Near-Triangular Imprint in Crystalline Pentacene: A Search for Kasha’s Exciton Trimer in a Noncovalent Chromophoric Assembly

Atypical photophysical behaviors of organic chromophores,
tailored
by exciton interactions, are of immense importance owing to the implications
in fabricating photofunctional materials. Kasha’s exciton theory
offers a comprehensive framework for understanding molecular arrays,
predicting unique exciton splitting in dimer and trimer systems, and
their resulting optoelectronic properties. Herein, we report an investigation
of an unexplored molecular triangle in a crystalline pentacene derivative
shaped by noncovalent interactions as well as an extension to linear
acene trimer models. The energetic alignment of excited states was
portrayed using TD-DFT, which suggests a partially split triple degeneracy
according to the alignment of transition dipoles, in agreement with
the molecular exciton model. The crystalline pentacene triangle exhibits
weak excitonic coupling due to significant interchromophoric separation,
which is reflected in the optical properties. The study of the triangular
architecture offers valuable insights into exciton theory in emerging
photonic materials.