Optical limiting of pentaazadentate complexes in solution for ps pulses

The passive optical limiters are of significant for protecting sensors and human eyes from high intensity laser The selection of materials is still the key point for optical power limiters. The optical limiting performances for five new pentaazadentate metal complexes with transmission of 0.45-0.70 in a 1 cm cell in tetrahydrofuran have been measured at 532 nm with 35 ps pulses, in which the reverse saturable absorption from the singlet->singlet excited state is responsible for the optical limiting. The optical limiting thresholds of pentaazadentate and benzopentaazadentate cadmium complexes at T/T-0 = 0.5 are 44 mJ/cm(2) and 146 mJ/cm(2) respectively, the lowest nonlinear transmittance for pentaazadentate complex I is 7.7 %, while the incident maximum fluence reaches to 881mJ/cm(2). The hounds of figure of merit-like are estimated at 1.7 similar to 8.7. The limiting thresholds are strongly influenced by the nature of the substituents on the benzene ring, Electron withdrawing groups of the complexes can enhance the limiting capability, while the effect of heavy atom acts opposite roles. The optical limiting abilities are compared with C-60, tetra-phenyl-tetrabenzoporphyrin-zinc and octanoxyl-phthalocyanine free base at same conditions. The sequence of the limiting capability is pentaazadentate cadmium complex >C-60 > tetre-phenyl-tetrabenzoporphyrin-zinc > octanoxyl-phthalocyanine flee base.