Large two photon absorption cross section of asymmetric Zn(II) porphyrin complexes substituted in the meso or β pyrrolic position by –CC–C6H4X moieties (X = NMe2, NO2)

A large two photon absorption (TPA) cross section of about 4000 GM is measured by Z-scan technique for a push–pull A–π–D Zn(II) porphyrin complex disubstituted in the meso position with strong donor and acceptor moieties. This result is compared to the lower TPA cross section of Zn(II) porphyrinates mono-substituted in the meso or β pyrrolic position with the same donor or acceptor substituents. The origin of such trend is discussed in terms of charge transfer processes, π delocalisation and resonance pathways.