Tetrabrominated Lead Naphthalocyanine for Optical Power Limiting

The complex 2,(3)-tetrabromo-3,(2)-tetra[(3,5-di-tert-butyl)phenyloxy]-naphthalocyaninato lead [Br4(tBu2C6H3O)4NcPb, 1] has been prepared and its optical limiting properties for ns light pulses have been measured. Complex 1 behaves as a reverse saturable absorber within the spectral range 440–720 nm with a limiting threshold of 0.1 J cm−2 at 532 nm. The lifetime of the absorbing triplet excited state has been evaluated as 3.8×10−7 s and the quantum yield of triplet formation has been measured as 0.07 in toluene. The nonlinear optical transmission properties of complex 1 have also been determined in Plexiglas [naphthalocyanine content: 5.0×10−4 M (0.1 % by weight)]. A reversible nonlinear absorption was again observed for a fluence above 0.4 J cm−2, but through different excited-state dynamics. This may be rationalized in terms of aggregation of the molecule in the polymer matrix.