Scheme 2.

Simplified Jablonski diagram of (a) NI-PTZ-F and (b) NI-PTZ-F-O. The ¹LE state (¹[NI–PTZ–F–O]^*) energy is derived from the spectroscopic data (the intersection of normalized UV–vis absorption and fluorescence spectra). The triplet state (³[NI^−•–PTZ^+•–F–O]^*) energy is computed by the TDDFT method, which was performed at the B3LYP/6-31G(d) level of theory using Gaussian 09W. The ¹CS state (¹[NI^−•–PTZ^+•–F–O]^*) energy is obtained from electrochemical data in Table 4 (¹CS/³CS: 2J < 0.2 eV).