Unprecedented Rearrangement: Investigation and OLED Application of a Novel Class of Carbazolophanes

Since the development of the first organic light-emitting diodes (OLEDs) over 30 years ago, there has been tremendous progress so that OLED displays are nowadays produced in a wide variety of architectures, from flat, rigid components to flexible and even foldable variants. Luminescent materials based on the principle of thermally activated delayed fluorescence (TADF) are of particular interest, especially blue TADF emitters combining both high efficiencies and long device lifetimes. Chiral materials exhibiting circularly polarized luminescence (CPL) are highly sought after for information storage, encryption of data, and to build thinner and brighter OLED devices. Therefore, our main focus relies on the design and characterization of blue TADF emitters bearing [2.2]paracyclophane as planar-chiral framework.<br/><br/>As demonstrated by our group, the cyclophane enables TADF efficiently in through space conjugation of donor (D) and acceptor (A), and induces higher torsion angles to bridging units when being employed as (1,4)carbazolophane donor leading to lower ΔEST and higher PLQYs.^[1-2]The ring-closure of carbazoles through C−H activation has been widely examined. During our synthesis of paracyclophane-fused carbazoles, we encountered the formation of [2]paracyclo[2](1,7)carbazolophane isomers through C−C bond breakage. These novel planar-chiral (1,7)carbazolophane building blocks offer unique structural features that significantly differ from the [2.2]paracyclophane core. The structure is confirmed by X-ray analysis while NMR spectroscopic results give insight into the aromatic character. Based on this new backbone, D-A-type TADF emitters are prepared and the influence of various substituents on the photophysical properties evaluated. Furthermore, the chiroptical and optoelectronic properties are investigated, supported additionally by computational calculations.<br/><br/>[1] E. Spuling, N. Sharma, I. D. W. Samuel, E. Zysman-Colman, S. Brase, <i>Chem. Commun. (Camb.) </i><b>2018</b>, <i>54</i>, 9278-9281.<br/>[2] N. Sharma, E. Spuling, C. M. Mattern, W. Li, O. Fuhr, Y. Tsuchiya, C. Adachi, S. Bräse, I. D. W. Samuel, E. Zysman-Colman, <i>Chem. Sci. </i><b>2019</b>, <i>10</i>, 6689-6696.