Ratiometric sensors for the detection of metal ions have gained increasing attention due to its self-calibration tendency for the environmental effects. In this context, we have synthesized and characterized a dual emitting ratiometric Zn2+ probe (1) having acridinedione as a fluorophore and N,N-bis(2- pyridylmethyl)amine (BPA) as a receptor unit. Existence of two different conformation of the molecule with photoinduced electron transfer (PET) from amine moiety to the acridinedione fluorophore leads to dual emission, namely locally excited (425 nm) and anomalous charge transfer emission (560 nm) in aprotic solvents. In the presence of one equivalent of Zn2+, a 15-fold fluorescence enhancement in the locally excited state together with the quenching of charge transfer emission is observed. The intensity changes at the two emission peaks allow a ratiometric detection of Zn2+ under PET signaling mechanism. The utilization of PET process for the ratiometric fluorescence change will further signify the importance of PET mechanism in sensing action. Addition of Zn2+ to 1 in acetonitrile/water mixtures shows a single emission peak with fluorescence enhancement.
J. Phys. Chem. A 2011, 115, 14292–14299

Amidothiourea linked acridinedione derivatives selectively detect Hg2+ in unbuffered aqueous solution under broad pH range with both single- and two-photon excitation. The observed linear fluorescence intensity change allows the quantitative detection of Hg2+ in the concentration range of 22 nM–0.33 lM with the lower detection limit of 2 nM.
Chem. Commun., 2011, 47, 7695–7697

Acridinedione-based heteroditopic hosts 1a-c, which contain a flexible oxyethylene moiety as a metal ion binding site and amino hydrogen as an anion receptor unit, were synthesized and characterized. Metal ion and anion binding studies were carried out in different solvents to understand the solvent-induced selectivity of the metal ion binding and anion interactions. In acetonitrile, Ca2+ alone shows a binding with the oxyethylene unit and -OCH3 group, which results in a fluorescence enhancement without any spectral shift due to the suppression of the photoinduced electron transfer (PET) process. In chloroform, in addition to Ca2+, Na+ also shows a fluorescence enhancement with a 14 nm red shift in the emission maximum. 1H NMR titration studies confirm that the addition of Na+ does not involve binding at the oxyethylene moiety, while it shows a binding at the acridinedione carbonyl group and -OCH3 group, which results in the red shift and fluorescence enhancement, respectively. In the anion interaction studies, F- shows a neat deprotonation in polar aprotic solvents, whereas in chloroform, it shows a H-bond complex due to the lower anion desolvation energy. The present study clearly signifies the role of solvent in metal ion selectivity, which is an often unnoticed parameter in metal ion binding.
J. Phys. Chem. B 2011, 115, 84–92

Bisacridinedione-functionalized gold nanoparticles (bisADD-GNPs) were prepared and characterized. Bis- ADD is a flexible acyclic moiety and a specific Ca2+ sensor. Signaling of the binding events is achieved by the cation-induced folding of the bisADD-GNPs and the resultant fluorescence enhancement and visual color change are attributed to the suppression of photoinduced electron transfer (PET) through space and nano-Au aggregation. The selective binding of Ca2+ is clear from steady state fluorescence and TEM techniques.
Tetrahedron Letters 51 (2010) 3102–3105

A dual emitting acridinedione fluorophore, 9-(4-(dimethylamino)phenyl)-3,4,6,7,9,10- hexahydroacridine-1,8(2H,5H)-dione (DMAADR-1), was synthesized and its dual fluorescence behavior was found to be greatly affected by the presence of both transition metal ions and anions. Addition of transition metal ions results in the fluorescence enhancement in the locally excited (LE) state with the disappearance of charge transfer (CT) state by suppression of photoinduced electron transfer (PET) process. Whereas in the case of anions like acetate, phosphate and fluoride, a triple fluorescence is observed, corresponding to the LE state, PET promoted CT state and anion induced CT (AICT) state. Since the present molecule can act as heteroditopic host for both transition metal ions and anions, we have carried out simultaneous binding studies of metal ions and anions. These studies clearly proved the sequestering of the ions and thus tuned the fluorescence of DMAADR-1 between OFF–ON states.
Journal of Photochemistry and Photobiology A: Chemistry 208 (2009) 117–124