Synthesis, selective pH-sensing activity and logic behavior of highly water-soluble 1,8-naphthalimide and dihydroimidazonaphthalimide derivatives

This paper reports on the design, synthesis and fluorescence pH-sensing activity of a novel highly water-soluble 1,8-naphthalimide and its 9,10-dihydro-7H-imidazo[1,2-b]benz[d,e]isoqionolin-7-one derivative. The changes in the photophysical properties of the compounds as a function of pH were investigated in 100% aqueous medium. The 1,8-naphthalimide dye manifests “off-on” pH sensing properties based on photoinduced electron transfer, while its condensed heterocyclic derivative revealed ratiometric “off-on-off” fluorescence pH probe activity. Due to the two different “off”-states the dihydroimidazonaphthalimide derivative is able to execute the logical functions INH and XNOR and as such, to act as a magnitude digital comparator. The synthesized compounds show excellent selectivity toward protons over the representative transition metal ions (Co2+, Cu2+, Fe3+, Ni2+, Cd2+, Pb2+, Zn2+, Hg2+ and Ag+) is commonly used buffer solutions. The high water solubility and excellent pH selectivity of both probes as well as the ratiometric pH sensitivity of dihydroimidazonaphthalimide derivative may be beneficially for monitoring pH variations in complex samples.