Structure−Property Relationship for Two-Photon Absorbing Multiporphyrins: Supramolecular Assembly of Highly-Conjugated Multiporphyrinic Ladders and Prisms

Abstract

Two-photon absorption (TPA) phenomena of a series of single-strand as well as supramolecular self-assembled ladders and prisms of highly conjugated ethyne bridged multiporphyrin dimer, trimer, and star shaped pentamer have been investigated. The ligand mediated self-assembled supramolecular structures were characterized by UV-visible spectroscopy and small- and wide-angle X-ray scattering (SAXS/WAXS) analysis. The TPA cross section values of multiporphyrins increase nonlinearly from approximately 100 to approximately 18000 GM with an increased number of porphyrin units and elongated pi-conjugation length by virtue of charge transfer and excited-state cumulenic configurations. The observed opposite TPA behavior between their supramolecular ladder and prism configurations necessitates the importance of interstrand interactions between the multiporphyrinic units and the overall shape of the assembly. Furthermore, the diminished TPA cross section of the pentamer, despite the increased pi-conjugation resulting from duplex formation suggests that destabilizing the essential functional configurations at the cost of elongation of pi-delocalization pathway must cause unfavorable effects. We have also shown that one- and two-photon allowed energy-levels of linear multiporphyrins are nearly isoenergetic and the latter transition originates exclusively from the extent of pi-delocalization within the molecule. The identical TPA maximum position of the trimer and pentamer indicates that the TPA of the pentamer arises only from its basic trimer unit in spite of its extended two-dimensional pi-conjugation pathway involving five porphyrinic units.

Versatile Photophysical Properties of meso‐Aryl‐Substituted Subporphyrins: Dipolar and Octupolar Charge‐Transfer Interactions

“…The temperature dependence of p-NH 2 and m-NH 2 is similar to that observed for highly conjugated meso-alkynyl-substituted multiporphyrins. [46][47][48] In addition, the notable redshift of the Qlike band for p-NH 2 (21 nm) compared with m-NH 2 (2 nm) is attributable to the stronger electronic interactions of the para-aminophenyl group. Another important parameter is the full width at half-maximum (FWHM) of the absorption bands, which are obviously influenced by the meso-aryl group dihedral angle distribution.…”

Two‐Photon Absorption and the Design of Two‐Photon Dyes

“…There is a weaker dependence of S C on N e in the corresponding single-strand oligomers 22-25. However, Wasielewski, Kim and co-workers [58] showed that while the formation of a double strand enhances the 2PA cross-section of a conjugated porphyrin trimer, surprisingly formation of a triple strand, by using a tridentate ligand, has the opposite effect. It appears that 2PA in these arrays is still not well understood.…”

Zweiphotonenabsorption und das Design von Zweiphotonenfarbstoffen

“…[55] wo die Einphotonenabsorption vernachlässigt werden kann, aber einen Wert von d = 41 000 GM für das Tetramer. [57] [58] wiesen für ein konjugiertes Porphyrintrimer nach, dass die Bildung von Doppelsträngen den 2PA-Querschnitt erhöht, die Bildung eines Tripelstrangs mithilfe eines dreizähnigen Liganden aber einen entgegengesetzten Effekt hat. Die 2PA dieser Anordnungen lässt sich demnach noch nicht befriedigend erklären.…”