Quantum yield measurement of ICB used Methylene Blue (fF = 2.0% in water) as a reference standard. The concentrations of Methylene Blue and ICB were adjusted to an absorbance value of 0.065 at 620 nm. The fluorescence spectrum of each dye in H2O was obtained with excitation at 620 nm, with a slit width of 3 nm, the integrated area was used in the quantum yield calculation by the following equation: where η is the refractive index of the solvent, I is the integrated fluorescence intensity, and A is the absorbance at a chosen excitation wavelength. The measurement was conducted in triplicate with the reported quantum yield corresponding to the mean value ± standard deviation.