The aggregated and crystalline phases of π-conjugated molecules and polymers continue to receive widespread attention as semiconducting materials for field effect transistors, light emitting diodes and solar cells. However, despite the more than five decades of intensive experimental and theoretical research following Kasha's pioneering work on H- and J-aggregates there remain important questions regarding the nature of the photo-excitations in molecular assemblies and how their spectral signatures are related to crystal packing and morphology.  In this talk we show how vibronic signatures are often superior to signatures based on spectral shifts in identifying J- and H-aggregates. We discuss the absorption ratio formula as a means for evaluating the exciton bandwidth and the PL ratio formula as a means for evaluating the exciton coherence length. We further show how the theory of Kasha can be extended to account for intermolecular charge transfer.Applications are made to aggregated rylenes which have been intensively investigated as dye pigments and electron-transporting materials.

Expanded theory of H- and J- molecular aggregates

256th National Meeting (2018)

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