External control of chemical processes is a subject of widespread interest in chemical research, including control of electrocatalytic processes with significant promise in energy research. The electrochemical double-layer is the...
Molecular
orientation at the donor–acceptor interface plays
a crucial role in determining the efficiency of organic semiconductor
materials. We have used vibrational sum frequency generation spectroscopy
to determine the orientation of poly-3-hexylthiophene (P3HT) at the
planar buried interface with fullerene (C60). The thiophene
rings of P3HT have been found to tilt significantly toward C60, making an average angle θ ≈ 49° ± 10°
between the plane of the ring and the interface. Such tilt may be
attributed to π–π stacking interactions between
P3HT and C60 and may facilitate efficient charge transfer
between donor and acceptor. Upon annealing, the thiophene rings tilt
away from the interface by Δθ = 12–19°. This
may be attributed to higher crystallinity of annealed P3HT that propagates
all the way to the interface, resulting in more “edge-on”
orientation, which is consistent with the observed red-shift by ∼6
cm–1 and spectral narrowing of the C=C stretch bands.
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