Exploring photophysical behavior and fullerene-induced quenching in Difluoroboron Flavanone β-Diketonates for application in organic electronic devices: Experimental and Theoretical Analysis

The photophysical properties of two difluoroboron flavanone β-diketonates (DK1 and DK2) and their interaction with fullerene (C₆₀) in toluene solution and spin-coated films were investigated using time-correlated single-photon counting, absorption spectroscopy, and steady-state fluorescence spectroscopy. In molecular crystal, the complexes exhibited red-shifted absorption and emission relative to their spectra in solution. Additionally, both complexes displayed bi-exponential decay behavior in time-resolved fluorescence measurements, indicating their capability to form both H and J types of aggregates in the solid state. The introduction of C₆₀ resulted in significant fluorescence quenching and reduced excited-state lifetimes for both complexes. This quenching, observed in both solution and spin-coated films, was primarily driven by photo-induced electron transfer (PET) processes, underscoring the potential of these complexes as donors in fullerene-based heterojunction organic solar cells. To elucidate the process of aggregate formation and the impacts of different dimerization types within the crystalline structure of the complexes, first-principles calculations using Density Functional Theory (DFT) and time-dependent density functional theory (TD-DFT) were performed. We also employed DFT to explore various DK configurations on the fullerene surface, evaluating intermolecular distances and formation energies. These calculations highlighted the energetically favorable gap between the low-lying LUMO levels of the complexes and C₆₀, confirming their suitability for such applications.