Nonlinear optical properties of both sulfonated- and halogen-substituted phenyl porphyrins with the effect of mono or bis halogen substitution and of protonation at different pH values on picosecond pulse trains generation

We studied the nonlinear dynamical propagating of picosecond pulse trains in sulfonated porphyrins. The sulfonated porphyrins were synthesized with one or two halogens (fluorine or chlorine) in phenyl rings and macrocycle protonation. One pulse train contains 25 subpulses with 70 ps width and 13.2 ns spacing. The effects of protonation at different pH values on the optical limiting behaviours of sulfonated porphyrins were also studied in this work. The energy structures of porphyrins were simplified to five-level models and Crank-Nicholson numerical method was applied to solve rate equations coupled with two-dimensional paraxial field. The results show sulfonated porphyrins are terrific optical limiters. Two halogens in phenyl rings would improve the optical limiting effects of porphyrins compared to the case of only one halogen in phenyl rings. Besides, nonprotonated sulfonated porphyrins in neutral solution with pH=7.0 show the lowest energy transmittances. But when the intensity of pulse train is strong, protonated sulfonated porphyrins in acidic solution with pH=1.4 show extremely fast growing optical limiting behaviours.