The absence of fluorescence turn-on behavior may lead to the conclusion that PET does not occur in BODIPY-NODs. To additionally confirm this fact, we measured the fluorescence QY in a series of solvents having different polarity (Table ). A library of meso-substituted BODIPYs was studied in , and it was showed that their fluorescence, if quenched in polar solvents due to PET, turns on in non-polar solvents. In contrast, our results imply that the probability of PET is low. To analyze the NO release mechanism, we performed quantum chemical calculations for the singlet, triplet, and excited states of all compounds. The calculations were carried out in two functionals (CAMB3LYP, M06-2X) using different basis sets (6-31+G*, 6-311+G*, SPK-DZP).