We apply the non-empirical parameter tuning method proposed by Baer et al. to the CAM-B3LYP functional for the excitation energies of photochromic diarylethene derivatives in the closed- and open-ring isomers. Using the tuned parameter set, the time-dependent density functional theory calculations are found to well reproduce the experimental UV–Vis spectra with the same quality as our previous calculations with the parameter set obtained by referring the experimental values. These results demonstrate the performance of this parameter tuning method in the CAM-B3LYP functional for the excitation energies of unknown systems without any experimental data.