Fig. 4: CO₂-modulated fluorescence properties of H(40).

a UV absorption (purple) and fluorescence emission (blue) spectra of H(40) at 25 °C. Solid and dashed lines indicate spectra with and without CO₂ exposure, respectively. The excitation wavelength is 360 nm. The scale bar is 10 mm. b Impact of CO₂ exposure on the quantum yield (excited at 360 nm). c Fluorescence decay curves of H(40) with and without CO₂ exposure, measured under 360 nm excitation. The fluorescence lifetimes (τ) of H(40) with and without CO₂ exposure are 8.6 and 9.1 ns, respectively. d Visualization of CO₂ diffusion into selected H(n) sheets under UV irradiation. Here, circular sheets (8 mm in diameter) were sandwiched between glass plates and exposed to CO₂. The scale bar is 4 mm. e Thickness of the CO₂-cured region in the synthesized materials as a function of time.