Fluorescent 4-(2,2,6,6-tetramethylpiperidin-4-ylamino)-1,8-naphthalimide pH chemosensor based on photoinduced electron transfer

Two isomeric 2,2,6,6-tetramethylpiperidinyl-4-amino-1,8-naphthalimides 5 and 7 were configured as fluorophore-spacer-receptor systems. Photophysical characteristics of the dyes were investigated in water/DMF (4:1, v/v) solution. Compound 5, which lacks the amino receptor at the 1,8-naphthalimide 4-amino moiety, did not show any changes in the emission properties as a function of pH. In contrast to compound 5, 4-(2,2,6, 6-tetramethylpiperidin-4-ylami no) - 1, 8 -naphthalimide 7 displayed on-off' switching in its fluorescence as a function of pH. From the luminescent changes pK(a) value of 8. 18 was determined. This indicates that the chemosensor 7 would be able to act as highly efficient off-on fluorescent switcher for pH. (C) 2006 Elsevier B.V. All rights reserved.