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

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 (C60 and PC61BM). 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) × 104 and (2.27 ± 0.10) × 104 L·mol–1 for C60@DBAd and PC61BM@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 PC61BM@DBAd, consistent with the larger spectral-overlap integral, whereas photoinduced charge transfer (CT) is comparatively more competitive in C60@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 PC61BM@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 C60@DBAd and PC61BM@DBAd complexes as potentially relevant for organic-fullerene solar cells.