Establishing a Correlation between Charge Transfer Properties in Organic Semiconductors and the Excitonic Parameters Extracted by Electroabsorption Spectroscopy

The excitonic behavior of Coulomb-bound electron-hole pairs in organic molecules plays a pivotal role in determining the performance of organic electronic devices. Understanding the correlation between molecular structure and excitonic properties can facilitate more efficient material design to achieve better device performance. However, experimental techniques that can qualitatively assess these excitonic properties are currently limited, and previous studies are mainly based on theoretical calculations which have limitations on resolving systems with interactions of multiple molecules. More importantly, calculations are based on existing established theories or models, which might not be able to explore any new properties of materials. Experimentally, electroabsorption (EA) spectroscopy stands out as a promising method, allowing for the extraction of changes in dipole moment (Δμ) and polarizability (Δp) between the ground and excited states. These parameters are closely linked to the exciton recombination and dissociation processes. Despite its potential, a systematic application of EA across different materials is still lacking, leading to inconsistencies in how Δμ and Δp are interpreted in relation to excitonic properties. Moreover, conventional interpretations often rely on an overly simplified hydrogen-like model, where an electron orbits a stationary hole, overlooking the more complex delocalization of electron and hole scenarios in organic materials.This research proposal aims to address these challenges by investigating the discrepancies in the interpretation of excitonic properties based on EA-derived Δμ and Δp values. EA spectroscopy will be conducted on a series of materials that vary in molecular structure, molecular packing, and interactions with other materials. To ensure accurate correlations, the EA results will be cross-referenced with theoretical calculations and independent transient absorption spectroscopy data. The gained insight will be further applied to investigate the contribution from different molecular packing configurations on the charge transfer, and the charge transfer properties at organic donor/acceptor bulk heterojunctions.The success of this project will significantly enhance the qualitative understanding of excitonic properties in organic electronic materials, offering valuable insights that inform molecular design for improved charge transfer processes. Specifically, the findings will help address current limitations by enabling more accurate evaluations of charge transfer properties at organic interfaces. Furthermore, the development of a quantitative relationship between excitonic properties and molecular structure will support more efficient, AI-driven material development, reducing reliance on empirically driven, holistic approaches traditionally employed only by experienced chemists.