One‐Pot Synthesis of Highly Emissive Dipyridinium Dihydrohelicenes

Condensation of a pyridyl‐2‐carbaldehyde derivative with 2‐(bromoethyl)amine hydrobromide gave tetracyclic pyrido[1,2‐ a ]pyrido[1′,2′:3,4]imidazo‐[2,1‐ c ]‐6,7‐dihydropyrazinium dications in excellent yields. Crystal structures and NOE data demonstrated the helical character of the dications, the dihedral angles between the two pyrido groups ranging from 28–45°. An intermediate in the synthesis was also characterized. A much brighter emission compared to literature helicenes has been found, with quantum yields as high as 60 % in the range of λ =460–600 nm. Preliminary cytotoxicity studies against HT‐29 cancer cells demonstrated moderate‐to‐good activity, with IC 50 values 12–30× that of cisplatin.