Tetra (C₆₀) lanthanum phthalocyanine: design, synthesis and investigation of the third-order nonlinear optical...

The construction of molecules with effective photoinduced intramolecular electron transfer (PET) and energy transfer (ET) processes is critical for the enhancement of the nonlinear optical (NLO) properties. A novel D-π-A type compound, namely tetra (C₆₀)-LaPc, has been constructed from a molecular design perspective, wherein tetra-formyl phthalocyanine is used as a donor, four C₆₀ as acceptors and the phenylacetylene group is introduced into it as π-electron bridge, which can increase the molecular conjugation, reduce the spatial site resistance and expand the coplanarity of the molecule, thus making the intramolecular charge transfer easier. Tetra (C₆₀)-LaPc achieves excellent NLO properties with a giant nonlinear absorption coefficient (45 cm GW^-1 and large third-order susceptibility (4.05 × 10^-10 esu), which are superior to those of LaPc and C₆₀. In addition to exhibiting a superior nonlinear optical response at 532 nm compared to the single component, tetra (C₆₀)-LaPc also broadens the limiting range to the near-infrared region, showing a significant enhancement of the optical nonlinearity at 1064 nm. This can be attributed to the synergistic effect of the different non-linear absorption mechanisms between C₆₀ and LaPc and the efficient PET process.