Modulation of dual fluorescence modes and emissions of 2-(1,4-dioxo-1,4-dihydro-naphthalen-2-yl-amino)benzoic acid

Intra-molecularly hydrogen bonded compound 2-(1,4-dioxo-1,4-dihydronaphthalen-2-yl-amino)benzoic acid (ANQ) shows emission at single wavelength upon excitation in UV-region whereas it shows dual fluorescence emissions on excitation in visible region. Such emissions depend on solvent, concentration and pH. Solvent dependent structural changes of ANQ are reflected in solution studies carried out by 1HNMR, UV visible and fluorescence spectroscopy. DLS study has showed that in addition to monomers, self-assemblies with 415 nm average sized particles are formed in DMF solution. HOMO-LUMO of three tautomeric forms of the compound was calculated by DFT using CAMB3LYP/6-31 G(d,p) as basis set shows that naphthoquinone form has about 86.30 kJ/mol higher stability over an imino-quinone form. From various studies relating concentration dependence, pH, life-time, study on dual-emissions caused by visible excitation has established the observed emissions to originate from aggregation contributing as charge-transfer and deprotonated species. Whereas the single emission caused by UV-excitation occurs through excited state intra-molecular proton transfer. (C) 2017 Elsevier B.V. All rights reserved.