Experimental and theoretical study of the interaction of 3-carboxy-5,6-benzocoumarin with some 1,2,3,4,5,6,7,8-octahydroacridines and the corresponding N-oxides

The interaction of 3-carboxy-5,6-benzocoumarin (BzCum) with 1,2,3,4,5,6,7,8-octahydroacridine (OHA), 9-amino-1,2,3,4,5,6,7,8-octahydroacridine (H2N-OHA) and the corresponding N-oxides (OHA-NO and H2N-OHA-NO) was studied by fluorescence (steady state, time resolved) and absorption spectroscopy. The analysis of the fluorescence data in terms of Stern–Volmer plots indicated a predominant dynamic quenching for OHA and OHA-NO, and a more complex process for H2N-OHA and H2N-OHA-NO. The dynamic process was assigned to a photoinduced electron transfer (PET) from the acridine derivatives to the excited state of BzCum. The application of the Rehm–Weller–Marcus theory leads to a good agreement with literature data and allows for the estimation of the solvent organization energy. The presence of the PET mechanism was also supported by DFT results. The absorption spectra evidence the formation of a ground state complex assigned to a hydrogen bond complex involving the carboxylic hydrogen of BzCum.

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• Steady state and time resolved Stern–Volmer plots for 3-carboxy-5,6-benzocoumarin in presence of octahydroacridines.
• Dynamic quenching due to photoinduced electron transfer rationalized by Marcus theory and sustained by DFT calculations.
• Static quenching by ground state hydrogen bonded complex formation.