Design, synthesis, crystal structure and DFT analysis of (E)-N-(tert-butyl)-11H-benzo[4,5]imidazo[2,1-a]isoindol-11-imines with dual-state emission property

Abstract

Benzoimidazoisoindoles are key structural motifs, widely found in pharmaceutical drugs and functional materials. However, very few strategies have been developed for the synthesis of benzoimidazoisoindoles, which greatly limited their applications. Herein we report an efficient approach for synthesizing benzoimidazoisoindole derivatives via palladium-catalyzed tandem cyclization of 2-(2-bromophenyl)-1H-benzo[d]imidazoles and isocyanides. Various benzoimidazoisoindoles were prepared in 63–86 % yields under air atmosphere at 100°C. The benzoimidazoisoindoles were characterized by UV–vis, photo-fluorescence, 1H and 13C NMR and HMRS. Furthermore, the single crystal structure of compound 3aa was determined to be of monoclinic system, space group I2/a, with α = 17.0080(4), b = 5.89820(10), c = 29.3286(7) Å, β = 102.948(2)°, V = 2867.34(11) Å3, Dc = 1.276 g/cm3, Z = 8, F(000) = 1168.0, μ(Cu Kα) = 0.599 mm−1, R = 0.0373 and wR = 0.0961. Photophysical property tests demonstrated that the designed benzoimidazoisoindoles exhibited typical dual-state emission (DSE) phenomenon. Density functional theory (DFT) calculation was also conducted to help understand the relationship between electronic structures and photophysical properties. Modified skeleton, the fused system includes benzoimidazoisoindole ring based on the structure–property relationship helps to design new, more effective types of dual-state emission materials.