Synthesis and Characterization of Atropisomeric Bis-arylboryl-Carbazoles for use in CP-OLEDs

This work presents the synthesis and characterization of two functionalized atropisomeric amino-boranes. The two products are composed of a boron atom bonded with three different aryl groups: a mesityl substituent, a 2-trifluoromethyl-toluyl substituent and an asymmetrically substituted carbazole moiety. A methacrylate group was installed on the carbazole scaffold with and without an alkyl “spacer” in between. We performed an extensive computational analysis to gather predictions on the energies and peculiar geometries of the ground states, on the energies related to the many transition states that allow stereoisomerization, on the fluorescent and solvatochromic properties and lastly on circularly polarized luminescence. The synthesis was followed by CSP-HPLC, separating the four atropisomers of each product. The single atropisomers underwent two kinetic studies to experimentally determine the two energy barriers for stereoisomerization. Through Dynamic HPLC we studied the racemization kinetics and via Dynamic NMR the E-Z interconversion kinetics. For each atropisomer we determined the absolute configuration by matching its ECD spectrum with the ones predicted from the computational study (TD-DFT). Fluorescence was visually verified by placing the products under a 366 nm UV light.