Figure 2.

Releasing ligand with NIR light makes IR700DX-dye hydrophobic causing loss of its fluorescence. (a) 0.5 μM IR700-dye in PBS was irradiated with NIR light, and imaged in white light using a 700 nm filter. Both the blue color in the tube and the 700 nm fluorescence decreased in a light-dose-dependent manner. (b) Mean 700 nm fluorescence intensity was decreased in a dose-dependent manner (n = 3). (c) Absorbance profile showed decrease of the absorbance at the Q-band at 690 nm of the silicon phthalocyanines (SiPcs). (d) Mass spectroscopy detected released ligand (C₁₄H₃₄NO₁₀S₃Si) only in the NIR-light-irradiated (16 J cm^–2) tube (0.1 mM IR700-dye in PBS). With isotopic peak analysis, the peak was matched to the ligand (C₁₄H₃₄NO₁₀S₃Si) (Figure S1). (e) Hypothesized change of chemical structure of IR700-dye with NIR light irradiation. NIR light irradiation causes IR700-dye releasing the ligand (C₁₄H₃₄NO₁₀S₃Si), which makes IR700 hydrophobic and creates aggregation. Along with the change from hydrophilic to hydrophobic solubility, the blue color of IR700 decreases, and aggregation appears, while IR700-fluorescence is lost, as shown in part a.