The synthesis, self‐assembly, and spectroscopic investigations of spiropyran (SP)‐functionalized dendron 1 are reported. Under UV light irradiation, assembly of 1 into nano‐/microparticles occurs due to the transformation of the closed form of SP into the open merocyanine (MC) form. The formation of these nano‐/microparticles is confirmed by transmission electron microscopy (TEM) and dynamic light scattering (DLS) experiments in addition to the confocal laser scanning microscopy (CLSM) measurements. These nano‐/microparticles exhibit relatively strong red emission. It is interesting to note that the direct cooling of the toluene/benzene solution of 1 to 0 °C leads to gel formation. Multivalent π–π interactions due to the dendron in 1 may be the driving‐force for the gelation. The UV light irradiation cannot destroy the gel phase, and in fact, the gel–gel transition is successfully realized. The purple‐blue gel exhibits relatively strong red fluorescence; moreover, the fluorescence can be reversibly switched by alternating UV and visible light irradiation. The results clearly indicate that the MC form after aggregation becomes more stable and fluorescent.

Rhodamine B selenolactone has been designed, synthesized, and characterized as a new fluorescent probe for imaging both Hg(2+) and Ag(+) in live cells to better understand their distinct toxicities to organisms. The probe is designed based on the fact that selenium has a strong affinity for mercury and silver, and is constructed by incorporating a Se atom into the spirocyclic structure of rhodamine. It exhibits a rapid and specific spectroscopic off-on response to Hg(2+) and Ag(+) instead of other species, with detection limits of 23 nM Hg(2+) and 52 nM Ag(+). Moreover, the probe is membrane-permeable, and can react with Ag(+) even in the presence of Cl(-) because of the higher affinity of Se than Cl(-) for Ag(+), which makes it of potential use for imaging not only Hg(2+) but also Ag(+) in live cells. This applicability has been demonstrated by imaging Hg(2+) and Ag(+) in Hela cells. It is observed that the reaction of Ag(+) with the probe inside the cells occurs much slower than that of Hg(2+), which is ascribed to the high concentration of cellular chloride ions inhibiting the formation of sufficient free Ag(+). The present finding is helpful to get an insight into the different interaction mechanism of Hg(2+) and Ag(+) with cells, and more applications of the probe may be expected for studying the behaviors of Hg(2+) and Ag(+) in various biosystems.