Molecular Arrangement in Cyanine Dye J‑Aggregates Formed on CeO₂ Nanoparticles

The aggregation behavior of 1-methyl-1′-octadecyl-2,2′-cyanine perchlorate (amphi-PIC) and 3,3′-dimethyl-9-(2-thienyl)-thiacarbocyanine iodide (L-21) dyes in binary dimethylformamide (dimethylsulfoxide)/water (1:9) solution containing CeO2 nanoparticles (NPs) has been studied by optical absorption and fluorescent spectroscopy, as well as dynamic light-scattering method. Formation of stable hybrid complexes between NPs and dye J-aggregates due to Coulombic and stacking interactions has been revealed. The arrangement of dye molecules in aggregates (slipping angle θ, twisting angle α, the center-to-center distance R, and the exciton splitting energy ΔE) was analyzed within the Kasha exciton model based on oblique transition dipoles orientation. For amphi-PIC, formation of twisted face-to-face and oblique head-to-tail J-aggregates has been revealed depending on CeO2 NPs concentration, whereas L-21 dye forms aggregates of a twisted face-to-face fashion independently on NPs concentration