Charge transfer complexes of 2-arylaminomethyl-1H-benzimidazole with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone: Experimental and DFT studies

Two new charge transfer complexes (L1,2DDQ; L1 = (1H-benzimidazol-2- ylmethyl)-N-phenyl amine, L2 = (1H-benzimidazol-2-ylmethyl)-(4-nitro-phenyl)- amine, and DDQ = 2,3-dichloro-5,6-dicyano-1,4-benzoquinone) have been synthesized and characterized by a variety of physico-chemical techniques. The experimental studies were complemented by quantum chemical calculations at DFT/B3LYP level of theory. Electronic structures were investigated by TD-DFT method and the descriptions of frontier molecular orbitals and the relocation of the electron density were determined. Stability of the molecule arises from hyperconjugative interactions, charge delocalization and hydrogen bonding has been analyzed using natural bond orbital (NBO) analysis. 1H NMR chemical shifts were computed at B3LYP/6-311+G(2d,p) level of theory by Gauge-invariant atomic orbital (GIAO) in DMSO as a solvent using the polarizable continuum model (PCM). Photometric titration was carried out to shed more light about the stoichiometry of the formed complexes in the solution. Spectral data were analyzed in terms of formation constant, molar extinction coefficient, oscillator strength, dipole moment, standard free energy, and ionization potential.