Electron Push-Pull Effects in 3,9-Bis(p-(R)-diphenylamino)perylene and Constraint on Emission Color Tuning

A series of perylene-based donor-acceptor-donor (D-A-D) compounds, 3,9-bis(p-(R)-diphenylamino)perylene (R: CN (2a), F (2b), H (2c), Me (2d), and OMe (2e)), was synthesized using 3,9-dibromoperylene with p-(R)-diphenylamine, and the intramolecular charge transfer (ICT) on the D-A-D system with regard to the electron push-pull substituent effect was investigated. By introducing various p-(R)-diphenylamine derivatives with electron-donating or electron-withdrawing R groups, the energy band gaps of the D-A-D compounds were systematically controlled and the emission colors were efficiently tuned from green to red. As expected, the steady state emission spectra of all D-A-D compounds were observed, as well as the emission color controlled, depending on the Hammett substituent constants (σ_p). In the Lippert-Mataga plots, a different charge-transfer character was observed depending on the electron push-pull substitution, which showed gradually increased ICT characters from the electron-withdrawing to donating substitution. However, exceptionally, the strong electron-withdrawing group of CN-substituted 2a did not correlate with the other R group compounds. From the experimental data and density functional theory calculations, we assume that there is a constraint on emission color tuning to generate higher energy of blue emission in the D-A-D molecular system, due to the reverse charge-transfer property caused by the strong electron-withdrawing group.