[2,2]paracyclophane-bisphthalocyanines: non-classical push-pull systems for second harmonic generation

The EFISH and HRS responses of a push-pull bisphthalocyanine-[2,2]paracyclophane compound have been measured at 1.9 and 1.06 μm, respectively, obtaining a remarkably high hyperpolarizability β HRS value. Since the two electronically different phthalocyanine chromophores are connected through a non π-conjugated and rigid [2,2]paracyclophane spacer, this result implies an efficient through-space intramolecular charge transfer between them. The results have been compared to that of structurally related, unsymmetrically substituted phthalocyanines 2-5, bearing either [2,2]paracyclophane or phenyl substituents. In these cases, the [2,2]paracycloplane does not play a significant role in the NLO response, being that the nature of the peripheral sustituents on the phthalocyanine is the most influent structural feature.