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.