Abstract：N, N'-bi(L-phenylalanine amine)-perylene-3,4; 9,10-dicarboxylic diimide(PDCDA)was synthesized and characterized. The absorbance and fluorescence of PDCDA (10-5 mol/L) in aqueous solution were studied by varied pH values. The mechanism of the fluorescence indensity change was also discussed. And a fluorescent pH sensor was designed with PDCDA. It was water-soluble and had high fluorescent quantum yield. The fluorescence intensity of PDCDA was strongly dependent on pH, which was strong and stable in alkaline or neutral solution and was weakened in acid solution. The fluorescence intensity of PDCDA changed obviously even in a small pH range. The π-π stacking caused by pH led to the change of flourescence spectrum and absorption spectrum．The PDCDA can be used as a fluorescent pH sensor and the pH detection range was 3.8~6.3.
