The studied stabilizers K,Na-PHI, KMel, KCya, and KCA are water-soluble ionic compounds bearing negatively charged functional groups (see Fig. ). In particular, K,Na-PHI consists of a poly(heptazine imide) network incorporating, apart from NH and -NH2 groups or uncondensed NHx-including triazine species, also terminal cyanamide N-C≡N -and cyamelurate C-O -functional groups. We have reported that the dissolved K,Na-PHI has a zeta potential of -31 mV at a pH of 7.5, confirming the negatively charged surface under our reaction conditions. The presence of the negatively charged functional groups on the stabilizers allows for electrostatic stabilization and solubilization of Au NPs in water.