## 2 Results and Discussion
### Interactions and Dispersion Stability of Anion-\(\pi\) Type PNPs with R-254 and Y-180  
For organic pigments with intermolecular forces of H-bonds, it was assumed that the anions of these PNPs acted as H-bond acceptors and formed salt-bridge H-bonds with the pigments. The formation of salt-bridge H-bonds enhanced the dispersion stability of pigments in water. The strength of the H-bond acceptors is related to the basicity strength and the number of anions [43; 44]. Constrained by the solvent resistance of these PNPs, the number of anions failed to be measured using methods such as gel permeation chromatography (GPC) and elemental analysis (EA). However, an assessment can be made by referring to the \(\zeta\) values of these PNPs in water (Figure 1d). This is because the \(\zeta\) values are indicative of the surface charge and stability of the particles, which can be influenced by the number of anions present. Therefore, the H-bond acceptors exhibited the following order of strength: PNPs-5 > PNPs-4 > PNPs-3 > PNPs-2 > PNPs-1. The interactions between these PNPs and pigment R-254 were investigated using ATR-FTIR and XPS spectra. The experimental results verified the formation of salt-bridge H-bonds between some of these PNPs and R-254. Stronger H-bonds result in higher frequencies of peaks in the FTIR spectra [45], and the detailed characterization of the formation of salt-bridge H-bonds has been reported by [PERSON] et al. [46; 47]. The results of ATR-FTIR spectra showed that new peaks were observed at 3628 cm\({}^{-1}\) after R-254 was mixed with PNPs-4 or PNPs-5. The new peaks strongly suggested the formation of salt-bridge H-bonds ([N-H\(\cdots\)O]\({}^{-}\)) between these two PNPs and R-254. In the mixtures, the O-H peaks shifted to higher frequencies, namely 3406 and 3450 cm\({}^{-1}\) (Figure 4a), respectively. Moreover, no peak was observed at 3628 cm\({}^{-1}\) for PNPs themselves (Figure S14). While no salt-bridge H-bonds were formed in the mixtures of R-254 with PNPs-1, PNPs-2, or PNPs-3, the N-H peaks of all these mixtures shifted to higher frequencies (Figure 4b, Table S5). This indicated that the classical H-bonds (N-H\(\cdots\)O) were formed between these three PNPs and R-254 [48]. In the mixtures of R-254 with PNPs-1, PNPs-2, or PNPs-5, the C=O peaks also shifted to higher frequencies (Figure 4c). This further indicated that the formation of these H-bonds led to the dissociation of N-H\(\cdots\)O=C among R-254 molecules, resulting in a subsequent weakening of the ordered H-bonds. Furthermore, the high-resolution XPS spectra of N 1s for R-254 can be deconvoluted into two peaks, including the N-C peak at 399.94 eV and N-H peak at 399.60 eV. After mixing with these PNPs, all the N-H peaks shifted to higher binding energies (Figure 4d). In the mixtures of R-254 with PNPs-4 or PNPs-5, new peaks at 398.67 eV were observed, which were attributed to [N-H\(\cdots\)O]\({}^{-}\). The proportions of the [N-H\(\cdots\)O]\({}^{-}\) peak area were calculated to be 7.32% and 9.23% for the two mixtures, respectively. This result indicated that a higher number of salt-bridge H-bonds had been formed between PNPs-5 and R-254 (Figure S15). In addition, the proportion of the N-H peak area in R-254 was initially 58.47%. After mixing with these PNPs, it gradually decreased (Figure 4e). This phenomenon clearly indicated that the degree of dissociation of the ordered H-bonds among R-254 molecules was gradually increasing. All the peak parameters are listed in Table S6 of the Supporting Information. The results of ATR-FTIR and XPS spectra jointly verified the order of the interactions' strength between these PNPs and R-254 as follows:R-254 + PNPs-5 > R-254 + PNPs-4 > R-254 + PNPs-3 > R-254 + PNPs-2 > R-254 + PNPs-1. This order was consistent with that of H-bond acceptor strength, strongly suggesting that stronger H-bond acceptors facilitated the formation of salt-bridge H-bonds. Subsequently, the dispersion stability of the mixtures of these PNPs with R-254 in water was investigated.