Theoretical study on the isomerization mechanism of azobenzene derivatives on graphene substrate

Abstract

This article investigates the isomerization mechanism of 3,5-dimethoxy-4-phenyldiazenyl-aniline (DMA) and 3,5-dimethoxy-4-phenyldiazenyl-aniline on graphene (Gr) substrate (DMA-Gr) at B3LYP/def2-svp level. The similarities and differences between the isomerization of DMA and DMA on graphene with different grafting density were explored. According to DFT calculations, DMA has two inversion models: N1 and N2 inversion. N1 isomerization pathway is closely related to the substituents on the benzene ring connecting to N3 atom, and N2 isomerization pathway is closely related to the substituents on the benzene ring connecting to N2 atom. The transition states TS1 and TS2 of the isomerization reaction were found. The isomerization pathway of DMA is more favorable towards N1 inversion. In addition, the isomerization mechanism of a single molecular azobenzene derivative with a graphene substrate(s-DMA-Gr) is similar to that of DMA with s-TS1 and s-TS2 transition states. Interestingly, the isomerization pathway is more favorable towards N2 inversion, which is different from that of DMA. Due to two DMA molecules on graphene substrate, the isomerization pathway is different from that of DMA. The transition states FTS1, FTS2, STS1 and STS2 of the isomerization reaction of DMA-Gr were found. Among them, the isomerization path of the first DMA molecule functional group is more favorable to adopt the N1 inversion with the energy barrier of 34.62 kcal/mol, then the second DMA molecule functional group also adopts the N1 inversion model with the energy barrier of 35.95 kcal/mol. The energy barrier of isomerization of DMA-Gr is higher than that of DMA, corresponding to a longer lifetime for DMA-Gr as energy storage materials.