Unraveling the Contribution of Residual Monomer to
the Emission Spectra of Poly(3-hexylthiophene) Aggregates: Implications
for Identifying H- and J‑type Coupling
posted on 2021-06-22, 16:34authored byStephanie
N. Kramer, Jasper Brown, Megan Rice, Linda A. Peteanu
Poly(3-hexylthiophene)
(P3HT) is a well-studied benchmark system
for semiconducting polymers used in optoelectronic devices. In these
materials, aggregation can improve charge transport efficiency or
enhance emission yields depending on the interchain packing. This
may be inferred from the absorption and emission spectra when analyzed
using exciton coupling models such as the well-known H- and J-coupling
model of Kasha. The more recently developed weakly coupled H-aggregate
(WCH) model quantifies the degree of disorder via the ratio of the
electronic origin intensity to that of the first vibronic band. Here,
the underlying assumptions of this approach are tested experimentally
for P3HT aggregates formed by solvent poisoning using bulk and single-molecule-based
spectroscopic techniques. Specifically, we show that the contribution
of residual monomeric chains to the aggregate spectrum must be accounted
for to properly assign the spectra as H- or J-type. A modification
of the WCH model is introduced to account for multiple emissive species.