Fig. 1. TTA-UC (a) and OPA-UC (b) Joblonski energy level diagrams

Fig. 2. Schematic diagram of the molecular structure of the azaanthracene derivative

Fig. 3. Absorption spectra (a) and fluorescence spectra (b) of azaanthracene derivatives

Fig. 4. Fluorescence lifetime curves of azaanthracene derivatives

Fig. 5. Schematic diagram of the energy levels of three sensitizers (PSF, SFT and MTV) and the annihilator

Fig. 6. Upconversion spectra of azaanthracene derivatives as sensitizer (10 μmol·L^-1) and DPA (1 mmol·L^-1)
Solvent: DCM/NPA=1/1, λ_ex= 532 nm

Fig. 7. Fluorescence quenching diagram of annihilator (DPA) to sensitizer
(a): PSF; (b): SFT (Sensitizer: 6 μmol·L^-1, Solvent: DCM, λ_ex=532 nm)

Fig. 8. OPA-UC spectrum (a) and the corresponding photos (b) of azaanthracene derivatives
Concentraction: 1×10^-5 mol·L^-1; Solvent: DMSO, λ_ex=655 nm

Fig. 9. The power density upconversion spectra diagram (a, b) and corresponding logarithmic linear diagram (c, d) of azaanthracene derivatives
(a): PSF; (b): MTV, concentraction: 50 μmol·L^-1, solvent: DMSO, λ_ex=655 nm

Fig. 10. Concentration-dependent upconversion spectra of azaanthracene derivatives
(a): PSF; (b): MTV, (solvent: DMSO, λ_ex=655 nm)

Fig. 11. Curves of upconversion efficiency for azaanthracene derivatives at different concentrations
Solvent: DMSO