Structures and properties of 1,7-disubstituted perylene tetracarboxylic diimides: The substitutional effect study based on density functional theory calculations

Density functional theory (DFT) calculations were carried out to describe the molecular structures, molecular orbitals, atomic charges, UV-vis absorption and IR spectra of 1,7-disubstituted-perylene-3,4;9,10-tetracarboxylic diimide (1,7-disubstituted PDI) with different substituents, namely unsubstituted PDI (PDI-0), 1,7-dimethylthio PDI (S-a), 1,7-dithiophenyl PDI (S-b), 1,7-dimethoxy PDI (O-a), 1,7-diphenoxy PDI (O-b), 1,7-dimethylamino PDI (N-a), 1-methoxy-7-methylthio PDI (OS-a), 1-phenoxy-7-thiophenyl PDI (OS-b), and 1-methoxy-7-methylamino PDI (ON-a). Good consistency was found between the calculated results and experimental data. The substitutional effects of the side groups on both the structure twisting and the electronic absorption spectra depend mainly on the linking atoms rather than the side groups as a whole. The charge distribution, the ionization energy (IE) and electronic affinity (EA) are found to be varied significantly along with the change of the electron donating abilities of the side groups. The effects of the side groups on the vibration spectra of these compounds are also discussed based on both the simulated and experimental results. The present work, representing the first systemic DFT study on the PDI derivatives, sheds further light on clearly understanding structure and spectroscopic properties of PDI compounds.