We then studied the photophysical properties of these two molecules in water. Generally, the photophysical properties are usually associated with molecular structures and self-assembly behavior. As shown in Figure exhibits the main UV absorption peak at 315 nm, whereas M2-I shifts towards the longer wavelength at 353 nm. The fluorescence emission peak of M1-I is located at 476 nm, and M2-I exhibits a redshift at 500 nm. This is understandable since the introduction of the vinyl linkage extends the π-conjugation and thus leads to the redshift in the UV absorption and fluorescence spectra. Similar absorption and emission properties were observed when the counter anion was exchanged to chloride (Figure and). Notably, M1-X (X = I -or Cl -) exhibits more than ten times stronger fluorescent intensity than M2-X (X = I -or Cl -) (Figure and). M1-X (X = I -or Cl -) is composed of rigid bonds between the benzene rings, which effectively increase the conformational rigidity and reduce the loss of energy via vibration motions, thus will produce strong fluorescence. 62 M2-X (X = I -or Cl -) with flexible vinyl bridges makes the structure lack rigidity and thus produce weak fluorescence. In the meanwhile, the two precursors, M1-X (X = I -or Cl -) and M2-X (X = I -or Cl -), with counter anions chloride, show stronger emitting fluorescence and less brightness than counter anions iodide under 365 nm light irradiation (Figure , S3d, S3e and S3f). This is due to the fluorescence quenching and chromogenic effects of iodide ions. To gain further insights into the self-assembly process, single crystals of M1-I, M1-Cl and M2-I were acquired through a carefully controlled, gradual cooling process of recrystallization. For the details, see the Supplementary Materials. As shown in Figure As shown in Figure , M1-I was deliberately crafted with a central hexaphenylbenzene core and six protruding methylpyridine arms. These six arms were meticulously aligned in a head-to-tail manner, resulting in a captivating triangular plane tiling arrangement. The distance between the two neighboring methylpyridine planes is 3.61 Å. A clearly 2D layered structure was observed from the a or baxis direction, which adopted an eclipsed (AA) stacking mode (Figure and). A clear channel structure formed, which can be seen from the c-axis direction. The distance between each layer is 8.40 Å. The counter anions I -exist inside the triangle pores and between the layers (Figure and 2h). For M1-Cl, the self-assembly mode in each layer is exactly the same as M1-I. The distance between the two neighboring methylpyridine planes is 3.36 Å (Figure ). However, the stacking mode of M1-Cl is completely different. An obvious staggered shift was observed. A regular ABC stacking mode is adopted, and the distance between the layers is 8.60 Å (Figure , 2e and 2f). The counter anions Cl -exist inside the triangle pores in each layer and intervals between the layers (Figure and). The types of counter anions affect the self-assembly modes along the c-axis due to the changes in the hydrogen bond formation between the counter anions and the hydrogen in the monomers. While the self-assembly modes are the same in the 2D plane of a or b-axis directions due to the stronger hydrophilic and hydrophobic interactions.