Theoretical study on the molecular structure, intermolecular interaction and spectral features of 2-aminopyridine/ 2,3-dichloro-5,6-dicyano-1,4-benzoquinone complex

Abstract

Density function theory (DFT) was performed to study the structures and binding energies of the 2-aminopyridine(2-AP)/2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) complex. Four distinct stable conformers (denoted as S1–S4) were located and the bonding characteristics of these conformers were investigated with NBO and AIM analysis. It was revealed that S1 is formed by the edge(2-AP)-to-face(DDQ) linkage, which is stabilized by a moderate $${\upsigma }$$ – $${\uppi }$$ interaction and hydrogen binding interaction. S2 and S3 are formed by the face(2-AP)-to-face(DDQ) linkage through $${\upsigma }$$ – $${\uppi }$$ and $${\uppi }$$ – $${\uppi }$$ interactions, and S4 is constructed by the edge(2-AP)-to-edge(DDQ) linkage through halogen bonding and hydrogen bonding interactions. The electronic excitation energies of the two stable conformers, S2 and S3, were calculated with time-dependent DFT (TDDFT), which revealed that the 2-AP $$({\uppi })$$ $$\rightarrow $$ DDQ( $${\uppi }$$ *) charge transfer transitions in conformers S2 and S3 contribute to the two new charge transfer absorption bands which were experimentally observed at 598 nm and 557 nm for the 2-AP/DDQ complex in chloroform. Four probable structures of the 2-AP/DDQ complex were located by DFT calculation. The bonding characteristics between the two molecules of the complex were investigated by NBO and AIM analysis. Two new absorption bands observed in the UV–Vis absorption spectrum of the complex were attributed according to the TDDFT results.