New photosetting NLO-active polythiophenes with enhanced optical stability

A new molecular design strategy devoted to the obtainment of polythiophenes showing a second-order NLO response that is stable in time is reported and commented on. The adopted synthetic procedure, based on the functionalization of soluble and stable polymeric precursors, leads to a photocrosslinkable polymer which, after curing, shows a decay of the order parameter ϕ notably slower than in previously synthesized NLO-active polymers containing the same kind of chromophore. The curing conditions have been carefully monitored and optimized, since they not only influence the chain mobility, but also strongly affect the electronic delocalization of the polyconjugated backbone. Detrimental effects can, however, be avoided by using suitable functional groups in the side chains, acting as internal plasticizers without being sensitizers for the photobleaching process.