Fig. 1

a Synthetic route of PTZ-TQ molecule. b Absorption spectra of PTZ-TQ in tetrahydrofuran (THF) and in THF/H₂O with 95% water volume fraction (f_w). c Emission of PTZ-TQ in THF/H₂O (f_w, 0% to 95%) under 808-nm excitation. d Emission intensity ratio (I/I₀, calculated from (c) of PTZ-TQ under different f_w (I₀ is the emission intensity of PTZ-TQ in pure THF). e NIR-II fluorescence images of PTZ-TQ in THF/H₂O (f_w, 95%) and pure THF (50 μg/mL, 808-nm excitation, 1050, 1150, 1250 band-pass filter). f Signal intensity of PTZ-TQ and ICG through 1% intralipid solution (excitation 808 nm, 1050-nm band-pass filter). g Calculated HOMOs and LOMOs of PTZ-TQ [utilizing B3LYP functional and 6–31 g (d) basis set]