We believe that PET do occur and is the principal mechanism of NO photorelease, but is not visible in fluorescence and in calculations due to its low probability. Indeed, the estimated QY of NO photorelease, ΦNO, is 5.5×10 -4 for BODIPY-NOD-2. This value was obtained by using 488 nm laser and measuring the absorbed power and the amount of released NO. This value of ΦNO is indeed much smaller than the ΦF. Similar value for ΦNO (1.9×10 -3 ) was reported for NOBL-1 , which was successfully used for the photomanupulation of vasodilation. In contrast, fluorescence turn-on behavior was reported for photodonors having much higher ΦNO, for instance, ΦNO = 0.15 in .