Irreversible Chemical Collapse in Perylene-Based PAH Nanofluids: Toward the Terminal State ϕ^∞

We present a comprehensive experimental investigation into the chemical saturation behavior of perylene-based polycyclic aromatic hydrocarbons (PAHs) in nanofluid environments. Through stepwise electrophilic halogenation and oxidative functionalization, we identify a critical substitution threshold beyond which the conjugated π-electron system undergoes irreversible collapse. This transition is characterized by a complete loss of UV–Vis absorption, disappearance of Raman-active aromatic bands, and a sharp decline in colloidal stability ($\zeta$-potential $\rightarrow$ 0 mV). We define this chemically inert, non-dispersible state as the terminal saturation point of the PAH framework. The study integrates quantitative spectroscopy, elemental analysis, and dispersion behavior, offering clear mechanistic insight into structure–function breakdown at high functionalization densities. These findings have direct implications for PAH-based nanomaterials, providing experimentally grounded limits for functionalization strategies and nanofluid design.