Synthesis, spectroscopic and DFT theoretical studies on the hydrogen bonded charge transfer complex of 4-aminoquinoline with chloranilic acid

Abstract

New charge transfer hydrogen bonded complex between the electron donor 4-aminoquinoline (4AQ) with the π acceptor chloranilic acid (CLA) has been synthesized and characterized using a variety of physico-chemical techniques. Experimental work included the use of UV–vis spectroscopy to recognize of the complex formation in different solvents included acetonitrile (AN), methanol (MeOH) and ethanol (EtOH) through the appearance of new broad absorption band with λmax in the 500–550nm region. Photometric titration and Job's methods of continuous variations were carried out to shed more light about the molecular composition of the formed complex in solution where 1:1 (donor:acceptor) complex was obtained. Electronic spectral data were further analyzed in terms of formation constant, molar extinction coefficient, spectroscopic and analytical parameters of the formed complex. The solid 1:1 complex was synthesized and its molecular structure was characterized by elemental analysis where 1:1 (donor:acceptor) complex was produced, in agreement with that in different solvents. NMR and IR spectroscopy were used for further analysis of the solid complex where both hydrogen bond and charge transfer were evident in its molecular composition. The experimental studies were complemented by quantum chemical calculations at DFT/B3LYP level of theory. Electronic structure was investigated by TD-DFT method and the description of frontier molecular orbitals and the location of electron density were introduced. It has been confirmed that stability of the formed complex arises from charge transfer and hydrogen bonding interactions in the complex structure. Furthermore, the TD-DFT showed that the experimentally characterized broad absorption band of the complex is a combination of two electronic transitions at 476 and 650nm of π-π⁎ and n-π⁎, respectively. In addition, the red shift of λmax of the complex compared with the reactants confirming the strengthening of the formed OH…N in the excited state.