Reductive methylation of triphthaloylbenzene: Isolation and characterization of hexamethoxy-trinaphthylene and two unexpected trinaphthylene derivatives

[Display omitted] •Reductive methylation of triphthaloylbenezene was complicated.•Two unexpected products except for hexamethoxy-trinaphthylene were isolated.•X-ray crystallographic analysis of two compounds exhibit deformed cores.•Optical properties of three compounds were examined.•Adding DBU into a peculiar compound possessing hydroxy groups causes a color change. With the aim of developing new π-conjugated materials for application in electronics, the reductive methylation of triphthaloylbenzene is presented. Several new products are obtained: 5,6,11,12,17,18-hexamethoxy-trinaphthylene (1a) and two unexpected compounds, i.e., the corresponding monohydroxy-pentamethoxy-trinaphthylene (1b) and a peculiar trinaphtylene derivative (2) possessing hydroxy, methoxy, carbonyl, and ketal groups and a tetrahydrofuran moiety fused on the core. X-ray crystallographic analysis of 1b and 2 reveals that both compounds exhibit deformed frameworks. The investigation of their optical properties shows that the lowest-energy absorption bands for 1a and 1b are a shoulder band around 350 nm, whereas 2 gives rise to a one broad and weak band at 573 nm. All the molecules have negligible fluorescence. Addition of 1,8-diazabicyclo[5.4.0]undec-7-ene into a solution of 2 causes a color change from purple to olive brown, which renders it suitable as a pH indicator.