Synthesis and photochemical properties of a benzoacridone-containing fluorescent amino acid (badAla) which is photo-durable and excitable by widely applicable 488 nm lasers was described. The amino acid carries a relatively small fluorophore that shows absorption around 450-500 nm, emission above 500 nm with a high fluorescence quantum yield (0.65), and relatively long fluorescence lifetime (17 ns). BadAla can be used in solid-phase peptide synthesis without any precaution. A peptide-containing badAla was used to measure caspase activity via fluorescence resonance energy transfer (FRET).