Nitric oxide (NO) is a gaseous, free radical, which plays a role as an intracellular second messenger and a diffusible intercellular messenger. To obtain evidence for NO function in vivo, 1, 3, 5, 7-tetramethyl-8-(4′-aminophenyl-N-(2′′-amino)-phenzyl)-difluoroboradiaza- s-indacene (TMAPABODIPY) was designed and synthesized as a fluorescent probe for nitric oxide, which features high photostability and no pH dependency over a wide pH range. ...