Complexation studies of chlorophyll a with trinitro substituted fluorene derivates

Ground and excited state complexes of chlorophyll a from spinach with fluorene and trinitro substituted fluorene derivatives have been studied via absorption and fluorescence spectroscopy. Solvent effects on the binding of chl a to these fluorene molecules have been monitored in acetonitrile and dichloromethane at ambient temperature. The association constants (Ka) and the Stern-Volmer constants (Ksv) of the investigated complexes were larger in acetonitrile. Molecular modeling results of these systems suggest that the total binding energy of chl a/acceptor complex is dependent on the long-range (dispersion and electrostatic) interactions. Free energies of chl a/acceptor systems scale with the acceptor's dipole moment, electron affinity and dispersion interactions.