A novel blue fluorescent 4-(1,2,2,6,6-pentamethylpiperidin-4-yloxy)-1,8-naphthalimide pH chemosensor based on photoinduced electron transfer

Three, blue emitting 2,2,6,6-tetramethylpiperidin-4-yloxy-1,8-naphthalimides 1–3 were configured as “fluorophore-spacer-receptor” systems. The photophysical characteristics of the dyes were investigated in water/DMF (4:1, v/v) solution. 1,8-Naphthalimide 1, which lacks the “lower” amino receptor, and compound 2, containing a secondary amino receptor at 1,8-naphthalimide 4-oxy moiety, did not show significant changes in emission properties as a function of pH. In contrast to compounds 1 and 2, 4-(1,2,2,6,6-pentamethylpiperidin-4-yloxy)-1,8-naphthalimide 3 displayed “on–off” switching in its fluorescence over a wider pH scale. From the luminescent changes pKa value of 8.63 was determined. This indicates that the chemosensor 3 would be able to act as highly efficient “off–on” fluorescent switcher for pH.