Charge transfer complexes formed by electron transfer processes are important components of many biochemical processes. Donor-acceptor complex formation between promazine and dopamine, serotonin and melatonin was investigated using experimental and computational methods. UV-Vis absorption, fluorescence spectroscopy and cyclic voltammetry measurements were carried out to investigate the intermolecular interactions and donor-acceptor properties. Geometry optimizations were completed at omega B97XD/6-31G(d,p) level and electronic transitions were performed by the time-dependent density functional theory with CAM-B3LYP, B3LYP, and omega B97XD functionals using 6-311 + + G(d,p) basis set. Complex formation with promazine is in the order as melatonin > serotonin > dopamine in water especially by H-bond formation. Experimental and calculated values for UV-Vis absorption spectra and HOMO, LUMO energies were compared and found in agreement in water. Serotonin was determined as the best donor among studied molecules forming H-bond and pi-pi* interactions with promazine. Investigated complexes may be useful for the design of organic-biological hybrid components acting as donor-acceptor systems.