate possibly minor role of the
change in {\pi}-electron conjugation length (and therefore conjugated backbone
planar to non-planar conformational transition) in the observed thermochromic
behavior of polythiophene but instead point on the major role of chain dynamics
in this phenomenon.
