## 2 Results and Discussion  
### Synthesis and Characterization of Antion-\(\pi\) Type PNPs  
A series of anion-\(\pi\) type PNPs were synthesized using a simple emulsion polymerization method, which significantly improved the dispersion stability of organic pigments in water. In an oil-in-water emulsion system, the oil phase contained hydrophobic monomers (styrene (St) and divinylbenzene (DVB)), while the aqueous phase included an initiator (potassium persulfate (KPS)) and anionic hydrophilic monomers (Figure 1a, Table S1). Five hydrophilic monomers with different anionic structures were utilized for the preparation of PNPs: sodium vinyl phosphate (SVPA), sodium allylsulfonate (SAS), sodium acrylate (SAA), sodium 4-vinylbenzoic acid (SVBZ), and sodium 4-styrenesulfonate (SS). Scanning electron microscope (SEM) images showed that all of the synthesized PNPs exhibited a spherical structure with an average particle size less than 60 nm. (Figures 1b and S1). The functional groups of these PNPs were analyzed using Fourier transform infrared (FTIR) spectra (Figure S1). These PNPs showed absorption peaks at 1600, 1493, and 1450 cm\({}^{-1}\), which can be assigned to the skeletal vibration of the benzene ring [24]. Particularly, for PNPs-1, the peak at 1150 cm\({}^{-1}\) can be attributed to P=O stretching vibration, while another peak at 973 cm\({}^{-1}\) corresponds to the asymmetric stretching vibration of P-O [25]. For PNPs-2 and PNPs-5, the peaks at 1180 and 1040 cm\({}^{-1}\) can be attributed to the stretching vibrations of S=O and S-O, respectively [26]. For PNPs-3 and PNPs-4, the peaks in the range of 1680-1730 cm\({}^{-1}\) can be attributed to C=O stretching vibration, and the peak at 1541 cm\({}^{-1}\) belongs to C-O vibration [27]. In addition, the wide scan survey X-ray photoelectron spectroscopy (XPS) spectra demonstrated the existence of the elements C, O, and P in PNPs-1. The elemental compositions of PNPs-2 and PNPs-5 consisted of C, O, and S, while the signals of C and O were observed in PNPs-3 and PNPs-4, respectively (Figure S3). The results from both FTIR and XPS indicated that PNPs with different anionic structures were successfully synthesized. Subsequently, the contact angles and zeta potential (\(\lambda\)) values were measured to investigate the hydrophilicity of these PNPs [28]. As shown in Figure 1c, these PNPs were hydrophilic with contact angles less than 90\({}^{\circ}\). PNPs-5 exhibited the smallest contact angle (CA = 21.2 \(\pm\) 0.3\({}^{\circ}\)) (Figure S4). The \(\zeta\) values indicate the charge properties and dispersion stability of particles, and a higher absolute \(\zeta\) value suggests a more stable dispersion system for the particles [29]. The results showed that the \(\zeta\) values of these PNPs were \(-\)38.3 \(\pm\) 1.1, \(-\)40.9 \(\pm\) 0.7, \(-\)45.9 \(\pm\) 0.2, \(-\)64.4 \(\pm\) 1.4, and \(-\)74.2 \(\pm\) 0.9 mV, respectively (Figure 1d). This indicated that these PNPs possessed excellent water dispersion stability. In addition, these PNPs exhibited highly stable negative charge properties across the pH range of 0 to 14 (taking PNPs-5 as an example, Figure 1e), indicating that these PNPs also possessed excellent dispersion stability in acidic and alkaline conditions. The solvent resistance was demonstrated by dispersing these PNPs in various organic solvents, including dimethyl sulfoxide (DMSO), ethylene glycol (EG), methanol (MeOH), acetonitrile (ACN), acetone, ethanol (EtOH), dichloromethane (DCM), toluene, and petroleum ether (PE), ranging from high polarity to low polarity. After 24 h of dispersion, all PNPs demonstrated no dissolution or swelling in these solvents (Figures 1f and S5). Notably, these PNPs dispersed evenly in high-polarity solvents. Particularly, they exhibited excellent dispersion in EG, which is commonly utilized as a wetting agent for water-based inkjet inks [30]. Subsequently, the viscosities of these PNPs dispersed in water were tested with their contents ranging from 5 to 50%.