Investigation of anhydrous benz (f) ninhydrin, indanetrione and 5-methoxy indanetrione by electronic absorption and emission spectroscopy and computational chemistry methods Original Research Article

A comparative study of the low lying electronic states and photophysical aspects of the compounds anhydrous benz (f) ninhydrin (I), indanetrione (anhydrous ninhydrin) (II) and 5-methoxy indanetrione (anhydrous 5-methoxy ninhydrin) (III) having a cis vicinal cyclic triketo system (three adjacent carbonyl groups in the same plane) has been carried out using absorption, emission and excitation spectra in various solvents at different temperatures. AM 1 and CNDO calculations were carried out to find the ground state geometry and to confirm the assignment of various electronic states of I, respectively. An intramolecular charge transfer band in I has been detected and characterised by theoretical calculations. Solvent effect on the 1(n π∗) transitions of these compounds has also been studied. The characterisation of charge transfer complexes of II with various polynuclear aromatic hydrocarbons has been presented to show that a cis vicinal triketo system attached to an aromatic moiety can function as a potential acceptor. The position of the low lying electronic states of this class of compounds allows them to exhibit unusual 1(n π∗) fluorescence at room temperature. The compounds also exhibit (n π∗) phosphorescence in various solvents at 77 K.