Spectrophotometric and fluorescence quenching studies of the charge transfer complexation of (4-dimethylamino-benzylidene)-(4,6-dimethyl-pyrimidin-2-yl)-amine with some organic acceptors

The interaction of organic acceptors such as tetrafluoro-1,4-benzoquinone (p-TFQ), tetrachloro-1,4-benzoquinone (p-TCQ), tetrachloro-1,2-benzoquinone (o-TCQ), tetrabromo-1,4-benzoquinone (p-TBQ), tetrabromo-1,2-benzoquinone (o-TBQ) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) with (4-dimethylamino-benzylidene)-(4,6-dimethyl-pyrimidin-2-yl)-amine (SB) as donor is studied spectrophotometrically and fluoremetrically in dichloromethane and trichloromethane. The association constant (K), thermodynamic parameters (ΔG°, ΔH° and ΔS°), oscillator strength (f), transition dipole moment (μ) and stoichiometric ratio are calculated using Benezi–Hildbrand's, Job and straight-line methods, respectively. The results reveal that the interaction between the donor and acceptors is due to π–π* transitions by the formation of radical ion pairs. The fluorescence quenching of SB with different organic acceptors is investigated. The results reveal that the fluorescence quenching obeys the static type mechanism via charge transfer complex formation in the ground state. The effect of temperature on the equilibrium constants of the CT complexes is also studied.