Ultrafast charge transfer of stiboviologens for electrochromism and visible light-induced ?-amino C(sp³)-H functionalization

A series of antimony-bridged viologen derivatives, stiboviologens, were obtained by introducing an antimony atom into the viologen skeleton. By modifying them through N-alkylation and N-arylation, the optoelectronic properties of the stiboviologens were finely tuned. The stiboviologens displayed strong redox properties, high conjugation, and low energy gaps. Notably, the presence of the antimony atom significantly enhanced the ultrafast metal to ligand charge transfer (MLCT) process (to approximately 1 ps), as determined by femtosecond transient absorption studies. Leveraging their excellent optoelectronic properties, the stiboviologens were successfully applied in electrochromism and utilized as both photosensitizers and electron transfer agents for catalyzing ?-amino C(sp³)-H functionalization reactions including the oxidative cyclization reaction and cross dehydrogenative coupling reaction under visible light conditions. These findings highlight the potential of stiboviologens as promising materials in the field of optoelectronics and their versatile utilization in synthetic transformations.