Carbon dots that exhibit near-infrared fluorescence (NIR CDs) are considered emerging nanomaterials for advanced biomedical applications with low toxicity and superior photostability and targeting compared to currently used photoluminescence agents. Despite progress in the synthesis of NIR CDs, there remains a key obstacle to using them as an in vivo theranostic agent. This work demonstrates that the newly developed sulfur and nitrogen codoped NIR CDs are highly efficient in photothermal therapy (PTT) in mouse models (conversion efficiency of 59%) and can be readily visualized by photoluminescence and photoacoustic imaging. The real theranostic potential of NIR CDs is enhanced by their unique biodistribution and targeting. Contrary to all other nanomaterials that have been tested in biomedicine, they are excreted through the body’s renal filtration system. Moreover, after intravenous injection, NIR CDs are accumulated in tumor tissue via passive targeting, without any active species such as antibodies. Due to their accumulation in tumor tissue without the need for intratumor injection, high photothermal conversion, excellent optical and photoacoustic imaging performance, and renal excretion, the developed CDs are suitable for transfer to clinical biomedical practice.

A mononuclear FeII complex that shows a high‐spin (S=2) paramagnetic behavior at all temperatures (with standard temperature‐scan rates, ≈1 K min−1) has, in fact, a low‐spin (S=0) ground state below 100 K. This low‐spin state is not easily accessible due to the extremely slow dynamics of the spin‐crossover process—a full relaxation from the metastable high‐spin state to the low‐spin ground state takes more than 5 h below 80 K. Bidirectional photo‐switching of the FeII state is achieved reproducibly by two selective irradiations (at 530–590 and 830–850 nm). The slow dynamics of the spin‐crossover and the strong structural cooperativity result in a remarkably wide 95‐K hysteresis loop induced by both temperature and selected light stimuli.

When located in octahedral environment, the iron(II) ion with a d 6 electronic configuration may adopt two different stable electronic states, namely, a diamagnetic low-spin (LS) state and a paramagnetic high-spin (HS) state, which both give rise to different magnetic, optical and electronic properties. So tuning the spin state of the iron(II) ion is significant and contributes to the development of amazing materials that can be used as molecular switches, sensors and display devices.[1] As is well established, the spin state depends on relative strength of spin paring energy (P) and splitting energy (D 0 ). If the former is much stronger than the latter, the HS state will be stabilised, and if D 0 is stronger then the LS state will be the ground state. If P and D 0 are comparable a spin crossover (SCO) may occur between the HS and LS state by external perturbations such as temperature, pressure or light irradiation. So the main task is to make a judicious choice of ligand, which can impose a proper ligand-field strength.[2] However, in reality, the spin state of the iron(II) ion is quite sensitive to even more subtle changes such as solvent molecules, [3] polymorphism [4] and counterions. [5] As one of the best representatives of switchable molecules, SCO materials have attracted considerable interest in the chemistry and materials fields. Current work mainly focuses on the enhancement of cooperativity, which results in an abrupt transition and a wider thermal hysteresis.[6] Another promising research area, but with few examples, [7] is the combination of magnetic-exchange and spin-transition (ST) phenomena in the same molecule or polymeric network, which could eventually afford new switching materials with considerable amplification of the response signal.[1d]Much more work should be done to expand our knowledge of spin electronics.To induce a ST, the most common method is by varying the temperature. However, light-and pressure-induced SCOs play an increasingly important role owing to their potential applications as optical and pressure switches, for example. Moreover, the latter two methods are not restricted to thermal SCO compounds: LIESST (light-induced excited spinstate trapping) may also be observed in LS compounds, whereas HS compounds may experience STs with the application of external hydrostatic pressure.Although there are many examples that exhibit thermal STs, rare spin-crossover clusters of iron(II) have been found to exhibit a mixed-spin structure and synergy between ST and magnetic interaction. Fortunately, by introducing counterions, we have successfully tuned the spin states of two apical iron(II) ions in the pentanuclear [{Fe II