Large optical nonlinearities of conjugated porphyrin polymers in the near infrared

The optical nonlinearities of porphyrin polymers were investigated in the telecommunications band: large values, slow kinetics in solutions revealed efficient optical limiting while large values, fast kinetics in films suggested ultrafast applications should be possible. © 2008 Optical Society of America

Large optical nonlinearities of conjugated porphyrin polymers in the near infrared

The optical nonlinearities of porphyrin polymers were investigated in the telecommunications band: large values, slow kinetics in solutions revealed efficient optical limiting while large values, fast kinetics in films suggested ultrafast applications should be possible. © 2008 Optical Society of America

Two methods for amplifying the optical nonlinearity of a conjugated porphyrin polymer: Transmetallation and self-assembly

A new soluble conjugated metalloporphyrin polymer has been synthesised as its complex with zinc(II), lead(II) and copper(II) and as the free-base. The zinc complex aggregates in non-coordinating solvents, due to coordination of the amide side-chains to the zinc centres. These aggregates dissociate on addition of pyridine to give single-strand complexes; the dissociation process displays an amazingly high positive cooperativity (Hill coefficient: n H = 3.2 at 50% sat., rising to 11.5 at 95% sat.). The zinc polymer binds 4,4′-bipyridyl to form a double-strand ladder complex; this self-assembly process holds neighbouring porphyrins coplanar and increases the π-conjugation, resulting in a red-shift in the electronic absorption. Degenerate four wave mixing, at 1064 nm, was used to characterise the optical nonlinearity of these polymers. Both the real and imaginary parts of the third-order susceptibility χ(3) are strongly amplified in the lead(II) complex and in the double-strand assembly. We estimate that the two-photon absorption cross-section of the ladder complex is 5 x 104 GM per macrocycle at 1064 nm, which is an order of magnitude higher than the highest values reported for other chromophores, suggesting that these polymers may be relevant to a variety of applications including photodynamic therapy

Making conjugated connections to porphyrins: a comparison of alkyne alkene imine and azo links

A series of porphyrins 5-9 has been prepared, in which an aryl substituent is linked to the porphyrin via azo, imine, alkene and alkyne bridges. The strength of aryl-porphyrin electronic coupling in these systems was evaluated from the red shift and intensification of the Q band absorption and emission spectra, and from the incremental red shift on changing from the phenyl to a 4-nitrophenyl substituent. The azo link provides the strongest electronic communication between the porphyrin and the benzene ring. The crystal structures of azo compounds 5a and 5c show that the porphyrin and benzene rings are almost coplanar, whereas imine 7a and alkene 8a are significantly twisted in the solid state. Imine and alkyne linked porphyrin dimers 18 and 23 were also synthesized; the alkyne-linked dimer is much more conjugated than its imine-linked analogue

A robust method to heterogenise and recycle group 9 catalysts

This paper provides a viable, reproducible and robust method for immobilising hydroxyl tethered iridium-rhodium complexes. The materials have been shown to be both effective and recyclable in the process of catalytic transfer hydrogenation with minimal metal leaching

Synthesis and third order nonlinear optics of a new soluble conjugated porphyrin polymer

The synthesis of a new soluble conjugated porphyrin polymer 4 is reported. The MALDI TOF mass spectrum shows the presence of oligomers with up to 13 repeat units and GPC gives a Mn of 53 kDa. The electronic absorption spectra of this polymer exhibit an intense Q band at 800 nm in solution and 853 nm in the solid state, demonstrating a high degree of conjugation. Electroabsorption spectroscopy shows that thin films of 4 have lower resonant third order NLO susceptibility than our previous conjugated porphyrin polymer 2, whereas closed z-scan measurements indicate that the off-resonance real susceptibility, at 1064 nm, is exceptionally large for both polymers (χ(3)R =-2 × 10-16 m2 V-2). Open z-scan measurements were also made at 1064 nm, demonstrating that the two polymers exhibit similar nonlinear absorption at this wavelength (β= 1 cm GW-1 at 0.2 mM concentration)

Organic materials for all-optical signal processing and optical limiting

Third-order nonlinearities and optical switching and limiting figures of merit are reported for several conjugated organic materials. Polymethines with large real to imaginary hyperpolarizability ratios and conjugated polymers with strong nonlinear absorption will be discussed. © 2010 Optical Society of America

Toward the realization of practicable materials for χ(3) based photonic applications

Two different routes were taken to develop materials for use in all-optical signal processing applications. Both systems exhibited large ultrafast nonlinearities, transparency in the near-infrared, and good processability for integration into photonic devices. © 2006 Optical Society of America