The synthesis and the structural and spectroscopic characterization of nonfluorescent, pyrene-based cyclic o-quinodimethanes are reported. These compounds react efficiently with nitric oxide (NO) in a formal cheletropic manner, by which the fluorescent aromatic pyrene system is regenerated. The NO trapping capabilities and kinetics of the fluorescent nitric oxide cheletropic traps (FNOCTs) are assessed in THF and buffered aqueous solution by ESR, UV/Vis, and fluorescence spectroscopy, by employing NO solutions and NO released from N-diazeniumdiolates (NONOates). Prototypal biological applications include the quantitation of NO production from cultured rat alveolar macrophages and the endothelium of porcine aorta, which demonstrate a sensitivity for NO detection in the nanomolar range.