Synthesis and molecular properties of methoxy-substituted diindolo[3,2-b:2′,3′-h]carbazoles for organic electronics obtained by a consecutive twofold Suzuki and twofold Cadogan reaction

Abstract

A set of methoxy-substituted diindolo[3,2-b:2′,3′-h]carbazoles has been synthesized by twofold Suzuki–Miyaura, Cadogan and N-alkylation reactions starting from N-hexyl-2,7-dibromo-3,6-dinitro carbazole. Microwave accelerated reactions ensure a rapid straightforward and step-ecomomic assembly of the diindolo[3,2-b:2′,3′-h]carbazole framework. Besides the parent diindolo[3,2-b:2′,3′-h]carbazole four new methoxy-group bearing derivatives were obtained and their molecular properties were investigated by thermal, photophysical and electrochemical means. Dichloromethane solutions of the diindolocarbazoles display with respect to the methoxy-group substitution pattern bright photoluminescences covering the blue to green spectra with quantum yields of ϕ_F = 0.20–0.27. Notably, the N,N,N-tri-n-hexyl-1,4,9,12-tetramethoxy diindolo[3,2-b:2′,3′-h]carbazole exhibits a remarkable aggregate induced excimer-type luminescence (^emλ_max = 562 nm, ^solidϕ_F = 0.14) in the solid state resulting in bright yellow light emission, whereas the parent non-substituted compound and the other methoxy-substituted derivatives show poor photoluminescence from the solid state. HOMO/LUMO energy levels were determined by means of electrochemical and photophysical methods and were compared to those obtained by computational methods using B3LYP/6-31G(d) DFT calculations with a Polarisable Continuum Model (CPCM) for the solvent CH₂Cl₂. Good linear correlation was observed between calculated and experimentally measured values, and the correlations were used to estimate experimental HOMO/LUMO energy values of still non-synthesized heteroatom extended heteroacenes.