Synthesis and photophysical properties of different generations of poly(ester-amine) dendrimers with focal 4-amino-N-benzylphthalimide (4-ANBP) as the core were studied. The lambda(abs)(max) of dendronized 4-ANBP was nonsensitive to the solvents used and located at 334 nm, while that of bare 4-ANBP was very sensitive. The fluorescence behaviors of dendronized 4-ANBPs showed much dependence on the generation of the dendrimers used and the media. As compared with bare 4-ANBP, the fluorescence intensity of 3 (G1.0), 5 (G2.0), 7 (G3.0), and 9 (G4.0) in methanol was reduced to 6.2-, 26-, 50-, and 56.5-fold, respectively, and had a 83 nm blue shift. The corresponding fluorescence quantum yields were also measured (4-ANBP-0.12, 3-0.017, 5-0.0042, 7-0.0028, 9-0.0016). Addition of sulfuric acid to the methanol solution of 9 (3.27 x 10(-5) M/L), resulted in a strong fluorescence, and the fluorescence intensity was amplified 181 times. Acid titration experiments showed that all of the tertiary amines in 3, 5, and 7 were protonated, but only 12 in 15 of the tertiary amines in G4.0 delta 9 were protonated. Repeated acid-base titrations caused the fluorescence to switch on and off. After many cycles of acid-base titration. Slight changes in fluorescence intensity were observed.