Determination of vertical ionization potential of nitroso-benzoimidazothiazole using charge transfer interaction with a series of acceptors.

This is the first report of UV-Vis spectral investigations of electron donor-acceptor complexes of bio active 3-Nitroso-2-phenylbenzo[d]imidazo[2,1-b]thiazole (BIT1) with chloranils, nitrobenzenes and fullerenes in DMSO medium. Well defined charge transfer (CT) absorption bands in the visible region have been sited. Oscillator strengths, transition dipole and resonance energies of the CT complexes have been estimated. Utilizing Mulliken's equation vertical ionization potential of BIT1 has been determined. A possible mechanism for the interaction between electronic subsystems of chloranils, nitrobenzenes, [60]- and [70] fullerenes with this benzoimidazothiazole compound (BIT1) have been discussed in comparing the parameters like degree of charge transfer and binding constant in polar DMSO. 1H NMR study helps to explain the mechanism well. Comparison of complexes is done with DFT/PW1PW91/6-31G* optimized gas phase geometries and FMO features of adducts.