Potential energy surface mapping of ethoxy-dibenzalacetone and fullerene-based quenchers for optoelectronics

Abstract

The photophysical properties of chromophores are influenced by their environment, which modulates both adiabatic and non-adiabatic energy dissipation mechanisms. This thesis explores the role of chemical reactivity descriptors and the potential energy surface (PES) in the fluorescence suppression 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). The quenching mechanism proceeds through static non-fluorescent complexes, as evidenced by the linearity of the Stern-Volmer curves and the unchanged excited-state lifetime (0.20 ns) with increasing quencher concentration. Förster resonance energy transfer (FRET) dominated in PC61BM@DBAd due to its larger spectral overlap integral, leading to a Förster energy transfer rate constant (𝑘FRET) of 3.44 × 1012 s−1, while photoinduced charge transfer prevailed in C60@DBAd, thermodynamically driven by a charge-transfer driving force of −1.84 eV arising from HOMO-LUMO orbital alignment that favored charge transfer exciton (CTE) dissociation with binding energy estimated at approximately 2.29 ± 0.11 eV, as calculated by TD-DFT/PCM at the M06-2X/6-311+G(d,p) level of theory. PES analyses confirm the static ground-state complexes, with pronounced van der Waals interactions in PC61BM@DBAd occurring at a short-range centroid-to-centroid distance of 4.92 Å. Thermodynamic calculations, performed at the DFT/BLYP-D2/DNP+ formalism, confirmed the spontaneity of complex formation, with Gibbs free energy values of −42.53 kcal · mol−1 for C60@DBAd and −51.91 kcal · mol−1 for PC61BM@DBAd. These findings reveal that DBAd effectively transfers the excitation energy and photoinduced charge to the fullerene acceptors by ultrafast non-radiative pathways at 5.0 × 109 s−1, emphasizing C60@DBAd and PC61BM@DBAd self-assemblies as alternative supramolecular complexes for optoelectronic applications, such as organic/fullerene-based devices for next-generation solar cells.