A series of polycyclic aromatic hydrocarbon-substituted metal-free porphyrins: Substituent effect on two-photon absorption property

• The third-order nonlinear optical properties of naphthyl, phenanthrenyl, and pyrenyl substituted porphyrins have been investigated.
• Both the pyrenly-substituted porphyrin and the phenanthrenly-substituted porphyrin exhibit large two-photon absorption cross sections.
• The pyrenly-substituted porphyrin has the most excellent 2PA property because of the intramolecular fluorescence energy transfer.

The third-order nonlinear optical properties of a series of naphthyl, phenanthrenyl, and pyrenyl substituted porphyrins have been comparatively investigated by performing the femtosecond-pulsed Z-scan measurements. Due to the expanded π system, both pyrenly substituted porphyrin (1) and phenanthrenly substituted porphyrin (2) exhibit large two-photon absorption cross sections up to 4.26 × 104 GM for 1 and 1.36 × 104 GM for 2 at the wavelength of 800 nm. The pyrenly substituted porphyrin (1) has the most excellent two-photon absorption property because of the intramolecular energy transfer from the excited pyrene moiety to the porphyrin moiety in porphyrin 1. The results confirm that porphyrins conjugated with external π electronic systems can lead to the significant enhancement in the two-photon absorption cross-section values. This research provides a useful guideline to the design of efficient two-photon absorbing materials.