Divergent Synthesis of B, N, B-doped [4]Helicenes as Efficient Luminescent Materials

Abstract

We herein developed a synthetic method to access new B, N, B-doped derivatives of [4]helicene in three steps from commercially available starting material. The key synthetic step comprises in an advanced version of a Friedel Crafts Borylation and allows the decoration of the B, B´ positions with various electron withdrawing and electron donating groups in a highly divergent manner. All 7 derivatives were bright luminophores with emission colours ranging from sky blue to yellow and low singlet triplet energy gaps ΔEST between 130 meV and 190 meV. Furthermore, donor substitution enabled a rare temperature turn-on fluorescence which, in combination with the low ΔEST rendered the corresponding compounds as promising candidates for thermally activated delayed fluorescence (TADF).