Dual Modes and Dual Emissions of an Amino-Naphthoquinone Derivative.

3-(1,4-Dioxo-1,4-dihydronaphthalen-2-yl-amino)benzoic acid shows multiple tunable fluorescence emissions depending on solvent, pH and wavelength of excitation. Independent dual fluorescence emissions are observed while exciting compound 3-(1,4-dioxo-1,4-dihydronaphthalen-2-yl-amino)benzoic acid in UV-region or in visible region. In methanol at low concentration it shows both S1 -S0 emission and ESIPT emission at 307 nm and 480 nm. Whereas in concentrated solution S1 -S0 emission as well as dimer-like emission at 307 nm and 425 nm respectively are observed. Upon excitation in visible region, it shows two emission bands in visible region which are highly dependent on concentration and are attributed to charge transfer emission and emissions of anionic species. Modulations of these emissions by varying conditions are established.