Visible Light Chiral Photoinitiator for Radical Polymerization and Synthesis of Polymeric Films with Strong Chiroptical Activity

3-Methyl-4-aza­[6]­helicene
(A6H) enantiomers were synthesized and proposed as high-performance
visible light photoinitiators and/or photosensitizers for the free
radical polymerization (FRP) of (meth)­acrylates upon visible light
exposure using inexpensive and safe light-emitting diodes (LEDs) at
405 nm. Excellent polymerization initiating abilities were found,
and high final conversions were obtained. Remarkably, an exceptional
strongly enhanced chiral property of the polymer films was observed
in the presence of the enantiopure azahelicenes. This is the first
example of chiral properties introduced in polymer films by the photoinitiator
through photopolymerization processes. It is of high interest as these
latter are very fast and inexpensive polymerization techniques. Remarkably,
contrary to chiral properties introduced by using a combination of
commercial photoinitiator and chiral dopant, a dual behavior is found
here for A6H. A full picture of the involved chemical mechanisms is
given.