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This paper analyzes the substituent effect (SE) on the photo-physical process of bis-1,10-phenanthroline copper(I) complexes to provide information that may eventually be useful in designing molecular machines based on this metal. This metal complex's ground and excited states were calculated, including the vertical, adiabatic, and intersystem crossing points (ISCP). Ab Initio Molecular Dynamics was used to find the time when the ISCP appears. The integrated properties of electron density allowed to detection of SE on the metal-ligand electron transfer and the dihedral angle between the ligands. The properties of the atomic graph permitted the analysis of SE on the equatorial coordination sites. [Display omitted] • Substituents modulate the electron transfer after the photo-excitation. • The electron transfer alters the molecular geometry change. • The The electron transfer determines the dihedral angle change. • Electron-withdrawing group produces larger electron flux. • Greater electron flux produces stronger Cu–N bonds and faster crossing points. [ABSTRACT FROM AUTHOR]

• Full characterization of NiII( tpa ) complexes gives information about its electronic structure which corelates with electrochemical behavior. • NiII( tpa ) complexes presented tunable redox potential for the NiII/NiI reduction. • NiII complex with more negative redox potential presented the high catalytic activity for CO 2 reduction. • Theoretical approach was useful for the analysis and description of electrochemical mechanisms. In this paper, we report the synthesis, characterization, as well as electrochemical, spectroelectrochemical, and density functional theory (DFT) calculations of a series of novel NiII complexes with a flexible tetradentate ligand, tris(2-pyridylmethyl)amine) ( tpa ). The complexes [NiII( tpa )(H 2 O)(MeCN)](BF 4) 2 , [NiII( tpa )(NO 3) 2 ], and [NiII( tpa )Cl 2 ] were studied for their ability to electrochemically reduce CO 2. These complexes were compared with the tris-chelate complex [Ni(bpy) 3 ](BF 4) 2 to understand the role of flexible tetradentate ligands containing a pyridinic ring in the electrochemical reduction of CO 2. Spectroelectrochemical experiments and theoretical studies were performed to rationalize the electrochemical reductions occurring and to predict the redox potential and pathway of CO 2 reduction. The electrochemical behavior of Ni(II) complexes with the ligand tris(2-pyridylmethyl)amine) was studied, in order to explore its ability to reduce electrochemically CO 2. Theoretical studies allowed to rationalize where the electrochemical reductions occur and predict redox potential and the pathway of CO 2 reduction. [Display omitted] [ABSTRACT FROM AUTHOR]