Access to Sondheimer-Wong Diyne-Embedded Diaza[7]helicene with High Dissymmetry Factor Via Spontaneous Valence Isomerization

The synthesis of Sondheimer-Wong diyne-fused diaza[7]helicene was achieved through spontaneous valence isomerization, which was a key step. Crystallographic analysis resolved the diaza[7]helicene's absolute configuration. The P,P- and M,M-enantiomers were separated by chiral HPLC and further characterized by CD and CPL spectroscopy. The obtained aza[7]helicene shows high dissymmetry factors with a g_abs of 0.046 (608 nm) and a g_lum of 0.0138 (693 nm). Theoretical calculation revealed that the Sondheimer-Wong diyne integration suppressed |μ| and enhanced |m| resulting in the high g factor.