Fluorescence Quenching Driven by PES-Guided Self-Assembly of Ethoxy-Dibenzalacetone and Fullerene-Based Quenchers: A Theoretical and Experimental Study

High Resolution Image Download MS PowerPoint Slide Photophysical properties of π-conjugated chromophores are strongly influenced by their molecular environment, which modulates the adiabatic and nonadiabatic energy dissipation. This theoretical and experimental study investigates the chemical reactivity descriptors and potential energy surfaces (PES) underlying the fluorescence quenching of the ethoxy-dibenzalacetone derivative (DBAd) [(1E,4E)-1,5-bis(4-ethoxyphenyl)penta-1,4-dien-3-one] by fullerene-based quenchers (C 60 and PC 61 BM). Quenching proceeds via the formation of predominantly static and nonfluorescent complexes, supported by linear Stern–Volmer behavior yielding association constants of (1.83 ± 0.05) × 10 4 and (2.27 ± 0.10) × 10 4 L·mol –1 for C 60 @DBAd and PC 61 BM@DBAd, respectively, and by an unchanged DBAd excited-state lifetime (∼0.20 ns) across quencher concentrations. Förster resonance energy transfer (FRET) contributes more prominently to quenching in PC 61 BM@DBAd, consistent with the larger spectral-overlap integral, whereas photoinduced charge transfer (CT) is comparatively more competitive in C 60 @DBAd, thermodynamically favored by the HOMO–LUMO alignment at the donor–acceptor interface. PES analyses qualitatively support stable ground-state complexes with stronger short-range stabilization for PC 61 BM@DBAd at intermolecular distances of ∼4.9 Å. Overall, DBAd channels excitation to fullerene acceptors through competing nonradiative energy- and charge-transfer pathways, revealing that fluorescence quenching is driven by PES-guided ground-state noncovalent self-assembly and highlighting C 60 @DBAd and PC 61 BM@DBAd complexes as potentially relevant for organic-fullerene solar cells.